a bucketful of problems

while others played spin the bottle, Newton preferred spin the bucket

Canto: I think we should tackle the biggies, space and time, and such, since we've just seen a doco on time and whether it really did begin at the big bang.
Jacinta: We'll only be wading into the shallows, but hey we're here to educate ourselves as best we can, with whatever paltry capacities we have.
Canto: These are not only scientific questions but arguably metaphysical ones. Did space and time begin with the big bang, and if not, then do we go back infinitely somehow, with no first cause? Is the big bang a cause or an effect, or do we have to rethink our language?
Jacinta: The danger here, it seems to me, is to imagine you can come up with the right answer just by thinking about it. That way lies metaphysics, definitely, as well as theology.
Canto: Yes, it's all about basing your thinking on evidence, but in the field of cosmology - or in some areas of cosmology anyway - evidence is very hard to come by. A cosmologist or a string theorist spoke in the doco about his very firm conviction that time didn't begin with the big bang, that it was caused, I think by the clashing of two universe-planes which would in general circumstances remain unconnected, as parallel universes. Now what would constitute evidence for this? How can the theory be tested? As well as all the other theories floating around in cosmology?
Jacinta: It's not exactly metaphysics in the sense of dreamed-up noumenal worlds or the constructions in Plato's Timeaus, it's more mathematically based, and quite likely calculated to extreme degrees of precision, and maybe even testable in terms of some kind of internal consistency, and even coherence with theories already tested and accepted, and yet ...
Canto: So let's stick with the tested theories, and current understandings. What is space?
Jacinta: It's probably something that everyone has a 'common-sense view' about - for example, it's simply what separates discrete objects in the universe. Or it's everything that lies outside of the earth's atmosphere. In  The Fabric of the cosmos, by Brian Greene, the first three chapters - all I've read so far - look at this question, as well as the question of time, as it was wrestled with mainly by three thinkers; Newton, Mach and Einstein. It starts with a bucket experiment described by Newton. A bucket of water is tied by a rope which is twisted around and then let go, so that the bucket spins. The water in the bucket stays still and flat at first, but then, due to friction, the water starts to spin around too, and the surface becomes concave.
Canto: The water's being forced to the edge of the bucket, away from the centre, by the bucket's spinning motion. But how?
Jacinta: The water is being forced around the edge of the bucket, it can't move in a straight line because of the barrier of the bucket's edge. The spinning is the result of containment. The real issue, of course, is motion itself. When the bucket starts to spin, the water doesn't spin. The bucket is spinning relative to the water [and it's key to understand the relativity of all motion]. Then the water starts to spin relative to the bucket - the bucket's relative motion decreases. And the water's surface takes on its concave shape. Interestingly, though, when the bucket's rope untwists and starts twisting the other way, the bucket decelerates, while, for a time, the water continues to accelerate, increasing the relative motion between them once again. The surface of the water remains concave, more concave than ever.
Canto: So you're saying that the relative motion between water and bucket isn't itself responsible for the water's shape. Surely it's about force. The spinning bucket has imparted a force to the water, a force which continues to increase as the bucket accelerates. Even as the bucket slows down, it's still going in the same direction [it's responding to the force of the rope], imparting the same-wise force to the water. Only when the bucket has stopped does it cease to impart any force. The water carries on spinning - and that's where we have to introduce the concept of momentum?

grief, trauma, revenge

Canto: I'd like to bring up a subject not directly related to anything we've been talking about here, but generally related to other life forms, especially the more complex creatures we share the planet with. The intelligence and emotional depth of two such creatures, chimps and elephants, have been brought home to me recently, first [the chimps] by the photo shown above, first sighted by me in The Advertiser back in November, and widely available on the net, and second [the elephants], by a powerful documentary I've just seen on the ABC [The Revengeful Elephant]. Both the image and the documentary highlight the phenomenon of grief, and the acknowledgement of death - features of the lives of other species that our species has, in general, been reluctant to recognize in the past.
Jacinta: Yes, it's a photo to ponder over. We're moving away from the old strictures against anthropomorphizing in ethology it seems, simply because we're coming across so much more evidence of actions and interactions, in the more complex of other species, that we once imagined only ourselves to be capable of. 

Canto: Well let me talk of the elephant documentary, while it's fresh in my mind. In two separate places in Africa, elephants were behaving with unwonted aggression - in national parks in Kenya and in South Africa. In Kenya they were attacking and killing the cattle of the Masai, whereas in South Africa, it was the endangered rhinos. Elephants are herbivores, and these attacks seemed on the surface to lack rhyme or reason. It took years to get to the bottom of it all, but when they did, the findings about elephant behaviour proved revelatory.

Jacinta: I know they’re highly intelligent animals.

Canto: Highly emotional, too, and highly social. This is the key. The ‘bad’ behaviour of the elephants was all about social disruption and trauma. To take the Kenyan situation first, it was found that the elephants doing the killing were females, who had suffered at the hands of the Masai in the past. The Masai had been moved off their land some years before, to make way for the park. Out of resentment, and to highlight their plight, the Masai had attacked and killed a number of baby elephants. In the South African situation, on the other hand, the rhino killers were young bull elephants who had come into musth earlier than usual.

Jacinta: Musth? What’s that?

Canto: Musth is an incompletely understood phase, usually occurring in winter, in which bull elephants secrete a thick substance called temporin from their temporal ducts on each side of the head. During this phase, their testosterone levels can be as much as 60 times higher than normal, and they’re very aggressive, to humans, to other elephants, everyone. The point here is that bull elephants normally only enter the musth phase when they’re quite mature, but these South African bulls were an exception. The final diagnosis was that these ‘teenagers’ were traumatized. In the late seventies, as babies, they’d been transported to the South African park from elsewhere, because in those days only very young elephants could be transported, they didn’t have the technology to ship larger ones. But not only were the baby elephants thus separated from parents and families, in fact their parents were mostly exterminated before their eyes in an elephant cull. They had no role models, and of course they were never treated for post-traumatic stress disorder.

Jacinta: So what did they do then, treat them?

Canto: They brought in older elephants [this was in the early nineties, when transportation technology had improved] who effectively bonded with the younger ones and calmed them down. I don’t know how or if they solved the Kenyan situation.

Jacinta: Revenge killings. That must’ve been a controversial finding.

