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Why is there only one "beginning of life" on earth? If life is likely to form in earth-like conditions after a few billion years, shouldn't there be more than o

by xpda 11y ago

Why is there only one "beginning of life" on earth? If life is likely to form in earth-like conditions after a few billion years, shouldn't there be more than one "last universal ancestor"? Does this suggest that life on other earth-like planets may be very rare, or that ours is a unique life form for our environment?

codezero 11y ago
This doesn't imply there is one beginning, I think (with no attempt at proof) it's possible there were multiple, but it's pretty easy for things to get wiped out and to lose part of the chain. The last universal ancestor is just the one that you can get to by not breaking the chain. As to your questions, they have vexed scientists and philosophers for ages, so there're no easy answers, but I am assuming you didn't expect one! The conditions for life as we know it are bounded, so that reduces the surface area of possible places life could exist. Add to that, the requirement that the bounds not change dramatically for long periods of time, and they reduce further. The universe is pretty huge, though, so there's a lot of opportunity for life out there, but because it's so huge, and because life is so fleeting, there's a lot less opportunity for two unique forms of life from different planets, solar systems, or galaxies to actually cross paths at the same time, or even to do so before one dies off. For further reading, check out the Drake Equation [1] and Fermi's Paradox [2]. [1] http://en.wikipedia.org/wiki/Drake_equation http://en.wikipedia.org/wiki/Drake_equation [2] http://en.wikipedia.org/wiki/Fermi_paradox http://en.wikipedia.org/wiki/Fermi_paradox
contravariant 11y ago
They're not saying that there's only one universal ancestor only that of all the universal ancestors, one must have been the most recent. Which is almost certainly true, if in fact there exists a universal ancestor. Perhaps you meant to ask if there could have been no universal ancestor? In that case I think most evidence points the other way. There could possibly have been multiple 'origins' of life but those seem to have died out or have been driven to extinction by our ancestors.
kmicklas 11y ago
It's very possible that life arose independently multiple times, but one group grew fast enough to drive all the others to extinction. The life forms we observe now almost certainly came from one ancestor due to the numerous molecular similarities (e.g. use of the same form of DNA).
- NickNameNick 11y ago
  That ignores the possibility that early forms of life combined to form fitter symbiotic life forms. The parallel that comes to mind is the mitochondria within animal cells, they probably originated as independent bacteria.
ufo 11y ago
There are many reasons for why life would only have appeared once on earth. Firstly, the current environment is radically different from the conditions in early earth: * Atmosphere composition has changed a lot, and largely due to the presence of life (more oxygen, no more ammonia, etc). * In early earth it would be possible for complex organic compounds to accumulate in the environment. Nowadays, those would be rapidly consumed by life forms. There is also a matter of competition: * Almost every ecological niche on earth is already occupied by life and there is very little space left for alternate life forms to evolve into. * Current life forms compete against each other and that competition might also affect other nascent life forms. For example, one of the leading theory on the origin of life predicts that early life was largely RNA-based but nowadays lots of the planet is coated in RNA-digesting enzymes that organisms excrete as a form of protection against viruses. In fact, scientists working with RNA have to be very careful to avoid having their RNA be degraded by environmental enzymes.
bediger4000 11y ago
People have seriously suggested that the Eukaryotes and Archea have a different DNA than the Prokaryotes: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC148579/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC148579/ That is, DNA evolved twice on Earth. That seems like "life beginning more than once" or something very close. Note that almost everyone involved thinks that mitochondria and chloroplasts are prokaryotes captured one way or another by Eukaryotes, so the distinction about two evolutions of DNA gets a bit messy.

by xpda 11y ago

codezero 11y ago

This doesn't imply there is one beginning, I think (with no attempt at proof) it's possible there were multiple, but it's pretty easy for things to get wiped out and to lose part of the chain. The last universal ancestor is just the one that you can get to by not breaking the chain. As to your questions, they have vexed scientists and philosophers for ages, so there're no easy answers, but I am assuming you didn't expect one! The conditions for life as we know it are bounded, so that reduces the surface area of possible places life could exist. Add to that, the requirement that the bounds not change dramatically for long periods of time, and they reduce further. The universe is pretty huge, though, so there's a lot of opportunity for life out there, but because it's so huge, and because life is so fleeting, there's a lot less opportunity for two unique forms of life from different planets, solar systems, or galaxies to actually cross paths at the same time, or even to do so before one dies off. For further reading, check out the Drake Equation [1] and Fermi's Paradox [2]. [1] http://en.wikipedia.org/wiki/Drake_equation http://en.wikipedia.org/wiki/Drake_equation [2] http://en.wikipedia.org/wiki/Fermi_paradox http://en.wikipedia.org/wiki/Fermi_paradox

contravariant 11y ago

They're not saying that there's only one universal ancestor only that of all the universal ancestors, one must have been the most recent. Which is almost certainly true, if in fact there exists a universal ancestor. Perhaps you meant to ask if there could have been no universal ancestor? In that case I think most evidence points the other way. There could possibly have been multiple 'origins' of life but those seem to have died out or have been driven to extinction by our ancestors.

kmicklas 11y ago

It's very possible that life arose independently multiple times, but one group grew fast enough to drive all the others to extinction. The life forms we observe now almost certainly came from one ancestor due to the numerous molecular similarities (e.g. use of the same form of DNA).

NickNameNick 11y ago
That ignores the possibility that early forms of life combined to form fitter symbiotic life forms. The parallel that comes to mind is the mitochondria within animal cells, they probably originated as independent bacteria.

ufo 11y ago

There are many reasons for why life would only have appeared once on earth. Firstly, the current environment is radically different from the conditions in early earth: * Atmosphere composition has changed a lot, and largely due to the presence of life (more oxygen, no more ammonia, etc). * In early earth it would be possible for complex organic compounds to accumulate in the environment. Nowadays, those would be rapidly consumed by life forms. There is also a matter of competition: * Almost every ecological niche on earth is already occupied by life and there is very little space left for alternate life forms to evolve into. * Current life forms compete against each other and that competition might also affect other nascent life forms. For example, one of the leading theory on the origin of life predicts that early life was largely RNA-based but nowadays lots of the planet is coated in RNA-digesting enzymes that organisms excrete as a form of protection against viruses. In fact, scientists working with RNA have to be very careful to avoid having their RNA be degraded by environmental enzymes.

bediger4000 11y ago

People have seriously suggested that the Eukaryotes and Archea have a different DNA than the Prokaryotes: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC148579/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC148579/ That is, DNA evolved twice on Earth. That seems like "life beginning more than once" or something very close. Note that almost everyone involved thinks that mitochondria and chloroplasts are prokaryotes captured one way or another by Eukaryotes, so the distinction about two evolutions of DNA gets a bit messy.