Wow, it's a bonzer edition of
Nature this week! In addition to the bits I've just put in <a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=58&t=000424" target="_blank">Scigirl's thread</a>, this deserves its own thread I think.
From Nature Science Update:
"<a href="http://www.nature.com/nsu/020304/020304-6.html" target="_blank">Earliest life or rare dirt?</a> Gloves are coming off in ancient bacteria bust-up."
Quote:
The one thing both parties agree on is that only time will tell. Schopf is continuing to analyse his putative fossils. A nanoscale examination of their 'cell membranes' will, he claims, prove beyond doubt that the Apex chert does contain the oldest known remains of life on Earth.
Brasier and his team are now investigating the kind of chemical reactions that they believe produced the squiggles. The researchers suspect the reactions could themselves have created complex molecules such as amino acids and be the source of life on Earth. "Schopf may have stumbled on a site that may explain how life got started," says Brasier.
[My emphasis]
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Here’s from
New Scientist. As it’s a ‘news’ item, and I don’t think these stay online long, here’s the whole thing:
Quote:
Tiny fossils may be Earth's oldest life
A fierce debate over tiny imprints in ancient terrestrial rock could rewrite the textbooks on the early evolution of life on Earth.
At issue are microscopic patterns of filaments embedded in 3.5-billion-year-old rock from Western Australia. William Schopf of UCLA, who first described them over a decade ago, says they represent 11 different bacterial species, including photosynthetic cyanobacteria. This would make them the oldest fossils ever found.
A similar debate has raged over the minute structures found in the famous Martian meteorite ALH84001.
Schopf has now studied the Australian rocks using a technique called laser Raman analysis, which involves bouncing a laser beam off the rock surface. This produced a scattering pattern identical to that created by organic molecules found in other fossils. Schopf is convinced this proves his case.
High-speed evolution
If he is right, early life must have diversified incredibly quickly. The first bacteria are thought to have been "chemotrophic" species that lived in the dark near underwater hydrothermal vents, feeding on chemicals released there.
For a range of photosynthetic species to have evolved as early as 3.5 billion years ago, the first life must have appeared almost as soon as the last asteroid bombardment ceased 3.9 billion years ago, and then evolved rapidly. That suggests life may also have had time to evolve on a young, wet Mars.
But challengers of this view, led by Martin Brasier of Oxford University, say the imprints Schopf found have no direct connection to life. They claim the rock containing the fossils is actually volcanic glass from a hydrothermal vent that formed tens of metres under water - too deep for photosynthetic bacteria to live. When the melted rock recrystallised, organic contaminants got rearranged to look like cells.
That would imply life took much longer to get started. According to Brasier, the first clear evidence of cyanobacteria is just 2.7 billion years old, while the diversity of species that Schopf claims to have found did not appear until 2.1 billion years ago.
Most early life researchers take a view between the two extremes. Jack Farmer of Arizona State University thinks Schopf's objects are fossils, but he is not convinced they are cyanobacteria. He says they could be chemotrophic bacteria from hydrothermal vents, similar to the earliest forms of life. If that is the case, life need not have diversified quite so fast after all.
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Here’s the original abstracts:
Nature 416, 73 – 76, 7 March 2002
Quote:
Laser–Raman imagery of Earth's earliest fossils
Schopf et al
Unlike the familiar Phanerozoic history of life, evolution during the earlier and much longer Precambrian segment of geological time centred on prokaryotic microbes. Because such microorganisms are minute, are preserved incompletely in geological materials, and have simple morphologies that can be mimicked by nonbiological mineral microstructures, discriminating between true microbial fossils and microscopic pseudofossil 'lookalikes' can be difficult. Thus, valid identification of fossil microbes, which is essential to understanding the prokaryote-dominated, Precambrian 85% of life's history, can require more than traditional palaeontology that is focused on morphology. By combining optically discernible morphology with analyses of chemical composition, laser–Raman spectroscopic imagery of individual microscopic fossils provides a means by which to address this need. Here we apply this technique to exceptionally ancient fossil microbe-like objects, including the oldest such specimens reported from the geological record, and show that the results obtained substantiate the biological origin of the earliest cellular fossils known.
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And then on pages 76 – 81:
Quote:
Questioning the evidence for Earth's oldest fossils
Brasier et al
Structures resembling remarkably preserved bacterial and cyanobacterial microfossils from 3,465-million-year-old Apex cherts of the Warrawoona Group in Western Australia currently provide the oldest morphological evidence for life on Earth and have been taken to support an early beginning for oxygen-producing photosynthesis. Eleven species of filamentous prokaryote, distinguished by shape and geometry, have been put forward as meeting the criteria required of authentic Archaean microfossils, and contrast with other microfossils dismissed as either unreliable or unreproducible. These structures are nearly a billion years older than putative cyanobacterial biomarkers, genomic arguments for cyanobacteria, an oxygenic atmosphere and any comparably diverse suite of microfossils. Here we report new research on the type and re-collected material, involving mapping, optical and electron microscopy, digital image analysis, micro-Raman spectroscopy and other geochemical techniques. We reinterpret the purported microfossil-like structure as secondary artefacts formed from amorphous graphite within multiple generations of metalliferous hydrothermal vein chert and volcanic glass. Although there is no support for primary biological morphology, a Fischer–Tropsch-type synthesis of carbon compounds and carbon isotopic fractionation is inferred for one of the oldest known hydrothermal systems on Earth.
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So, um, there.
Cheers, Oolon
[ March 13, 2002: Message edited by: Oolon Colluphid ]</p>
03-13-2002, 03:47 AM
Earliest life or rare dirt?