Canto: Well, possibly not so much of a surprise among these who’ve worked closely with elephants. The old saying that an elephant never forgets must’ve been based on observation. I mean they must have behaved in ways that showed they remembered, and were affected by, events in the past. It makes you feel real empathy with their suffering. You know the two must powerfully affecting moments in the doco for me were these. First, a baby elephant was described as trumpeting in its sleep. It was having a nightmare. Elephants generally only trumpet when there is danger about – it’s a kind of high-adrenalin response. What’s more, baby elephants never trumpet. It’s an adult thing. The second was footage showing an elephant gently and respectfully touching with its trunk the skull of one of its dead fellows. The doco reported extensive evidence of this behaviour as regular and almost ritualized, a behaviour very rare amongst other mammals.

Jacinta: So we seem to be coming to a new anthropomorphism, as we recognize the depth of mourning of chimps and elephants, an anthropomorphism based on a deeper understanding, rather than the old sentimentality.

Canto: Well, I wouldn’t dismiss the old sentimentality too off-handedly. I read Ernest Thompson Seton’s Biography of a Grizzly as a lad, and I was an emotional wreck afterwards. It affected me more than any other book of my childhood, by far, and though it probably was sentimental in parts, it taught me a lot about animals, and especially about respect for them. It would be a good starting point for any budding ethologist. But the new understanding works both ways – it teaches us not only how like us they are, but how like them we are. That we too are mammals, and our social behaviour and morality are no less mammalian than those of many other creatures. It’s exciting and moving and vaguely humbling.

human origins and cladistics

Homo erectus?

Jacinta: When Tudge described Cro-Magnons as 'the first fully modern humans' I think he was referring to their cultural development, or evolution. My guess is that he was referring to fossil remains, in Europe, that were accompanied by other materials – tools, perhaps ornamentations and such artifacts.

Canto: You mean there was no sign that these Cro-Magnons had evolved anatomically or physiologically from the Homo sapiens that they've managed to date back 500,000 years? By the way, can you give some more detail about this dating reference?

Jacinta: Tudge is a little vague on this. Here's the main quote:

The very first people who were more or less like ourselves – who would not have attracted too many stares on today's public transportation – date from about 500,000 years ago.

Canto: Oh so he doesn't specifically call them Homo sapiens. Or does he?

Jacinta: Well that's what I mean, he's a bit cagey. In fact one of the main take-home messages from this book is that we shouldn't get hung up on the 'Homo sapiens' moniker. As you know, there's been something of a shake-up in taxonomy over the past few decades, with clades and grades – what they call cladistics – being the preferred categories, with a lot of slippage and bushiness and imprecision in categorisation. Tudge doesn't give us a lot of detail on the fossils he's talking about from that era – how much material has been found, for example - but he calls them 'archaic', or rather that's what the palaeontologists call them, but though they might be a little different from your modern Cro-Magnon type, they might not be different enough to prevent interbreeding. One definition of a separate species is that it breeds separately, though that definition is disputed, as is everything in taxonomy these days, it seems.

Canto: So we might be talking about the Neanderthals for example.

Jacinta: Yes, and there's another archaic type which has been given a separate species identity, Homo heidelbergensis, but Tudge doesn't provide any further information, whether it's based on half a skeleton or some jaw, or some teeth. Looks like I might have to read another book to get the dirt on that.

Canto: Or do some basic internet research.

Jacinta: We'll get on it soon.

Canto: So tell us a bit more about cladistics, if you can. I know we've talked about this before.

 Jacinta: Well, we're offline at present, because of stupid Optus downloading constraints, so my information will come from two books, The Link, by Colin Tudge, and Galileo's finger, by Peter Atkins. A clade is defined simply by Tudge as a group of creatures that shares a common ancestor. Clades exist within clades which exist within clades, but the key feature of a clade is this, to quote Tudge:

A clade is not a true clade unless it contains all the descendants of any particular ancestor plus the ancestor itself; and it must not contain any other creatures that are not part of the lineage.

This is clearly a tighter definition than what we have for a species, a definition that has changed over time and that has different emphases. For example, Atkins cites biological species, in which breeding pools are the significant factor, but also ecological species, recognition species and phylogenetic species, as well as the earliest understanding of species based on broad similarities. With the tighter approach of cladistics, we can create cladograms [a family tree or bush] which branch off whenever some significantly unique trait emerges. For example the loss of the opposable thumb on the foot occurred sometime after the chimps branched off from us some seven million years ago. That's a missing link, of sorts.

the missing bone

canines have them

Canto: We'll give the global warming crisis a break for a while, and maybe return to the origins of life, or the origins of the universe, or the origins of Homo sapiens – whatever you'd like to focus on.

Jacinta: Thanks for the choice Canto. I'm currently reading The Link, by Colin Tudge, so if we're talking origins, it'll have to be Homo sapiens. It's a great book, it has taught me so much. Frankly, I'm woefully ignorant when it comes to palaeontology, so this has been like an introduction for me, in spite of reading a few Stephen Jay Gould essays.

 Canto: So what specifically have you learned from The Link?

Jacinta: A lot of confusing stuff. That Homo sapiens is maybe 500,000 years old, but that Cro Magnon woman, someone as recognisable as ourselves, is maybe only 40,000 years old.

 Canto: That is confusing. So there's a Homo sapiens that isn't Cro-Magnon? I thought Cro-Magnon and Homo sapiens were interchangeable, that they had found fossils – more than 40,000 years old though – that were just like us, and so they named them Cro-Magnon, presumably after some location...

 Jacinta: We'll try to clarify all that later, but so many other things I've learned, such as that we're the only primate without an os penis – that's a bone in the penis. Every other male primate has one. And most mammals too. And there at least 250 species of living primates, by the way.

Canto: You mean, we human-type blokes have boners without having bones?

Jacinta: Correctamundo.

Canto: And chimps and bonobos, our nearest living relatives, have penis bones?

Jacinta: That's what I've read.

Canto: So when did it drop off, and why?

 Jacinta: Qui sait? The fossil record with regard to our hominid ancestors is extremely patchy –bits of skull, jawbones, teeth. Nothing like the near-perfectly preserved fossil of Ida, the subject of The Link. Not too many penis bones either, not attached anyway. There are speculations as to why humans are penis-boneless though. Here's how Tudge summarises it:

For animals without an os penis, the only way to achieve a convincing erection is by hydrostatic pressure – which only a vigorous animal can generate. An erection achieved without obvious support may not tell a potential mate all she might want to know about her suitor's health, but it does tell her that he is not actually ill, at least in one important respect.

Canto: Yes, the only respect that counts for some women, eh Jass?

Jacinta: Eh?

 Canto: So maybe as we got smarter, we got to convince our females that being sexy was more about thinking sexy, especially when she was around, than about the size of bone in our boner.

