The origin of life on earth being coincident with the end of the late heavy bombardment could entirely be an artifact of the fact that no rock from before that time survives to this day. It could well be older on Earth. The reworking of the crust was not complete at any given time, it took hundreds of megayears and at any given time most of the crust would be undisturbed.
Water in the inner system has the complication of the fact that not only do you need to get water, you need to hold onto water. Small objects will not hold onto light molecules out of sheer gravity issues. Mars is not holding onto water or other atmospheric gases well at all because of both gravitational issues, and solar radiation sputtering the upper atmosphere off into space. Venus has all the gravity it could need, but A—no geomagnetic field (at least at this point in its history) and B—got so hot that all the water went into the atmosphere, where it gets cracked by radiation in the upper atmosphere and the hydrogen leaves (allowing the oxygen to react with volcanic gases giving you sulfuric acid and phosphoric acid and the like). The same process happens on Earth but the pool of atmospheric water is SO MUCH SMALLER due to all the liquid volume and the fact that we have this lovely temperature trap in our atmosphere that makes it condense out before it gets too high up that the rate is extremely small.
I would say the only time you can call humans ‘dominant’ is after the widespread adoption of agriculture, which was much more gradual than many people think—people were probably propagating seedless figs 20k years ago and much longer ago were altering the composition of plants and animals in various biomes just via their actions. Since agriculture got big we have become ecosystem engineers in the vein of bears, but rather larger in our effects. We have been creating new large-scale-symbiotic biomes where plants and animals flow matter and energy into each other and where we take care of dispersal rather than the plants themselves doing as much of it, for example. That’s the unique aspect of humanity. Since then we have also started breaking into non-biological forms of energy—raw sunlight, water flow, the black rocks that are basically 500 megayears of stored sunlight—and have been using those for our purposes too in addition to the biological energy flow that all other biomes deal with.
It will be very interesting to see how human ecology continues to change after the extremely concentrated energy sources that represent most of the power we have used over the last 200 years go away. The end result might be very big but might not have the sheer flux of inefficient extractive growth—think weeds colonizing a freshly plowed field, versus an old-growth forest.
That is a very interesting question and one which there’s constant research going into.
A few initial points. First, its becoming clearer and clearer that ‘prokaryotes’ is a very poor grouping to use for much of anything. The bacteria most of us think of are the smaller, faster-replicating members of the eubacteria. There’s also the archaebacteria, which are deeply and fundamentally different from the eubacteria in their membrane composition, cell wall structure, DNA organization, and transcription machinery.
Second, it’s becoming more and more clear that the eukaryotes are indeed the result of an early union of eubacteria and archaebacteria. I saw some very cool research at a conference last December bolstering the “eocyte hypothesis”—the idea that the Eukaryotic nuclear genome roots in one particular spot of the archaebacterial tree plus loads of horizontal gene transfer from the eubacteria that became the mitochondria. You can’t root it there just by aligning things, this was long enough ago that base sequence is effectively randomized, you need to look at what sorts of proteins exist, characters that change very rarely as opposed to mere sequence, and its a very hard question that has required a LOT of sequence data from a LOT of organisms. Most of our DNA structure and transcription and some of our protein processing looks like the archaebacteria, but basically all of our metabolism looks like the eubacteria. This is interesting in the light of recent discoveries of symbiotic pairings of archaebacteria and eubacteria in nature in which they exchange metabolic products.
Anyways, the eubacteria and archaebacteria have deeply different transcription machinery and make their membranes in fundamentally different ways. Central carbon metabolism is all but identical though as is a lot of other pathways, and the core biochemistry. I’ve seen work proposing that the eubacteria and archaebacteria may have diverged before living things managed to synthesize their own membrane components rather than scavenging them from the environment. I’ve also seen interesting work to the effect that certain clay minerals can assemble fatty acids and other such membrane-building substances from acetate under the proper energetic conditions.
There’s also a lot of diverstiy in DNA and RNA processing methods that isn’t in any of the cellular life – there are truly bizarre ways of doing this that you only find in viruses. Viruses mutate incredibly rapidly and so you cannot try to root them anywhere, they change too fast. That being said there are proposals that they may be primordial, elements of the very wide range of possible nucleic acid processing mechanisms that existed before the current forms of cellular life really were established and took off. The eubacterial and archaebacterial models may have taken off with remnants of the rest winding up parasitizing them.
