Posted by
michael
on from the kidnapped-mulder's-sister dept.
BenGarvey writes "CNN.com cites a new study claiming huge meteors hit the Earth and Moon around the time that life formed, leaving two possible conclusions. That any existing life died out and had to start again, or the "panspermia" theory of life arriving on the meteors themselves."
Time scale for life to get started?
by
bcrowell
·
· Score: 2
The finding is an interesting part of the history of life on our planet, but I don't think it's valid to use it as an argument for panspermia. The panspermia argument says there wasn't enough time for life to get started from scratch between when the impacts happened and when the first evidence for life occurs.
But how much time is enough? We really know very little abou the biochemical processes that led to the first life. For example, there may have been an RNA-only world before the current RNA/DNA setup, but the original genetic code may have been even simpler than RNA or DNA. We just don't know. Given that we know essentially diddly squat about the very beginnings of life, how do we know what the time-scale would be for it to happen?
I was also left wondering if there's any proposed mechanism for creating such a plague of impacts. I would have imagined the impacts to be pretty much uncorrelated in time.
As already descibed in Robert Zubrin's "Entering Space". It is possible for many Earth bacteria to survive short trips in space. Therefore, even if all life was completely wiped out on Earth itself, it's perfectly possible that Earth bacteria survived a relatively short trip with some debris in space and then recolonized the planet.
Or the bacteria simply spored while the atmosphere was choked, and survived on Earth.
Or the first organisms on Earth weren't dependent on the Sun. Chemosynthesis of geothermally-synthesized chemicals is a perfectly reasonable basis for a biosphere, and some theorize that the majority of Earth organisms are actually part of an underground chemosynthetic ecology. (They even argue that petroleum may not be a fossil fuel, but a byproduct of this ecology, which explains several facts the fossil theory does not.)
Other theories may also be viable, of course, but I happen not to know what they may be...
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But how much time is enough? We really know very little abou the biochemical processes that led to the first life. For example, there may have been an RNA-only world before the current RNA/DNA setup, but the original genetic code may have been even simpler than RNA or DNA. We just don't know. Given that we know essentially diddly squat about the very beginnings of life, how do we know what the time-scale would be for it to happen?
I was also left wondering if there's any proposed mechanism for creating such a plague of impacts. I would have imagined the impacts to be pretty much uncorrelated in time.
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As already descibed in Robert Zubrin's "Entering Space". It is possible for many Earth bacteria to survive short trips in space. Therefore, even if all life was completely wiped out on Earth itself, it's perfectly possible that Earth bacteria survived a relatively short trip with some debris in space and then recolonized the planet.
Or the bacteria simply spored while the atmosphere was choked, and survived on Earth.
Or the first organisms on Earth weren't dependent on the Sun. Chemosynthesis of geothermally-synthesized chemicals is a perfectly reasonable basis for a biosphere, and some theorize that the majority of Earth organisms are actually part of an underground chemosynthetic ecology. (They even argue that petroleum may not be a fossil fuel, but a byproduct of this ecology, which explains several facts the fossil theory does not.)
Other theories may also be viable, of course, but I happen not to know what they may be...
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