Jacinta: Something like that. You could call it the romantic turn.

 Canto: You know, I'm pretty sure that cats don't have an os penis. Have you seen a cat's dick? It's pretty teeny.

Jacinta: I'd have to look more closely at that one.

Canto: Don't excite yourself. Take my word for it. Let's get back to the Cro-Magnon issue, if you please.

a touch of acid

Jacinta: Let's talk today about ocean acidification, or at least let's start off talking about it. Who knows where it will lead.
Canto: There's been a decrease in overall surface ocean pH over the past couple of hundred years, attributed to the uptake of carbon dioxide in the atmosphere, the high levels of which are attributed to human activity. As you might expect, the process of acidification, and its consequences, are complex, but it has much to do with the carbon cycle, particularly the cycle of inorganic carbon. Seawater temperature, along with alkalinity, affects the ratio of carbon dioxide dissolution. This is chemistry stuff - a reaction occurs with the water to form a balance of ionic and non-ionic forms, including 'dissolved free carbon dioxide', carbonic acid, bicarbonate and carbonate. Overall this increases the hydrogen ion content and decreases the pH. It's called acidification, but another way of looking at it is a reduction in alkalinity. The sea is still alkaline.
Jacinta: Yes, the pH of water is 7, that's neutral. They reckon the pH of the surface ocean has come down from a little under 8.2 in the 1700s to a little over 8.1 currently, but that the acidification is accelerating and the  future is looking increasingly grim depending on which expert you consult. And the effects on marine life?
Canto: Shellfish produce calcium carbonate. It's a process called calcification, and it's essential to many marine organisms. I won't go into the chemistry here but unless the surrounding seawater is saturated with carbonate ions, the structures built out of calcification will simply dissolve. It's more complicated than this [for example, it depends on which calcium carbonate structure the organism relies on for calcification - there are two, aragonite and calcite, with varying degrees of solubility], but the saturation state of seawater, which varies with temperature and carbon dioxide levels, is vital to the health of the organisms inhabiting it.
Jacinta: So what organisms are we talking about here?
Canto: A very wide range indeed. Think of corals of course, but also molluscs and crustaceans. And perhaps most importantly, the very abundant single-celled micro-organisms with little calcium carbonate plates, called  coccolithophores. However there's a lot of disagreement, both about the current extent of acidification, and about its long-term, and even short-term impacts. It may not all be doom and gloom, and we should remember the human tendency, generally a positive one, to motivate ourselves into action through these negative projections.
Jacinta: More research is required! More more more!
Canto: That’s right – all scientists want is the opportunity, and the funding, to get to the bottom of all these bottomless issues, to keep on with their research – and who can blame them.

Jacinta: And there are always new crises coming up to concern ourselves with. Have you heard about the methane clathrates under the ocean? They have the potential, apparently, to release such volumes of methane as to send global temperatures skyrocketing, just as might have happened at the time of the Paleocene-Eocene Thermal maximum. Watch this space!

surviving doom and gloom

Jacinta: The 'little ice age' is a complex and controversial event, with the IPCC describing it as a series of more or less connected regional effects rather than a 'globally synchronous increased glaciation'. And since there's just no agreement on the timing and duration of this soi-disant little ice age, it's almost impossible to come to a determination of causes. Possibilities include the usual suspects - low solar radiation, volcanism, natural climate variability, ocean current activity - and some new human factors, which I'm none too convinced about. The fact is, though, that the reasons for the warming between the end of the little ice age, whenever that was, and around 1950, remain unclear. What is quite clear to the vast majority of climatologists is that the warming since 1950 has been largely due to human fossil fuel burning and land clearing.
Canto: From my cursory reading, I gather that Dr Barry Brook is of the view that human effect on greenhouse gas levels and global warming, previous to 1950, and even 1850, has been considerably underestimated. But what I also notice from this cursory reading is how head-spinningly complex this multi-factorial issue actually is. Endless difficulties in measurement, in interpretation, in extrapolation and prediction. It's hardly surprising that nonscientific but naturally sceptical types like myself can be so thoroughly discombobulated, what with radiative forcings, radiosonde data, solar-cycle lengths, carbon sink capacities, tropical hotspots, biomes, urban heat islands, and more and more.
Jacinta: A pleasant puddle of dummy spit there, Canto, but I think it's best if we keep our eye on the big picture, while gradually trying to educate ourselves on these undoubtedly significant details. And the big picture is that there is an apparently accelerating rise in global temperatures, the effects of which are currently being felt especially in the northern hemisphere. The large-scale burning of fossil fuels and the continuing clearing of forest areas that act as carbon sinks, and various other large-scale human practices, seem to be having an effect upon the climate. Certainly this is the consensus view of the experts in the field, and though there may be assessment flaws here and there, and exaggerations on the fringes, we would surely be unwise not to act on this general consensus.
Canto: But what will be the effects of this global warming, and what should we do about it? I mean, given that the Eocene warming led first to extinctions then to speciations, what with the hot and steamy atmosphere just right for reproduction, the future surely doesn't look all bad? Maybe there'll be a collapse of the human population, and after a period the warming will level out, and the cooling trend will start again. That's a reasonable scenario isn't it? And all of this will have a transformative impact on the biosphere, like many previous transformative impacts.
Jacinta: Yes but I think the area of really unfamiliar territory is the speed of this temperature rise. If it continues like this for, say, a century, it might well be more catastrophic than anything that has gone before. I agree though that some species will thrive. Mass extinctions may not have a negative impact on the whole biomass, but it's generally top of the food chain species that are most vulnerable, paradoxically.
Canto: You mean us? I'm not sure if we're talking out of our arses, but it's kind of exciting stuff. I wonder if we somehow require doom and gloom scenarios to get us motivated.

