Author Topic: Oldest fossils ever discovered raises question of life on Mars  (Read 9197 times)

Offline Ben the Space Brit

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@M.E.T.

Not entirely correct. It has taken 4 billion years to reach us. However, there are few obvious spaceborne artefacts and arguably no macroscopic planetary surface artefacts that would survive even a few million years. So, barring the discovery of an artificial moon or something similar, there is no obvious way to tell if intelligent life arose and subsequently went extinct even as recently as the end of the Neogene epoch.
« Last Edit: 09/27/2017 02:52 PM by Ben the Space Brit »
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Offline DrRobin

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Not often on this forum when a microbiologist like me has something substantive to contribute! First, let's see what the data really are here when the paper is released. It's pretty common for leaked press reports to mangle things. Second, it's alway good to be a bit skeptical when people are pushing up against the limits of what can reasonably be inferred from the data. It sounds like they have found chemical signatures suggestive of biological origin, which is not the same as, say, actual microfossils. That said, there is some value in considering how long things took to appear on Earth relative to the "lifespan" of sun-like stars. Signs of bacterial life can be found in rocks almost all the way back to when the Earth cooled enough to allow liquid water. On the other hand, eukaryotic cells (which have much more complex internal structures) do not appear until more than a billion years after that, and abundant, complex multicellular eukaryotes take more than a billion years after that. Technological intelligence takes "only" a few hundred million years after that (leaving aside the question of what steps come _after_ us). And as the Sun continues to brighten over time, in less than a couple billion years more, the Earth will no longer be able to sustain liquid water, so in the one example we have to work with, Earth will have spent most of its time in the Habitable Zone populated with single-celled life, but technological intelligence was a bit of a close call. Hope is that by studying the chemistry of promising targets over the next few decades (Mars subsurface, Europa, Titan, Enceladus, and perhaps spectroscopic analysis of extrasolar planets), we'll get a better idea of how likely life might be elsewhere.

Offline vjkane

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Not often on this forum when a microbiologist like me has something substantive to contribute! First, let's see what the data really are here when the paper is released. It's pretty common for leaked press reports to mangle things. Second, it's alway good to be a bit skeptical when people are pushing up against the limits of what can reasonably be inferred from the data. It sounds like they have found chemical signatures suggestive of biological origin, which is not the same as, say, actual microfossils. That said, there is some value in considering how long things took to appear on Earth relative to the "lifespan" of sun-like stars. Signs of bacterial life can be found in rocks almost all the way back to when the Earth cooled enough to allow liquid water. On the other hand, eukaryotic cells (which have much more complex internal structures) do not appear until more than a billion years after that, and abundant, complex multicellular eukaryotes take more than a billion years after that. Technological intelligence takes "only" a few hundred million years after that (leaving aside the question of what steps come _after_ us). And as the Sun continues to brighten over time, in less than a couple billion years more, the Earth will no longer be able to sustain liquid water, so in the one example we have to work with, Earth will have spent most of its time in the Habitable Zone populated with single-celled life, but technological intelligence was a bit of a close call. Hope is that by studying the chemistry of promising targets over the next few decades (Mars subsurface, Europa, Titan, Enceladus, and perhaps spectroscopic analysis of extrasolar planets), we'll get a better idea of how likely life might be elsewhere.
While I'm *not* and expert like Dr. Robin in this field, one could argue that after life itself, photosynthesis and the development of complex eukaryotic cells are the key events leading to complex life.  I seem to remember that photosynthesis may have evolved more than once (experts, please correct!) but complex cells evolved just once.  So we might have to modify Drake's equation to include chance that life arises and then for the chances that complex, energy intensive cells arise.  Of course, since we have an N of one, establishing statistical confidence intervals on our estimates is a bit tricky.   :)

Offline as58

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Now that 18:00 GMT has passed, the embargo is over.

Nature News: http://www.nature.com/news/oldest-traces-of-life-on-earth-may-lurk-in-canadian-rocks-1.22685
The original research article: http://dx.doi.org/10.1038/nature24019

edit: a lot of scepticism in that Nature News article...
« Last Edit: 09/27/2017 06:37 PM by as58 »

Offline KelvinZero

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Intelligence emerged very quickly right at the end, with multiple diverse candidates. Octopuses are pretty intelligent. So it sort of seems that intelligence also happens all the time once you get to that point.

There was a long time in the middle where life did nothing of much interest. Eg maybe becoming multicellular was the big hurdle, or the evolution of eukaryotes (something about a cell with its various components inside a membrane)

https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life

There is an interesting statistical phenomenon that when you have a set of fairly unlikely events within a given interval, and you consider only cases where all the events happened to happen, then they tend to distribute themselves fairly evenly, even if one of the events is a billion times less likely than the other.

It is sort of like: If you throw a dart and it hits the center ring of the dart board, then it does not matter if your usual accuracy is to hit somewhere on the board or to throw it over your shoulder. If it hits the center then its probable location will evenly distributed.

So looking at that timeline, it could well be that photosynthesis, eukaryotes and multicellular life are all unlikely to happen on a given planet, but there is no way, from just the timeline, to tell if one of them happens fairly often and one does not occur in multiple universes. We only see the sample where they all happened. That could be enough to divide the timeline into 4 (very roughly) equal-sized sections.
« Last Edit: 09/27/2017 10:12 PM by KelvinZero »

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