* Astronomy

UK scientists have traced the history of wildfires by studying lumps of ancient charcoal from around the world.
The fossils show the incidence of fires through time is closely related to the level of atmospheric oxygen.
Andrew Scott and Ian Glasspool say huge swathes of the planet were ablaze when concentrations of the gas peaked some 275 million years ago.

Scott and Glasspool, who is affiliated to Chicago's Field Museum, examined charcoal residues preserved from about 440 to roughly 250 million years ago.
It covers the period when scientists believe plants first got a strong foothold on land and spread rapidly across the surface.
The charcoal samples studied came from all around the world, including the US, Australia, Scotland, India, Norway, South Africa and Antarctica.
The researchers examined the material to ascertain the types of fires that produced the charcoal and their likely incidence. They then compared this with models other scientists have produced to describe how oxygen in Earth's atmosphere is thought to have changed over time.
There appears to be a strong link.
The team found that fires were rare and localised for the first 50 million years of plant evolution but then they increased in frequency as the levels of oxygen in the atmosphere rose.
From around 365 million years ago, severe fires became widespread across the planet. Oxygen levels peaked at 30% 275 million years ago, in comparison with only 21% today. In this period even damp vegetation would have ignited easily causing many more fires.

Their research is published in the US scientific journal Proceedings of the National Academy of Sciences.

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This picture is a composite of images of the Strelley Pool Chert rock formation in in the Pilbara region of Western Australia. It was acquired by the Landsat-7 satellite on May 19, 2000 (in the north), and June 23, 2001 (in the south). The Pilbara region sees hot temperatures and little rain, and its terrain is rugged, evidenced by the many creases and networks of hills meandering through the area. The Shaw River channel runs through the middle of the image. The Strelley Pool Chert rock formation appears near the bottom of the image, on the east side of the river.


(91kb, 560 x 430)
Credit NASA
Latitude -21.271993° Longitude 119.299398°

The rocks of the Strelley Pool Chert preserve an environment that existed 3.43 billion years ago, including several kinds of stromatolites. Palaeontologists and geologists conclude that this area was once submerged under the ocean and formed a fairly flat area, perhaps the floor of a shallow ocean. As this now-arid region was once underwater, stromatolite-forming microbes would have thrived in a shallow sea where the water kept them moist but the Sun’s rays could still penetrate and fuel photosynthesis.

Stromatolites have traditionally been defined as remains of ancient life forms—microbial mats that mixed with mud and built up rock-like structures—and this interpretation is bolstered by the existence of modern stromatolites that now live along the coast of Western Australia. The fossils of the actual microbes are rarely preserved, however, and studies with computer models have suggested that sediment could accumulate in similar ways without the aid of any living thing. In other words, these studies raised questions about whether stromatolites are actual fossils. A 2006 Nature paper, however, added weight to the microbial interpretation. The paper described several different kinds of stromatolites in the Strelley Pool Chert, such as big domes, big cones, little cones, waves, and even shapes looking like giant egg cartons. The paper’s authors argued that the diversity of stromatolites found there are too complex to derive purely from sedimentary processes. Although many researchers expected the debate about the nature of stromatolites to continue, this paper concluded that microbes would have been necessary to build such varied shapes.

-- Edited by Blobrana at 08:23, 2006-06-18

Odd-shaped rocks in the Pilbara region of Western Australia offer compelling evidence they were built by microbes 3.43 billion years ago, scientists say.

The structures, known as stromatolites, could only have taken the forms they have if bacteria had been present, a Sydney-led team tells Nature journal.
The rocks' origin is disputed, with some claiming purely chemical processes could have made them.
But the Nature study suggests the biological explanation is the simplest.

"For all these shapes to be formed a-biologically would have required highly unusual and unexpected chemical processes to occur simultaneously in this (one location). It just becomes ridiculous to support that hypothesis; especially when the biological explanation is so readily acceptable" - Abigail Allwood from the Australian Centre for Astrobiology.

Ms Allwood and colleagues have made an extensive survey of a 10km stretch of land not far from the town of Marble Bar.
The area is now well inland but shows clear evidence of having been covered by a shallow sea in the ancient past.
The researchers have detailed an array of unusual sedimentary structures - seven clear types in all. Some look like upside-down ice cream cones; others resemble egg cartons.
These laminated structures have been described as stromatolites - the rock piles that in more recent settings are known to have been built by mats of microbes capturing grains and sticking them together.
But the Pilbara structures, found 30 years ago in a rock formation called the Strelley Pool Chert, are controversial.
Claims for individual microfossils of the original organisms within Pilbara's stromatolites have been challenged; and some scientists prefer an entirely non-biogenic explanation for the structures' creation.
These dissenters believe the piles resulted from the chemical precipitations that occurred around undersea volcanic vents.

Allwood's response has been to describe the complexity of shapes and explain how these forms can be linked to different environmental niches in a shallow-sea reef setting.

"We have found an ecosystem-scale remnant of the early biosphere. It's not just a couple of individual or isolated fossils or dubious structures; it is in an entire, pretty well intact, section of hundreds of thousands of stromatolites in a reef ecosystem. With that we now gain insight into the conditions that nurtured early life - the biological responses to different environmental processes" - Abigail Allwood.