global warming controversies

Canto: Before we go on to look at the causes of modern global warming, how can it be that some aren't convinced that global warming is actually happening? Some are even saying that the globe is cooling.
Jacinta: Well you know that, at least since the Eocene, and probably overall since the beginning of the planet, earth has been cooling, with many fluctuations such as this one. Claims about cooling since 1998 are dealt with here, and on many other sites. The 1998 spike was likely due to a strong El Nino effect, and the 2005 year was also quite warm, but a couple of years of relative coolness since then doesn't buck the overall trend. It's a matter of being patient with data - a year or two's figures aren't enough to reveal an underlying trend.
Canto: And didn't they just release figures for - 2008 was it? Which suggested it was the warmest year on record?
Jacinta: No, 2008 is down at only around equal eighth place, according to the USA's National Oceanic and Atmospheric Administration, and from what I can gather 2009 was warmer, but the decade was the warmest on record - that is, for a mere 150 years or so.
Canto: And even a million years is a mere blip in planetary time.
Jacinta: But we won't get complacent. We want realism, not complacency. This is possibly the fastest upward spike in planetary history, and it may already be out of control.
Canto: So what proof is there that this warming trend is due to human activity?
Jacinta: Here's where we move into difficult waters because of the complexity of the subject. I'm not a scientist, and so I have to defer to the scientists, especially the climatologists of the IPCC who have reached a general consensus on the issue. The February 2007 summary of the IPCC's fourth assessment report stated that there was a ninety percent likelihood that the global warming being experienced was anthropogenic and primarily related to the burning of fossil fuels. This, along with land clearing and other agricultural practices, has increased the level of carbon dioxide and methane in the atmosphere.
Canto: Yet there's a vociferous crowd who argue that this a natural cycle, and that our contribution to the greenhouse gases in the atmosphere is negligible, and even if there is some warming there's no need for all the alarmism. And many of these guys, such as Edward Townes and Joanne Nova and Australia's endless Andrew Bolt, are very tenacious indeed.
Jacinta: And so were the flat-earthers, remember. It's evidence that counts, not tenacity.
Canto: So let's look at the evidence. Joanne Nova presents, on her blog [actually it's guest post by a Dr David Evans], 'a simple proof that global warming is not man-made'. Evans presents graphs and data showing that the vast bulk of emissions occurred after the second world war, with post-war reconstruction and industrialism. In fact, he claims that half of all human emissions [presumably throughout human history] occurred from the seventies on. However, he claims, global warming began after the 'little ice age', approximately from 1700, and has been trending up ever since. He argues that, if it was all to do with anthropogenic emissions, this would be better represented in the figures, with little or no warming before 1945. So what do you say to that?
Jacinta: Next time.

modern global warming

Jacinta: The Eocene epoch lasted from about 56 million years ago to about 34 million years ago, and it obviously can teach us much about climate change, and we will return to it, and maybe try to summarise earth's climatic and atmospheric history, but let's return to the current situation, and the human contribution to global warming.
Canto: Well, first, we need to combat those critics who claim that global warming, anthropogenic or not, isn't even occurring. I mean, there are those who argue that it's much more clear that carbon dioxide levels are increasing than that global warming is happening. Which of course also means that they don't accept the connection between carbon dioxide levels and temperature. So what's the evidence that global warming is occurring, and that it's connected to carbon dioxide levels? Can you explain the nature of that connection?
Jacinta: Okay, we have a number of questions to address here. First, is the planet warming? Second, is the warming due to human activity? Third, what is the nature of the relationship between carbon dioxide levels and global warming? Fourth, what is the nature of the human contribution to global warming? Fifth, how can this contribution be minimized?
Canto: Pretty well summarized. So is the planet warming? After all, as far as I know we only have detailed data about global temperature for, what, about a century and a half, and that is nothing at all in planetary time.
Jacinta: You're talking about direct data, from measuring surface temperature presumably. Of course surface temperature vary considerably and would have to be averaged out, but we can make indirect measurements by checking the volume of greenhouse gases [carbon dioxide, methane, water vapour and CFCs] in the atmosphere. Satellites can measure changes in the infrared radiation spectrum, and in so doing can quantify changing levels of each of the greenhouse gases in turn.
Canto: Yes, so they measure greenhouse gas levels and can compare them with earlier satellite measurements of, say, thirty years ago, but that's not much of a time differential. What about levels 50 thousand years ago, or 50 million years ago?
Jacinta: Let's not complicate matters too much. What they are finding is that these levels are rising quite rapidly in the reasonably short term.
Canto: And what about surface temperatures?
Jacinta: Global surface temperatures rose by around three quarters of a degree celcius over the period of the twentieth century, according to the IPCC.
Canto: That's not much, surely.
Jacinta: The IPCC and most, if not all, climatologists predict that the increase in temperature will accelerate over the twenty-first century, with predictions ranging from one to six degrees celsius. It's not an exact science, the variables are enormous.
Canto: Yes, I heard that the hottest years on record have been the most recent - though that's no indication of an accelerated increase, of course. It's just what you'd expect to find with an increase, even a decelerating increase.
Jacinta: The records show an accelerated increase in fact. This is one of the obvious reasons why the experts predict faster warming in the near future. It has a snowballing effect, with the melting of ice sheets, glaciers, permafrost and so on, and carbon dioxide tends to linger a long time in the atmosphere. So hopefully we've established global warming as a fact.
Canto: Okay, so next we examine the evidence as to causes.

touching on the carbon cycle and the long ago

Canto: Okay, before we go on about this, Jass you said that plants emit carbon dioxide in huge amounts by respiration, and then absorb huge amounts by photosynthesis. This idea of being big emitters and big absorbers at the same time is hard to make sense of. Could you explain that a bit more?
Jacinta: Let me briefly explain the carbon cycle. There are two main sources of carbon in our atmosphere, carbon dioxide and methane. Think of the atmosphere, above us, as at the top of this cycle. At the bottom of the cycle, far below us, the earth's crust and mantle contain carbon which is forced upwards and outwards by volcanic and geothermal activity. The other parts of the cycle are the terrestrial biosphere [our territory - though not owned by us, as we share it with other terrestrial animals and plants], the oceans, and underground sediments [in which are found the fossil fuel reservoirs we're so keen on]. Now the terrestrial biosphere and the oceans in particular can be sinks or sources of carbon dioxide, depending on the balance between absorption and emissions. Because it's a bit like profits and losses, climatologists call this the carbon budget [whether of the oceans, or a particular ocean or region, whatever]. And it's always changing...
Canto: Mmm, and some areas, like rainforests, are really big carbon sinks, right? So if all the land was covered in rainforest, would that mean that the amount of atmospheric carbon would be right down? It would all be somehow fixed in the plants and in the soil?
Jacinta: No, I'm not sure about this, but with lots of rainforest, and that means thick vegetation, lots of plants and lots of animal and insects species thriving on them, you'd have lots of respiration, and lots of rotting, because lots of life also means lots of death and decay. In fact, during the early Eocene epoch there was a burst of warming, probably initiated by releases of methane [a much more potent greenhouse gas] into the atmosphere. I won't go into the reasons for that release here, but there was certainly more carbon dioxide in the atmosphere then than there is now. The Eocene became so warm and wet [the ice caps had melted, inundating much of the land, and water was evaporating from the oceans - water vapour is also a greenhouse gas] that vegetation was springing up everywhere - tropical palms in Alaska and Siberia, for example.
Canto: My god! How did they save the planet?
Jacinta: Well, the planet was going along just fine, which doesn't mean we should be sanguine about the current situation. The Eocene saw an absolute burgeoning of life, as you might imagine, though the short sharp warming burst, which lasted only 100,000 years or so [that's only one two hundredth of the whole epoch] caused a mass of extinctions. And if it wasn't the period of the birth of primates, it was the period of their greatest development and success.
Canto: Wow, this long-term view really puts things in perspective. When exactly was the Eocene epoch?
Jacinta: I'll tell you next time. It's worth reflecting on global climate history and the evolution of species. It's a complex but compelling subject.

a biosphere out of balance?