Rampant horizontal transfer of genes, especially early when cell identity might not have been so strong, makes all this very complicated.
There’s a school of thought in origin of life research that autocatalytic metabolism was important, and another that replicating polymers were important. The former posits that metal-ion driven cyclical reactions like the citric acid cycle can take off and take over, and wind up producing lots of interesting chemical byproducts that can then capture it and become discrete self-replicating units. The latter points out that elongating polymers in membrane bubbles speed the growth and splitting of these bubbles. They’re both probably important. It should be noted too that these ideas intersect – one of the popular metabolic ideas, polyphosphate, is actually represented in our nucleic acids. Polyphosphate is an interesting substance that can be built up by the right chemial reactions, and can drive other ones when it breaks down. Every ATP, GTP, etc is a nice chemical handle on the end of a chain of three phosphates – a short polyphosphate. By breaking down those polyphosphates you build polymers.
Proteins obviously came very early and gave a huge advantage, and the genetic code is damn near universal with all deviations from the standard one obvioulsy coming in after the fact. Whatever could make proteins probably took over quickly. The initial frenzy, whatever it was, probably eventually lead to a diverse population of compartments processing their nucleic acids in diverse ways and sending pieces of their codes back and forth, which eventually gained advantages by building their own membranes, and eventually cell walls, in different ways. Some of these populations probably took off like mad, making the eubacteria and archaebacteria, and others remained only as horizontally transferred elements like viruses or transposons or the like.
Written in a hurry, may be edited or clarified/extended later.
A clade of archaebacteria found via metagenomics at an undersea vent (uncultured). Contains huge numbers of eukaryotic characteristic genes that are important for formerly eukaryotic specific functions. The eukaryotes cluster within this clade rather than as a sister clade.
The origin of life on earth being coincident with the end of the late heavy bombardment could entirely be an artifact of the fact that no rock from before that time survives to this day. It could well be older on Earth. The reworking of the crust was not complete at any given time, it took hundreds of megayears and at any given time most of the crust would be undisturbed.
Water in the inner system has the complication of the fact that not only do you need to get water, you need to hold onto water. Small objects will not hold onto light molecules out of sheer gravity issues. Mars is not holding onto water or other atmospheric gases well at all because of both gravitational issues, and solar radiation sputtering the upper atmosphere off into space. Venus has all the gravity it could need, but A—no geomagnetic field (at least at this point in its history) and B—got so hot that all the water went into the atmosphere, where it gets cracked by radiation in the upper atmosphere and the hydrogen leaves (allowing the oxygen to react with volcanic gases giving you sulfuric acid and phosphoric acid and the like). The same process happens on Earth but the pool of atmospheric water is SO MUCH SMALLER due to all the liquid volume and the fact that we have this lovely temperature trap in our atmosphere that makes it condense out before it gets too high up that the rate is extremely small.
I would say the only time you can call humans ‘dominant’ is after the widespread adoption of agriculture, which was much more gradual than many people think—people were probably propagating seedless figs 20k years ago and much longer ago were altering the composition of plants and animals in various biomes just via their actions. Since agriculture got big we have become ecosystem engineers in the vein of bears, but rather larger in our effects. We have been creating new large-scale-symbiotic biomes where plants and animals flow matter and energy into each other and where we take care of dispersal rather than the plants themselves doing as much of it, for example. That’s the unique aspect of humanity. Since then we have also started breaking into non-biological forms of energy—raw sunlight, water flow, the black rocks that are basically 500 megayears of stored sunlight—and have been using those for our purposes too in addition to the biological energy flow that all other biomes deal with.
It will be very interesting to see how human ecology continues to change after the extremely concentrated energy sources that represent most of the power we have used over the last 200 years go away. The end result might be very big but might not have the sheer flux of inefficient extractive growth—think weeds colonizing a freshly plowed field, versus an old-growth forest.
Dear CellBioGuy, what is your intuition on what preceded procaryotes?
That is a very interesting question and one which there’s constant research going into.
