The Loom

In the Beginning Was the Borehole

There are only a few places on the surface of Earth where you can find really old rocks–and by old, I mean 3.5 billion years old or older. The rest have gotten sucked down into the planet’s interior, cooked, scrambled with other rocks, and pushed back up to the growing margins of continental plates. The few formations that have survived are mere fragments, some the size of a football field, some a house. And generally they’re are mess, shot through with confusion such as intrusions of lava from more recent volcanoes. Paleontologists are drawn and repulsed by these rocks, because they may hold the oldest clues about life on Earth, or lifeless mirages that only look like clues.

In the past couple years, scientists have been putting the oldest evidence of life on Earth under tough scrutiny. The oldest fossils, 3.45 billion year old bacteria from Western Australia, have been attacked as mere crud. Life not only leaves fossils behind but also can create peculiar ratios of isotopes in rocks. The oldest isotopic evidence for life came from 3.8 billion year old rocks in Greenland. But that also came under attack by critics who questioned whether the rocks were actually sedimentary (and thus might contain biological material) or belched up from a very nonbiological volcano.

This does not mean that the fossil record has collapsed down to yesterday’s road kill. In other parts of Greenland, scientists have found slightly younger rocks (if you can call 3.7 billion year old rocks young) that are almost certainly sedimentary. And they contain a clear isotopic signature of life. The Danish geologist Minik Rosing, who has studied the rocks, argues that this particular fingerprint is so detailed he can tell what kind of life produced it: photosynthesizers. That’s tantalizing for several reasons. One is that photosynthesizers give off oxygen, and yet there’s no record of any signifciant levels of oxygen in the atmosphere for well over a billion years after Rosing’s rocks formed. Another is that the early Earth may not have been a very friendly place for photosynthesizers—the oceans were hot and loaded with nasty metals.

The controversy over ancient fossils has forced some paleontologists to look for new kinds of evidence of life. For example, some bacteria can eat through glass, leaving behind microscopic pits. Volcanoes form glassy rocks such as obsidian, and in recently formed volcanic rocks sicentists have found tunnels that seem to have been created by hungry microbes. (They’re even slathered with DNA and other biological material.). Today in Science, researchers reported that 3.5 billion year old rocks from Zimbabwe bear the same sorts of tunnels. They’re also slathered in organic carbon with an isotopic fingerprint that looks like life. The evidence has impressed some researchers, but others are still skeptical. The possibility that these formations are formed without the help of microbes hasn’t been eliminated yet.

I find all this work fascinating, but in one fundatmental way it’s a bit pedestrian. These scientists are looking for the earliest signs of organisms that resemble organisms alive today, looking for the traits that are common to both. But a photosynthetic or glass-chewing bacterium is already pretty nicely evolved. Someday, a clever paleontologist is going to figure out how to identify something that no longer exists on Earth, such as an RNA-based organism. That discovery will push the fossil record back to a different chapter altogether in the book of life.

Comments

  1. #1 Paul Orwin
    April 23, 2004

    Just a quick note. While the tantalizing thought of oxygenic photosynthesis may appeal, it is very certain that the first photosynthetic pathways were non oxygenic. These are still present in modern day bacteria such as the purple phototrophs (eubacteria, phylum proteobacteria). The oxygenic photosynthesis (also called non-cyclic photophosphorylation) probably arose somewhat later, maybe 1.5-2 bya, in the bacterial groups that descended to the cyanobacteria.

  2. #2 comgelo
    April 26, 2004

    Best regards from Portugal:-)

  3. #3 shiva pennathur
    April 27, 2004

    One of the responses of scientists to I pseudoscientific assertions that irritates me is, “Evolution is not about the origin of life, it is about its change” Stop! Well evolution WAS about change of life forms some 100 years ago. Since then it has come to offer a direction of enquiry across all disciplines of science as it is practiced today (I hate to use that overused hack Paradigm). Evolutionists (inapt as the term is) are interested in the OOL and what happened in the earliest mists of time on earth does have something to do with how evolution works today – protein origin, self-replicators etc. I wish scientists would stop making this annoying response and instead say something like, “Baloney. The research on OOL has been going on for over 65 years. Here are the names of over a 100 scientists, a list of over 10,000 papers, and over 75 projects current. Your objections count for nothing. If you want to raise them still talk to me after you have read the literature.”

  4. #4 Fz+
    April 27, 2004

    Shiva, idealistic as that may be, it doesn’t work in practice. Doing this opens up a wide variety of unproductive arguments. I’ve seen people mount a sort of last stand by insisting that ‘progressive random effects’ (ie. evolution) cannot occur in nature. When I try to give examples, I discover that progressive = precise set of steps that create current life. (Somehow, convection cells appearing to best fit the environment doesn’t count.) It is harder to make clear the important point that yes, evolution means nothing has to happen exactly that way, since the different alternative ways are apparently so hugely different as to be unrecognisible.

    The big problem is the difficulty in defining life. Pseudoscientists almost always have a irreducible, unfalsifiable ‘life force’, or ‘spirit energy’, or whatever, which serves no use but as a completely opaque barrier to evolutionary theory. In essence, they have made evolution incapable of explaining life, by definition.

  5. #5 shiva pennathur
    April 29, 2004

    It is interesting to see how little antievolution thought has progressed over the last 200 years. The pseudoscoentists still seem to think that life can be created by simply tossing a few chemicals into a test-tube and shaking and swirling it a little – Voila! a few living cells etc emerge. The pivot of the anti-evolution argument is that such a thing can be done only by God – because of his supernatural powers – and not by a scientist. It’s all horribly mixed up

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