Giant Meteor Hit Earth as Life Formed

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."

dammit

[Kenshin]

well, I imagine that kinda thing evokes the same kind of "OH FUCK!" type reaction as when someone drops a cake on the floor right after it's been taken out of the oven...

Re:Or microbes survived.

[thogard]

Chlorophyll and mitochondria are an essential part of every typical cell but these things look like they used to live indpendant of their now required host cells. Odd thing is the O2 is quite toxic to both of them. They also have a very low rate of mutations.

How does pangaea fit in?

[thogard]

Pangaea had to be a result of something late in the planet formation stage of the earth or else the planet would have been more uniform. I wonder if some form of life was here before whatever event cuased pangaea (and the moon?)

Re:Or microbes survived.

[elakazal]

Actually, I'd have to say that chemosynthesis is a more likely mechanism for early organisms than photosynthesis, since most accounts of early earth I've heard include constant cloud cover and lots of nasty chemicals that need to be broken down by something before we can get to the point we're at now.

Given the high reproductive rate and thus high mutation rate, bacteria seem very unlikely to have been entirely wiped out by anything short of crashing into the sun.

Re:Time scale for life to get started?

[elakazal]

I have a difficult time imagining a functional genetic system more simple than nucleic acids. Correct me if I'm wrong here...I've got a great deal of experience in genetics, but I must admit that I suck on the strict chemistry end of it.

RNA-only seems perfectly plausible to me, though.

While it may not be especially compelling evidence FOR panspermia, it certainly isn't an argument against it. Whether or not there might have been enough time for life to evolve (which is impossible to know for sure), the fact is that to my mind it's no more or less unreasonable to think the life came here from somewhere else than that it sprung out of nowhere here.

Re:How does pangaea fit in?

[narratorDan]

If the Earth was formed out of a molten ball of space rubble, then the surface should have been more uniform and less likely to have a single Pangaea aka super continent. However Pangaea could have been formed by the shock wave of this asteroid traveling through the core of the Earth and pushing up a large area of the crust on the other side. This asteroid could also have formed the fault lines that eventually split up Pangaea with the help of technonic forces from the later development of the Moon. This asteroid could also have displaced enough material to form the Moon.
Before this even the sea levels on the Earth may have been too deep for the development of signifigant (sp?) self replicating chemicals. On the other hand there may have been a number of sites for the successful development of these chemicals around the edges of minor meteorite impacts.

Re:Time scale for life to get started?

[bcrowell]

The RNA-world hypothesis is a pretty standard one. I'm not an expert on genetics or chemistry :-), but IMHO modern genomes might have a lot of fancy features that are necessary to survive today, but might have been unnecessary in a less competitive early-life environment:

• separation of phenotype from genotype
• error-checking
• a well-defined genome "address space" rather than just a bag of genes that all do their own thing

Now, if you showed a biologist a system that, e.g., didn't have a separate phenotype and genotype, they probably wouldn't even consider it alive. But when evolving from nonlife to life, there obviously has to be a whole gray area in between.

While it may not be especially compelling evidence FOR panspermia, it certainly isn't an argument against it.
I see no real reason to introduce an extra hypothesis like panspermia when there's no evidence for it. Panspermia is testable, however. We should send an uncrewed sample-return mission to Mars sooner rather than later. If, for example, it brings back Martian bacteria that use DNA and RNA, that would be extremely strong evidence for panspermia!

re which way

[bcrowell]

Mars' surface solidified earlier than Earth's because of its larger surface-to-volume ratio. It probably had the right conditions for life to get started before Earth did.

Genetic techniques have also allowed a tree of life to be constructed for earth life, showing that the archaea (bacteria found today in extreme environments) are the most similar to the common ancestor. Presumably one could extend that technique and see whether the earliest branch on the tree of life was Mars or Earth life.

Anyhow, if we found life on Mars, it would be one of the two or three greatest scientific events ever, even if the genetic evidence showed that panspermia was wrong!

Time scale for life to get started?

[bcrowell]

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.

Or microbes survived.

[Throw Away Account]

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...