Scientists find 3.7B-year-old fossil, oldest yet | Hacker News Reader

Scientists find 3.7B-year-old fossil, oldest yet

phys.org

136 pointsCozumel39 comments

In a related bit of paleogeology, a large share of iron ore, particularly banded iron formations (BIF) date from about this time -- they're typically about 1.2 - 3.7 billion years old, and date to the periods of early life, a large amount of free molecular (unoxidised) iron, a methane atmosphere, and early cyanobacteria whose metabolic waste product was oxygen. This combined with free dissolved iron in early oceans, precipitated out as iron oxides, and left the deposits now mined for ores. Exhaustion of the dissolved iron resource lead to a rise in atmospheric oxygen (poisonous to the cyanobacteria), a depletion of the methane which served to warm the Earth under the light of a much cooler sun, and resulted in a half-billion year "Snowball Earth" period -- an earlier form of overzealous biological organisms triggering catastrophic environmental pollution and climate change.

I find it fascinating to think about how and where minerals came from (iron originates in stellar fusion, it's the low point of the atomic potential curve, and hence you cannot fuse nor fission iron nuclei to release energy), and how they came to be organised in deposits. Many minerals are concentrated through prior biological activity -- iron, limestone, and of course, coal and petroleum.

https://en.m.wikipedia.org/wiki/Banded_iron_formation

(Edit: Corrected erronious initial explanation of iron deposition -- precipitation, not biological binding.)

The discoverer of the previous oldest fossil (3.48B years) suggests that this find may not be organic in origin. Would be nice if other experts had been interviewed on that possibility, since there could potentially be some bias there.

Edit: perhaps "organic" was a poor choice of words. My meaning was that she disputed the claim that the artifact is in fact a fossil created by life, and suggested that it might be a geological formation of some sort instead.

I am not sure what the relevance would be. Are you using the term "organic" as in biological, or as in carbon-based?

In either case, what would it mean if it wasn't organic?

I believe tempestn is referring to the end of the article, where the scientist who found the previously oldest fossil says it may not actually be a fossil:

The dating seems about right, said Abigail Allwood, a NASA astrobiologist who found the previous oldest fossil, from 3.48 billion years ago, in Australia. But Allwood said she is not completely convinced that what VanKranendonk's team found once was alive. She said the evidence wasn't conclusive enough that it was life and not a geologic quirk.

"It would be nice to have more evidence, but in these rocks that's a lot to ask," Allwood said in an email.

Right, yes. I don't know anything about this person, but certainly there are people out there who would be biased against having their little place in history overshadowed by a new discovery, perhaps even unconsciously. Not saying she is biased, just that it would be nice to see the opinions of some other experts, not involved in the discovery.

In fact, even if it were a completely unbiased third-party opinion it would still be nice to have more than one, since as a lay-person I'm currently left with no idea how likely it is that this is in fact evidence of early life.

In the article the term "organic" isn't used at all:

  > The dating seems about right, said Abigail Allwood , a NASA
  > astrobiologist who found the previous oldest fossil, from
  > 3.48 billion years ago, in Australia. But Allwood said she is
  > not completely convinced that what VanKranendonk's team found
  > once was alive. She said the evidence wasn't conclusive enough
  > that it was life and not a geologic quirk.
  > 
  > "It would be nice to have more evidence, but in these rocks
  > that's a lot to ask," Allwood said in an email.

While it has already been cleared out, I would just like to point to this, from wiktionary:

  organic ‎(comparative more organic, superlative most organic)

    1. (biology) Pertaining to or derived from living organisms.

"cleared up", but yes, this is exactly what I took from OP's use of the term 'organic'.

I suppose I was hopeful that it was silicon based life :)

That previous fossil-finder (Abigail Allwood) wrote the overview article (http://www.nature.com/nature/journal/vaop/ncurrent/full/natu...) introducing the Nature paper that is the subject of the OP. Her overview emphasizes the significance of this finding for exo-life, linking the finding to recent discoveries of ancient water, lakes, and streamflows on Mars, rather than the caveats.

The more general news-based article in Nature (http://www.nature.com/news/claims-of-earth-s-oldest-fossils-...) has several experts checking in with caveats.

Perfect, thanks.

Or perhaps made from some strange matter, alien to understanding? (What does a fossilized Great Old One look like, anyway? Would it still be alive?)

As a little context, the oldest known minerals on Earth are a 4.4 billion-year-old and Earth itself is 4.543 billion years-old.

Can someone explain me how do they determine the age?

Carbon dating

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

https://www.boundless.com/biology/textbooks/boundless-biolog...

No, carbon-14 dating doesn't even reliably hit 1 million years ago, let alone 3 billion.

Edit: Even your Wiki link cites 500,000 years.