Canto: There are so many issues around global warming, so many questions to ask. I want to begin with an article I read in a November issue of New Scientist. It was written by Alun Anderson, a former research biologist and editor-in-chief of the magazine. The blurb at the front of the magazine described this piece as 'dispatches from a collapsing ecosystem', but that is very misleading. In fact, Anderson describes a thriving, resurgent ecosystem, that of the Arctic. Polar bears and narwhals and other creatures at the top of the food chain are in trouble there, but killer whales are thriving and taking over at the top. The ecosystem isn't so much collapsing as transforming:

In purely biological terms, the new Arctic will be more productive than the old, because there is more water, open to sunlight for longer, with more plankton growing in it, and more food supports more life. The first signs are already there. After the sudden collapse of the sea ice in 2007, a satellite-borne sensor, measuring the water's 'greenness', showed that the total productivity of the Arctic seas leapt by 40%. That is a big increase. 

These observations underline one particular theme of mine. The 'save the planet' mantra is bullshit. A few degrees of warming is not a threat to our planet. What it does, of course is threaten the biosphere as we know it. It will transform the biosphere, not necessarily for the worse, from a non-human perspective. It will disrupt human activity, though it would be a gross exaggeration, I think, to suggest that it threatens our species' survival.
Jacinta: Yet there are so many unknowns. They say the oceans are becoming more acidic. I don't know if that's directly linked to global warming, but it would presumably be life-threatening to many species. How will this interact with the burgeoning of species, especially in colder regions, due to global warming? But let's get back to the initial question you asked, in the last post. How do we know that greenhouse gas emissions, particularly carbon dioxide, lead to global warming?
Canto: I know that carbon dioxide levels in the atmosphere are continuing to climb, with current levels being at their highest for 650,000 years, but what precisely is the connection between these levels and temperature?
Jacinta: Carbon dioxide levels have remained fairly steady for a long time, with a balance between emissions and absorption helping to maintain relatively stable climatic conditions. As you know, the current level is around 390 ppm, and that's well up on the range in the half million years or more before the twentieth century,  which, according to evidence from ice cores, has been between 180 and 300 ppm. The concern is that emissions are now outstripping absorptions.
Canto: So what, generally, emits carbon dioxide and what absorbs it?
Jacinta: Emissions are measured in gigatonnes. Some 440 Gt of carbon dioxide is emitted annually, about half by plant respiration, and half by consumption of vegetation by microbes and animals. These figures are, incredibly, balanced by the enormous amount of carbon dioxide absorbed annually via photosynthesis. Now, we must look at human emissions...
Canto: Next time.

RNA, complexity, and a change in the weather

RNAP in action during elongation

Jacinta: Right, now I've shown you the chemical structure of one base, adenine. In base pairing in RNA, adenine pairs with uracil, and guanine pairs with cytosine. According to what I've read in Crick, big pairs with small. In DNA, adenine and guanine are relatively big, thymine [and presumably uracil in RNA?] and cytosine are small. Here's a diagram of the chemical structure of uracil:

Canto: Right, only one ring, less components than adenine, certainly. So how and why do these bases pair off?
Jacinta: In DNA the two big and two small base pairs form a neat hydrogen bond. In RNA it's apparently more complicated - there are in fact other base pair bonds - but for our purposes it's the same story. On your comment about rings, yes, the big double-ring molecules, adenine and guanine, are called purines, and the single-ring molecules are called pyrimidines. I could go on, but I'm not sure if mastering all this detail, supposing we can, will get us far in understanding the organic universe.
Canto: Yes, and no. Obviously Darwin didn't know any of this stuff when puzzling over his barnacles and the diversity of species, but that doesn't mean we don't need to know it, or that it's not helpful to know it.
Jacinta: Well I can tell you it gets more complicated, vastly so.
Canto: Okay let's move away from structure and onto function.
Jacinta: In any case let's try to keep it broad. The DNA into RNA thing. An enzyme called RNA polymerase [RNAP], essential to all living organisms, constructs chains of RNA from DNA. Again, this is by no means a simple process, and it is of necessity highly regulated. For example in E coli,more than 100 transcription factors have been found to regulate the activity of RNAP. This enzyme is responsible for many products, including messenger RNA, the non-coding RNA including transfer RNA and ribosomal RNA, and many other recently discovered RNAs. It's an ongoing, burgeoning field of research. Eukaryotic cells have several different types of this enzyme, so it's hard to know where to begin...
Canto: Okay I get the picture, or I get the idea that we're never going to get the picture. Let's just change the subject completely shall we? I'd like to get on something more topical, like our warming planet.
Jacinta: Later, later, Can. Okay, clearly RNA stuff is getting away from us. What's a nucleic acid?
Canto: Something to do with the nuclei of cells, and an acid has a negative charge, a base has a positive charge.
Jacinta: On the right track. The phosphate groups in DNA in normal conditions have a negative charge, that's what makes it an acid, and yes, it's nuclear, except when there's no nucleus. RNA of course is also an acid, very similar to DNA, but without the missing 'oxy' group. The ribose of both these molecules is a sugar.
Canto: Well thanks, I'm definitely learning something here, and we'll get back to it, but i'm wondering if we can explore this more pressing topic next time. Is the rise of carbon dioxide in our atmosphere, presumably due to human activity, the burning of fossil fuel, deforestation and the like, causing the planet's surface to warm, or is the connection between our emissions and warming unproven, as many sceptics are saying?
Jacinta: Okay, we'll get right onto that one, for the sake of our species and many others.

