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Life on Earth maybe 4.1 billion years old?

PB666

By PB666
in Science & Spaceflight

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KerikBalm

KerikBalm

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Posted (edited)

http://www.reuters.com/article/2009/05/20/us-asteroids-idUSTRE54J5PX20090520

Its not the uncertainty in the dating, its uncertainty in the evidence.

C12/C13 ratios aren't exactly incontrovertible proof.

https://www.newscientist.com/article/dn14245-did-newborn-earth-harbour-life

"But it is too early to say for certain whether the carbon might indicate life. “We can’t say now that we have unambiguous evidence of life before the Late Heavy Bombardment,†Geisler told New Scientist.

That’s because certain non-biological chemical reactions can also create light carbon, although the ratio is so skewed towards the lighter isotope that these reactions can’t easily account for it.

A reservoir of light carbon might also indicate that simple organic compounds might have existed on Earth, priming the environment for the later emergence of life"

Anyway, Earth had oceans long before the LHB, supposedly... and the LHB wouldn't have completely sterilized the Earth... so... why not?

The problem is we don't have many rocks from before the LHB, so there's not much to go on.

Who knows how long life took to evolve. I have no problems with the idea that maybe it was around before the LHB, and thats why traces of it show up so suddenly after the LHB.

Edited by KerikBalm
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PB666

PB666

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http://www.reuters.com/article/2009/05/20/us-asteroids-idUSTRE54J5PX20090520

Its not the uncertainty in the dating, its uncertainty in the evidence.

C12/C13 ratios aren't exactly incontrovertible proof.

https://www.newscientist.com/article/dn14245-did-newborn-earth-harbour-life

"But it is too early to say for certain whether the carbon might indicate life. “We can’t say now that we have unambiguous evidence of life before the Late Heavy Bombardment,†Geisler told New Scientist.

That’s because certain non-biological chemical reactions can also create light carbon, although the ratio is so skewed towards the lighter isotope that these reactions can’t easily account for it.

A reservoir of light carbon might also indicate that simple organic compounds might have existed on Earth, priming the environment for the later emergence of life"

Anyway, Earth had oceans long before the LHB, supposedly... and the LHB wouldn't have completely sterilized the Earth... so... why not?

The problem is we don't have many rocks from before the LHB, so there's not much to go on.

Who knows how long life took to evolve. I have no problems with the idea that maybe it was around before the LHB, and thats why traces of it show up so suddenly after the LHB.

You are placing way too much stock in the current values, if you only knew how much of those estimates were based on movable assumptions, you wouldn't.

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magnemoe

magnemoe

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Heres a better link: http://www.sciencedaily.com/releases/2015/10/151019154153.htm

Anyways, if life got a start that soon (the latest estimate before this one was 3.9 I believe), then that is a pretty dang good sign if life gets started within a few hundred million years of Earths formation.

How fast life started on earth give some indications in how easy it is to start.

Yes its just statistic but the best it get, say life start 100 million years after possible, if mean time is once every 100 million years we are average, yes life can be rarer and we lucky but that is an lower probability chance. just as plausible that life is even easier and we are slow.

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KerikBalm

KerikBalm

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You are placing way too much stock in the current values, if you only knew how much of those estimates were based on movable assumptions, you wouldn't.

I am aware of the problems in the assumptions.

But the bigger problem is the assumptions in the evidence.

You can have the most precise dating that you want for a piece of evidence that is completely ambiguous...

We already have the case where above ground nuclear testing requires recalibration of dating methods for more recent events.

1.7 billion years ago, there were natural nuclear reactors on earth because U-235 (half life ~700 million years) was more abundant.

4 billion years ago, U-235 would be even more abundant... but we've got very little evidence from that time, and we don't now if there were earlier reactors, or how they might affect things.

But the Uranium-Zircon zircon dating method is actually very good, other methods for younger samples have problems that it doesn't.

However... the C12 to C13 ratio itself is the problem here... *that* has a lot of assumptions before you can call it evidence of life.

Compared to the Uranium-Lead dating assumptions, the C12 to C13 ratio is the problematic thing here.

But to the bigger question... Earth had oceans before the LHB... a log time before the LHB. Life seems to show up shortly after the LHB (although how short is a matter of debate... 3.5 billion years are the oldest fossil microbial mats, but 3.7 billion has a "good" C12/C13 signature... the LHB was ~4.2-3.9 billion years ago)

So it should have had time to form before the LHB... and if it did... it had a good chance of surviving the LHB... so....

Why not 4 billion year old life?

It may be we'll never know precisely when life started, because there is almost nothing that is left that predates the LHB.

Of course, the LHB is not 100% settled either..

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Kryten

Kryten

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I am aware of the problems in the assumptions.

But the bigger problem is the assumptions in the evidence.

You can have the most precise dating that you want for a piece of evidence that is completely ambiguous...

We already have the case where above ground nuclear testing requires recalibration of dating methods for more recent events.

1.7 billion years ago, there were natural nuclear reactors on earth because U-235 (half life ~700 million years) was more abundant.

4 billion years ago, U-235 would be even more abundant... but we've got very little evidence from that time, and we don't now if there were earlier reactors, or how they might affect things.

You're acting like natural reactors are common. Getting the right physical conditions to moderate one is extremely unlikely, and we still only know of where locality where it actually happened.

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KerikBalm

KerikBalm

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Yes, its not common, but going back to over 4 billion years ago is going back roughly 3 half lives of U-235, which means the U-235 concentration would be roughly 8 times higher than it was then, and ~50-60 times higher than it is now.

I'm assuming that with 60x more concentrated U-235, it was relatively likely to happen somewhere during that time period.

According to wikipedia, it was less likely to have uranium ore deposits to form in an oxygen-less atmosphere... but I'm not qualified to comment on that.

Besides, the confirmed case happened when O2 was still at low concentrations in the atmosphere.. although it was there... it apparently happened around the transistion from "stage 2" to "stage 3" according to this graph.

840px-Oxygenation-atm-2.svg.png

Anyway... thats beside the point.

The date is more reliable than the C12/C13 ratio being evidence of life.

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