According to that boundless.com link, "The half-life of carbon-14 is 5,730 years, so carbon dating is only relevant for dating fossils less than 60,000 years old."

But from the Wikipedia about radiocarbon method: "Radiocarbon dating is a radiometric dating method that uses (14C) to determine the age of carbonaceous materials up to about 60,000 years old."

The most well-known way of determining fossil age is carbon dating[0].

[0] http://science.howstuffworks.com/environmental/earth/geology...

Using radiogenic isotope geology.

Carbon dating only works on very recent things (up to a few tens of thousands of years). For older things like the earth and these fossils, slower-ticking radiometric clocks (like Uranium-Lead clocks) must be used. There was a great COSMOS episode discussing the history of it [1] but the fascinating math and science behind it is better explained for the layperson in [2].

[1] http://channel.nationalgeographic.com/cosmos-a-spacetime-ody...

[2] https://whatisnuclear.com/physics/age_of_earth.html

>"Carbon dating only works on very recent things"

Ironically, it doesn't work well at all for dating very recent objects though, at least without a huge fudge factor that could only be applied if very specific info is available: https://en.wikipedia.org/wiki/File:Radiocarbon_bomb_spike.sv...

There are other dating techniques that use trace radioactive elements from nuclear bomb testing that have accumulated in living organisms.

http://www.sciencedirect.com/science/article/pii/S0092867405...

Well, I meant very recent in the geological sense ;)

Good calibration curves accounting for things like that in your link are definitely required to get modern-era results, and with a 5,730 year half-life, it's difficult to even make meaningful measurements to throw onto the curve. So you're right.

Magic... AKA "Scientific guessing" Seriously. Radiometric dating is about as reliable as guessing based upon how dirty it is.

There are some very reliable ones. C14 is based on isotope ratios and is kind of crap, but uranium-lead dating is much less ambiguous because of chemical differences between uranium and lead.

I suppose there are more accurate ways, but we still have to do some guesswork. I prefer skepticism over supposition.

This article lists 16 methods

https://en.m.wikipedia.org/wiki/Geochronology

Some fill,the gap between radio carbon and longer lived isotopes.

The used U-Pb dating of zircons. They did not date the fossil directly, instead they dated other rocks in the same stratigraphic sequence (Isua supracrustal belt). The relevant sentences:

The stromatolite discovery locality (Extended Data Fig. 1) is within the hinge of an anticline cored by 3,709 ± 9-Myr-old andesitic metavolcanic rocks with locally preserved pillow structures and a maximum metamorphic temperature of ~550 °C17, 18. The pillowed metavolcanic rocks are overlain by bedded dolomite-rich metasedimentary rocks and in turn, by interlayered quartzites and metamorphosed banded iron formation that contain rare, small, high Th/U oscillatory-zoned volcano-sedimentary zircons with ages of 3,699 ± 12 and 3,691 ± 6 Myr3, 18.

That means rocks with zircons dated to 3709 Ma are interpreted to be below (older) and rocks with 3699 Ma zircons are interpreted as being above (younger).

Zircon is an excellent mineral for geochronology as it contains U and Th. Two U isotopes, 235U and 238U, plus 238Th all decay to Pb at different rates (half lives). Zircon forms by growing from magma, and does not contain any Pb when grows, as Pb does not fit into the crystal structure, so any Pb you measure in a zircon today is from radiogenic decay of U and Th. If the ratios of the individual U and Th isotopes and their respective Pb daughter products are all consistent with the same age, i.e. you get the same age when you back calculate to zero Pb for all three isotope systems, then you can be very confident in the date, hence the small uncertainties on the reported dates from the paper.

Side note: Interesting paper on mathematical model often used in analyzing the patterns in stromatolites and other growing interfaces: the Kardar–Parisi–Zhang equation.

"Pattern formation in stromatolites: insights from mathematical modeling" http://rsif.royalsocietypublishing.org/content/9/70/1051

FWIW, Ed Yong:

  The newly discovered rocks suggest that life arose very
  quickly after the Earth was formed.

http://www.theatlantic.com/science/archive/2016/08/the-world...

3.5 billion years ago the skies were orange, the oceans were green and the land was black.

And men were men, and women liked it!

OK, maybe I should have gone with, "And men were real men, women were real women, and small, furry creatures from Alpha Centauri were real small, furry creatures from Alpha Centauri."

It was a true iron age.

Do you have any refs on the Earth's appearance at the time?

It's at the bottom of TFA. First I've seen it, too.

Ah, missed that, thanks.

Robert Hazen recent book on Earth assigns a distinctive color to each major geologic era- red, black, blue, green, white ...

hail helix

They measured a foot and the head of a mammoth to magnitudes of difference already.

You can't measure stuff that old. They almost decide how old they want it to be.

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