starting from the base

adenine

Canto: You know, just as an aside on this earliest forms of life stuff, it's interesting how the pioneers of modern biology were interested in getting down to the smallest, simplest forms of life, and studying them, to see just how far down they could go, in size, and still find life. I mean they were asking, just how small can a living organism be?
Jacinta: Right, and they were no doubt amazed at the complexity of those little critters, once they developed microscopes powerful enough to detect them and look inside them.
Canto: Well you know Darwin took a microscope with him on the Beagle, a state-of-the-art instrument of the time, and his Beagle notes were more about zoophytes than anything else. Zoophytes were sea creatures - the term is obsolete now - that seemed to have the qualities of plants as well as animals. But he was also intrigued by what he called infusoria, another obsolete term, then given to what we now know are diverse forms of largely water-dwelling eukaryotic micro-organisms. And I'm sure his interest in such organisms ran along these 'how small can life be' lines.
Jacinta: And yet the pioneering microbiologist Christian Ehrenberg considered that there were no 'lower' creatures, and that 'the infusorian has the same sum of organisation-systems as a man'. These were the beginnings of heretical ideas, questioning the role of humanity as the pinnacle of the earth's, or God's, creation. Darwin was definitely being influenced by these new lines of thinking.
Canto: So anyway, we were talking about ribosomal RNA as I recall.
Jacinta: Well you know that the ribosome is the protein-making factory of the cell, right?
Canto: Of course. And so ribosomal RNA is - the RNA in ribosomes, right?
Jacinta: No, it's nowhere near as simple as that, mate. First we know that 'DNA makes RNA makes protein', but it's not a simple process. Certainly rRNA is central to that protein-making process, but there are two other forms of RNA, messenger RNA [mRNA] and transfer RNA [tRNA], that need to be understood and differentiated.
Canto: Yeah, I can see this is going to be horribly complex, but let's just do it. How does DNA make RNA and why does it make these three different types?
Jacinta: Well this first step is called transcription or RNA synthesis. We know that both DNA and RNA are nucleic acids.
Canto: Made up of nucleotides. But what's a nucleotide?
Jacinta: Okay, if you're serious, I'll tell you. A nucleotide has three basic components - a nucleobase, a five-carbon sugar, and a phosphate group [or two, or three]. A nucleobase is involved in base pairing in DNA and RNA. They're often called bases for short. The four bases in DNA are cytosine, guanine, adenine and thymine.In RNA the first three are the same, and uracil replaces thymine.
Canto: Fine, you've named some nucleobases, but what are they?
Jacinta: Well, if you want their chemical structure, you'll find all that here. But aren't we getting a little bogged down?
Canto: No, no, there's no use talking of RNA until we understand the basics, and that includes bases. Let's take it slowly, inch by painstaking inch.
Jacinta: Okay, you're the boss.

Source: Rebecca Stott: Darwin and the Barnacle. Faber & Faber, 2003.

more speculations on earth's early days

Canto: Going back to the origin of life on Earth, one of the most interesting pieces of early speculation came from Charles Darwin, who wrote to his friend Joseph Hooker in 1871:

It is often said that all the conditions for the first production of a living organism are present, which could ever have been present. But if (and Oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc., present, that a protein compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.

Jacinta: Yes, and much later, in the 1950s, the famous Miller-Urey experiment was carried out to try to reproduce life or something like it out of what were then thought to be the conditions of the primordial Earth's atmosphere, including lots of ammonia and methane.
Canto: In fact, the gases they used were those two plus hydrogen and water. Miller then ran a continuous electric current through this mix, to simulate lightning, again believed to be a common feature of the early earth system. After a week, the finding was that more than ten percent of the carbon in the system [provided by the methane] had been transformed into organic compounds, including amino acids, the building blocks of proteins. It seemed almost absurdly easy, then, to create, from these gases, material which was a giant step along the way towards life.
Jacinta: And was this experiment able to be replicated?
Canto: Oh yes and they have pushed further on. One of the interesting things is that, in the years following this experiment, the scientific consensus regarding the earth's early atmosphere moved away from NH3 and CH4 [ammonia and methane] to CO2, CO and N2 from volcanic activity, with UV radiation reducing the ammonia and methane to a short life span. 
Jacinta: But now things have changed again, and it's believed - by some of course - that Stanley Miller and Harold Urey, together with their brilliant predecessor Aleksandr Oparin, might've been right all along. Studies of the outgassing of chondrites [particular types of meteorite fragments representative of early planetary formation] show a preponderance of just the sort of gasses these early experimenters chose to work with.
Canto: So, just how significant was this work, and is it the only pathway to creating life? 
Jacinta: Well, there's the RNA pathway. Apparently, small segments of RNA can form quite easily, though it's less stable than DNA [they're actually very similar molecules], which makes more sense as info-storage molecule essential to life as we know it, but there has been talk for a long time now of a kind of pre-existing RNA world. Though maybe this thesis is already out-dated.
Canto: I don't know about that. Since the early days after Watson and Crick worked out the structure of DNA, when DNA and proteins were all the go, RNA, especially ribosomal RNA, has come to be recognised as surprisingly multifarious in its functions, both potential and actual. 
Jacinta: Good, we'll have to look more closely into all that next time.  

the oldest photosynthesizing organism

Jacinta: It's probable that photosynthesis evolved slowly, bitsily, growing gradually more sophisticated, more complete - by which I mean growing to be what we recognize it as today. For example, modern organisms use photosynthesis to make oxygen, and starches and sugars, from water, but in earlier environments it's likely that something other than water was used.
Canto: Right, if water can be utilized by some sort of redox reaction, then so can other molecules. But how long has water existed on Earth?

Jacinta: Don't sidetrack me Canto. One of the world's foremost authorities on photosynthesis and its origins is Carl Bauer of Indiana University. In the graphic above, taken from the website of Bauer's lab, he presents an outline of the origin of 'oxygen evolving organisms', by which he presumably means photosynthesizing organisms that generate oxygen.
Canto: Right, so he's taking biological carbon fixation back to 3.8 billion years or so.
Jacinta: At that time, our atmosphere was rich in carbon dioxide. In any case, no matter what molecules were used to produce fuel for metabolism, Bauer has found, through detailed phylogenetic analysis, that Rhodobacter, aka purple bacteria are the oldest lineage of photosynthetic organisms on the planet.
Canto: But they don't 'evolve oxygen' as he puts it?
Jacinta: Right, they're anoxygenic. In fact, there are five known branches of microbes that engage in chlorophyll-based photosynthesis, and only one of them, cyanobacteria, evolve oxygen.
Canto: Can you explain what phylogenetic analysis might be - not for me of course, but for our vast readership out there.
Jacinta: Of course. To examine the phylogeny of an organism, or indeed an organ, is to trace its evolutionary development. The phylogenetic analysis we're talking about here involves molecular phylogenetics. Closely related organisms have similar molecular structures, re their genetic material and their proteins. There's a pattern of similarity to related organisms traceable back in time, revealing a pattern of evolution. There's more to it than that, but it'll do for now.
Canto: So tell me more about these anoxygenic purple bacteria.
Jacinta: Well, Rhodobacter have long been of interest to molecular biologists because of their interesting metabolic processes, and they're the most studied of micro-organisms. They live in water - freshwater or marine environments, and their diverse methods of survival - not just through photosynthesis but through a variety of processes - has made them a favourite for study, due to our own concerns about survival.
Canto: Okay, I'll keep them in mind - but you've pointed out that they're aquatic, which raises the question again - when did water first appear on Earth, and what about non-photosynthesizing organisms that might be older than Rhodobacter?
Jacinta: Yes, all that is interesting, along with the actual origins of these Rhodobacter, and the origins of viruses, which we haven't gotten into as yet. Everybody is obsessed with water as an essential source of life, so that when we look for life elsewhere, we tend to look for signs of water - but it ain't necessarily so.
Canto: Wow, lots to explore there - can't wait for our next little chat!