A few initial points. First, its becoming clearer and clearer that ‘prokaryotes’ is a very poor grouping to use for much of anything. The bacteria most of us think of are the smaller, faster-replicating members of the eubacteria. There’s also the archaebacteria, which are deeply and fundamentally different from the eubacteria in their membrane composition, cell wall structure, DNA organization, and transcription machinery.
Second, it’s becoming more and more clear that the eukaryotes are indeed the result of an early union of eubacteria and archaebacteria. I saw some very cool research at a conference last December bolstering the “eocyte hypothesis”—the idea that the Eukaryotic nuclear genome roots in one particular spot of the archaebacterial tree plus loads of horizontal gene transfer from the eubacteria that became the mitochondria. You can’t root it there just by aligning things, this was long enough ago that base sequence is effectively randomized, you need to look at what sorts of proteins exist, characters that change very rarely as opposed to mere sequence, and its a very hard question that has required a LOT of sequence data from a LOT of organisms. Most of our DNA structure and transcription and some of our protein processing looks like the archaebacteria, but basically all of our metabolism looks like the eubacteria. This is interesting in the light of recent discoveries of symbiotic pairings of archaebacteria and eubacteria in nature in which they exchange metabolic products.
Anyways, the eubacteria and archaebacteria have deeply different transcription machinery and make their membranes in fundamentally different ways. Central carbon metabolism is all but identical though as is a lot of other pathways, and the core biochemistry. I’ve seen work proposing that the eubacteria and archaebacteria may have diverged before living things managed to synthesize their own membrane components rather than scavenging them from the environment. I’ve also seen interesting work to the effect that certain clay minerals can assemble fatty acids and other such membrane-building substances from acetate under the proper energetic conditions.
There’s also a lot of diverstiy in DNA and RNA processing methods that isn’t in any of the cellular life – there are truly bizarre ways of doing this that you only find in viruses. Viruses mutate incredibly rapidly and so you cannot try to root them anywhere, they change too fast. That being said there are proposals that they may be primordial, elements of the very wide range of possible nucleic acid processing mechanisms that existed before the current forms of cellular life really were established and took off. The eubacterial and archaebacterial models may have taken off with remnants of the rest winding up parasitizing them.
Rampant horizontal transfer of genes, especially early when cell identity might not have been so strong, makes all this very complicated.
There’s a school of thought in origin of life research that autocatalytic metabolism was important, and another that replicating polymers were important. The former posits that metal-ion driven cyclical reactions like the citric acid cycle can take off and take over, and wind up producing lots of interesting chemical byproducts that can then capture it and become discrete self-replicating units. The latter points out that elongating polymers in membrane bubbles speed the growth and splitting of these bubbles. They’re both probably important. It should be noted too that these ideas intersect – one of the popular metabolic ideas, polyphosphate, is actually represented in our nucleic acids. Polyphosphate is an interesting substance that can be built up by the right chemial reactions, and can drive other ones when it breaks down. Every ATP, GTP, etc is a nice chemical handle on the end of a chain of three phosphates – a short polyphosphate. By breaking down those polyphosphates you build polymers.
Proteins obviously came very early and gave a huge advantage, and the genetic code is damn near universal with all deviations from the standard one obvioulsy coming in after the fact. Whatever could make proteins probably took over quickly. The initial frenzy, whatever it was, probably eventually lead to a diverse population of compartments processing their nucleic acids in diverse ways and sending pieces of their codes back and forth, which eventually gained advantages by building their own membranes, and eventually cell walls, in different ways. Some of these populations probably took off like mad, making the eubacteria and archaebacteria, and others remained only as horizontally transferred elements like viruses or transposons or the like.
Written in a hurry, may be edited or clarified/extended later.
Of interest!
Even more recent evidence for the eocyte hypothesis!
http://www.the-scientist.com/?articles.view/articleNo/42902/title/Prokaryotic-Microbes-with-Eukaryote-like-Genes-Found/
A clade of archaebacteria found via metagenomics at an undersea vent (uncultured). Contains huge numbers of eukaryotic characteristic genes that are important for formerly eukaryotic specific functions. The eukaryotes cluster within this clade rather than as a sister clade.