fixation, redox reactions, nucleotides and more

ATP - see the triphosphate bit?

Jacinta: Okay, so since we're both thoroughgoing obsessional types, we'll have to get to the bottom of photosynthesis, at least to clarify some of the cycles and molecules and such that we referred to last time.
Canto: Great, we're talking the same language. So tell me about this fixing, in relation to carbon dioxide. I'm sure I've also heard of nitrogen fixing...
Jacinta: Well let's not get too sidetracked, but fixation, in chemical terms, means transforming a substance, or molecule...
Canto: Or molecular substance?
Jacinta: Yeah, into a more usable form, like ammonia, in the case of atmospheric nitrogen.
Canto: N2 into NH3, I get it.
Jacinta: Right, though of course much more complicated. And carbon fixation is hideously complicated. The Calvin cycle, worked out many decades ago, basically traces the carbon fixation process. All I can competently say at this stage is that the key enzyme in the process has come to be known as rubisco. I won't say anything more about NADPH - it's essential in the photosynthetic process in chloroplasts. I could say more but it wouldn't make much sense to either of us.
Canto: It acts as a reducing agent, doesn't it?
Jacinta: Yes. You know about oxidation-reduction?
Canto: I know of it. If I was a hands-on biochemist or whatever I'm sure I'd know about it.
Jacinta: Actually redox reactions aren't too difficult to understand. They generally involve electron transfer. The reductant, or reducing agent transfers electrons to the oxidant, or oxidizing agent. So the reducing agent gets oxidized, and the oxidizing agent gets reduced.
Canto: Believe it or not, I follow you. So in the Calvin cycle, NADPH is the reduced form of NADP+, and therefore NADP+ is the oxidized form of NADPH.
Jacinta: You read that somewhere mate.
Canto: Yes but it makes sense all the same. So what's ATP? That's a biggie isn't it?
Jacinta: Adenosine triphosphate is indeed a very important wee nucleotide, the key molecule in cellular metabolism.
Canto: Let's do each other's heads in - what's a nucleotide, and what exactly is metabolism?
Jacinta: Come on Canto, metabolism's just what you think it is - it's the breaking down of food to construct proteins, nucleic acids and so forth. Without which not. A nucleotide is a molecule with a particular structure, found in all cells performing various metabolic functions. They also are the bases of polymeric nucleic acids, as well as being the structural units of DNA and RNA.
Canto: Well read Jacinta.
Jacinta: Well digested encore.
Canto: Whatever you say mate. So, getting back to photosynthesis, how did plants, or bacteria, start getting into this?
Jacinta: You could just as well ask how did more complex organisms start using oxygen and other nutrients to sustain themselves, or how did pre-photosynthesizing organisms, or non-photosynthesizing organisms start utilizing whatever they utilized...
Canto: I could just as well, but I asked about photosynthesis.
Jacinta: Okay, it's known that photosynthesis evolved in bacteria and that it's been going on on our planet for at least 2.5 billion years. As to the how, I'll try to answer that in the next post.

more on photosynthesis

a simplified version of glyceraldehide [C3H6O3], a triose three carbon sugar used in photosynthesis

Canto: So is it to be photosynthesis today?
Jacinta: Maybe. Not all life depends on photosynthesis, you realize.
Canto: Uhh, yes of course, but tell me what photosynthesis is, then I can be clear about what it is that life doesn't entirely depend on.
Jacinta: Well, most people know that the oxygen around us, the oxygen we breathe, that we depend upon, has been produced by microbial and planktonic life, in the oceans mainly. Now this oxygen is a kind of waste product of a process that transforms oxides into sugars by means of sunlight. What's really important about photosynthesis, apart from its obvious importance for us, is that it's a process that creates 'food' from the most ordinary, inanimate chemicals around - carbon dioxide and water. Did you know that water was an oxide?
Canto: No. I knew that it contained oxygen, though.
Jacinta: Well there you go. Would you like a glass of dihydrogen monoxide?
Canto: You can't get rid of me that easily. Okay, so your plankton or whatever takes a ray of sunlight, or a photon or whatever, and synthesizes sugars out of carbon dioxide or water. That's as clear as mud.
Jacinta: Well, I seem to remember that the exact mechanisms were worked out only quite recently. Let's take plant photosynthesis. Light energy is absorbed by proteins containing chlorophyll...
Canto: Hang on, hang on - absorbed? What's this absorbed? Is that where a miracle occurs?
Jacinta: A miracle is just something we haven't examined sufficiently.
Canto: Oh how prosaic, how materialist.
Jacinta: Okay I'm not sure if absorption is a technical term but sunlight excites molecules, and I presume that's the key. The excitation results in electron transfer reactions. Chlorophyll is involved, absorbing the light due to its pigmentation, and promoting electrons to higher energy levels, creating free energy.
Canto: The electrons then release energy in returning to their stable or ground state.
Jacinta: Too right. When an electron goes into a higher energy state, the molecule it inhabits is said to have a higher reduction potential, so that it tends to donate electrons. That's how light energy becomes chemical energy, apparently.
Canto: How?
Jacinta: Get an education Canto.
Canto: No I think I understand.
Jacinta: Well what follows is very complex and I can't say I fully understand it myself. Electrons are donated to electron acceptors in an electron transfer chain. There's a whole heap of them, and what results at the end of this chain is a reduced molecule called NADPH. This molecule, along with ATP [which is also produced through this process], is involved in the Calvin cycle which fixes carbon dioxide into triose sugars.
Canto: What? Do you really know what you're talking about Jass? What's this thing called 'fixing' I've heard so much about? What are these molecules? What's a triose sugar?
Jacinta: Okay, you’re right, I’ve not got my head around those details, but there’s so much to explore in this universe, mate. I’ll answer your questions, but I’m also interested in pre-photosynthetic life, and much else besides.

Canto: I can’t wait.

cyanobacteria, meteorites, fossils and photosynthesis

Canto: I'm still wondering about life.
Jacinta: There's a lot to wonder about.
Canto: Well, bearing in mind those rough and ready rules, what is the earliest form of life we know of?
Jacinta: Nobody knows. There are big arguments about the status of viruses, but the earliest candidate we know of, I mean the earliest fossil, was some sort of prokaryote, something like a modern cyanobacterium.
Canto: But it's unlikely that the earliest fossil was the earliest life form. I mean, I know very little about cyanobacteria, and obviously prokaryotes are much less complex than eukaryotes, but even one of those things couldn't have just - spontaneously generated. There must've been precursors.
Jacinta: Surely, but it's worth thinking about timelines here. The earliest prokaryotic fossil - the oldest know fossil of any kind - dates to 3.8 billion years ago. The earth was formed 4.6 billion years ago, and clearly it would've taken some time for it to be ready to sustain life.
Canto: Not so fast about that. We always think of life as we know it,we of little imagination. Look at the archaea so recently discovered. If life can thrive in hot volcanic springs, that certainly extends the range of possibilities.
Jacinta: Good point, but there's another interesting thing about this 3.8 billion date. Have you heard of the Late Heavy Bombardment?
Canto: Come on, forget about Armageddon, this is getting interesting.
Jacinta: No, really, what astronomers call the LHB took place just about 3.8 billion years ago - a heavy shower of meteorites in this region. All our evidence is from the Moon, which as you know is almost as pock-marked as Manuel Noriega's mug. Being a more or less dead rock, the Moon still bears the scars, whereas Earth's surface is shifting and spewing and subducting all over the place, so there's no direct terrestrial evidence of this shower, but it's a reasonable assumption...
Canto: Aha! Life from outer space.
Jacinta: Yes, well, that's one of many hypotheses. It's all very speculative.
Canto: Okay, I won't get carried away. Tell me about this cyanobacteria.
Jacinta: Uhh - do you mean the earliest fossils or cyanobacteria in general?
Canto: Dunno.
Jacinta: Well, cyanobacteria are mainly associated with marine environments, and they're also known as blue green algae. 'Cyano' comes from the Greek for 'blue'.
Canto: Right, as in Cyano de Bergerac, the guy with the big blue nose.
Jacinta: They've been around for a long time, engaging in what's called oxygenating photosynthesis to help transform our planet's atmosphere into something habitable for big beasties like ourselves.
Canto: Wow, photosynthesis, tell me about photosynthesis. But first, you mentioned blue green algae. Now, I would've thought algae were eukaryotic. 
Jacinta: Ah yes, nomenclature and taxonomy, always fraught. The term 'blue green algae' came in long before those distinctions were made and so it has stuck. As to photosynthesis, that's one of those key and fateful processes that link the organic to the inorganic and make our fragile biosphere such an astonishing place.
Canto: You're astonished eyes delight me Jacinta, let's shore up our fragile relationship for a while before you reveal all.
Jacinta: Okay, let me reveal all before we begin. Symbiosis here we come.


Sources:
Frank Ryan, Darwin's blind spot: evolution beyond natural selection. Thomson Texere, 2003


 

life with c & j

Canto: Hi, what's new?

Jacinta: Well I've been wondering about life, in a shallow sort of way.

Canto: What brought that on?

Jacinta: Some reading, of course. What else? Sparks to brighten the imagination.

Canto: To set it aflame.

Jacinta: The analytic imagination.

Canto: Bien entendu. So what about life?

Jacinta: Well, questions lead to more questions. What's the most basic form of life you can think of?

Canto: Hmmm. A virus? A chromosome? Is a chromosome alive? Remember the selfish gene theory? Was it a theory? To be selfish you have to be alive, don't you?

Jacinta: That's a lot of questions. Well done. Generally, I'm not sure that genes are considered to be alive, though they're obviously essential components of life. As we know it.

Canto: Probably depends which microbiologist you're talking to.

Jacinta: They've developed rules about what constitutes a living entity. Or someone has. But rules are made to be broken.

Canto: Let's hear them.

Jacinta: Well, first [but not necessarily first], such an entity has to metabolize. That's to say, it has to absorb something and burn it as fuel to maintain and grow itself. I mean, to provide it with energy. Which rules chromosomes out, maybe?

Canto: I haven't accepted any rules. Anyway, what is a chromosome? Tell me that.

Jacinta: Shit Canto, you gorgeous thing, don't sidetrack me. Let's just spell out these rules first, okay. The second rule is that life has complexity and organisation.

Canto: Right. No living thing that we know of, none that is uncontroversially accepted, prokaryotic or eukaryotic, is simple.

Jacinta: Absolutely. Bacteria are anything but simple. Third rule, but they're not in any order. All living entities reproduce.

Canto: That's almost too obvious. They produce again. Not quite the same as replicate. They don't produce replicas.

Jacinta: Well, near enough.

Canto: Near enough, indeed. Like two circles, neither of them exact.

Jacinta: Exactly. Fourthly, living entities develop. They grow, they absorb, they move, they struggle and suffer.

Canto: Death?

Jacinta: Let's not go there. Fifth, they evolve. That brings us back to those imperfect reproductions of course.

Canto: Like Chinese whispers, they change with changing conditions. They adapt. They want to preserve their identities and they strive for something fresh.

Jacinta: Worth exploring, but not now Canto, not now. Last rule, living entities are autonomous. They're not directed by or entirely dependent on any other living entity.

Canto: Ooh, that's a tricky one. Remind me never to make babies with you Jacinta. You'd see it as a living entity and therefore autonomous, and I'd be stuck with all the feeding, arsewiping, example-setting, obstacle-reducing, etc etc.

Jacinta: As if. But you're right, this is the most troublesome rule, and maybe the weakest. Where would a bacterium be without a colony - or an ant, for that matter?

Canto: A rough and ready set of rules.

Jacinta: Makeshift.

Canto: A starting point. So what is life?

Jacinta: I'm not sure, but here's to it loverboy.


Sources:
Peter Ward, Life as we do not know it: the NASA search for [and synthesis of] alien life. Viking, 2005