The Pilbara stromatolites are not the oldest claim for life on Earth.
Some researchers argue that rocks at Isua in Greenland show the imprint of life at least 3.75 billion years ago.
At that time, these rocks were also on the sea bed. Thin layers of black sediment, separated by distinct layers of volcanic ash, look like they could be composed of the debris of ocean-dwelling microbes.
There are no fossil forms, but the nature of the carbon is consistent with the idea it was processed by living organisms. There are no known older remnants of the Earth's surface than the Greenland rocks - which probably makes Isua the closest science can ever get to the first life.
Researchers are keen to trace the story of the first microbes on Earth because it should provide clues in the hunt for possible life elsewhere in the Solar System.
The type of study conducted on the Pilbara stromatolites might, for example, help scientists interpret similar structures on Mars, should rovers sent to the planet ever come across them.

"Searching for ancient stromatolite-like structures such as those reported by Allwood et al should certainly be high on the list of future exploration strategies. However, given the amount of fieldwork performed by Allwood and colleagues, it must be doubtful whether purely robotic exploration of Mars would be able compellingly to identify such features in the field, and in the longer term effective Martian palaeontology my necessitate human exploration of the planet" - Dr Ian Crawford, a planetary scientist at Birkbeck College, London, UK.

Source BBC

Two laboratories at Penn State set out to show how an obscure undersea microbe metabolises carbon monoxide into methane and vinegar. What they found was not merely a previously unknown biochemical process--their discovery also became the inspiration for a fundamental new theory of the origin of life on Earth, reconciling a long-contentious pair of prevailing theories. This new, "thermodynamic" theory of evolution improves upon both previous theories by proposing a central role for energy conservation during early evolution, based on a simple three-step biochemical mechanism.

Their results also provide insights into the evolution of the microbial production of methane, the primary component of natural gas. A detailed understanding of methane biosynthesis could lay the foundation for a new alternative energy source, by raising the possibility of cost-efficient conversion of renewable biomass into clean fuel.
James G. Ferry is Stanley Person Professor of Biochemistry and Molecular Biology, and Christopher House is Assistant Professor of Geosciences, both at Penn State. They will announce their new theory in the June issue of Molecular Biology and Evolution.

"The paper is a very significant contribution, and a wonderful example of interdisiplinary work as well." - William Martin, editor-in-chief of that journal.

"We've taken a new approach to thinking about the evolution of life from a thermodynamic perspective. It reshapes the two previous theories of life's origin, it shows how they overlap, and it extends both of them significantly" - James G. Ferry.

The apparently irreconcilable "heterotrophic" and "chemoautotrophic" theories of the origin of life both focus on the processes by which chemical building blocks first appeared for primitive life to assemble into complex molecules.

"But that's not really what the driving force was in early evolution. Nobody had properly considered thermodynamics" - James G. Ferry.

"The problem of early energy sources has largely been ignored by the classical origin-of-life field, which has largely been the domain of chemists. But microbiologists are the only ones who understand where the origin of life needs to get--modern microbial life" - William Martin.

According to the heterotrophic theory, a primordial soup of simple molecules arose first, driven by nonbiological energy sources like lightning, and led eventually to primitive life forms. One difficulty with this theory is due to the huge variety and complexity of organic molecules that would have had to arise spontaneously. In contrast, the chemoautotrophic theory rests on the idea that primitive life forms themselves, perhaps associated with catalytic iron and sulphur minerals, gave rise to the first simple biological molecules. The obstacles to this theory are the large number of steps in the biochemical cycles that have been suggested, and the staggering structural complexity of the only known enzyme complexes that drive those reactions. Debate between the two camps has raged for two decades.
By studying a microbe that Ferry discovered thriving in the oxygen-free, carbon-monoxide-rich sediment beneath kelp beds, he and his group have helped to break this impasse. Life may have emerged in just such an environment, and this microbe's unique biochemistry may harbour the molecular fossil of the first metabolism on Earth.
While other microbes make methane from carbon monoxide, this particular species (one "Methanosarcina acetivorans") also produces acetate--better known as vinegar. Ferry and House, in collaboration with Barry Karger at Northeastern University, showed how carbon monoxide is converted to acetate in a biochemical pathway that includes a well-known pair of enzymes, called Pta ("phosphotransacetylase") and Ack ("acetate kinase"). The two researchers realized that, in the presence of minerals containing iron sulfides, acetate could have been catalytically converted to a sulphur-containing derivative called an acetate thioester. Attached to the mineral surface, a "protocell" containing primitive forms of these two enzymes could then have generated biochemical energy by converting this derivative back to acetate. Excreting acetate would have completed the cycle.

"Our paper contains a very sensible early metabolism"- Christopher House.

"It is quite possible that this could be the first metabolic cycle" - James G. Ferry.

As in virtually every metabolic reaction on Earth, the energy produced by these reactions is stored in a molecule called ATP. The Ack enzyme catalyses the synthesis of ATP directly. On the other hand, most ATP molecules--including those that this microbe makes by converting carbon monoxide into methane--are produced by multi-enzyme protein machines within the cell membrane that get their energy indirectly, from yet another protein machine that pumps an osmotic imbalance across the membrane.

"It's difficult to imagine that something so complex could have emerged all at once" - James G. Ferry. (as the chemoautotrophic theory requires).

The acetate-producing species appears to be the direct descendant of one of the earliest true microbes.

"We know that this bug is very ancient indeed. There is strong phylogenetic evidence that acetate kinase is a very ancient enzyme" No such evidence can pinpoint the age of Pta, "but these two enzymes always work together" suggesting that they evolved together. The two enzymes' primeval genetic provenance and the simplicity of the three-step cycle, "are absolutely central to the idea. This longstanding debate between the heterotrophic and chemotrophic theories revolved around carbon fixation"- Christopher House.

"The new thermodynamic theory inverts the focus. All these pathways evolved first to make energy. Afterwards, they evolved to fix carbon. These ideas suggest a totally new perspective. It's truly a quantum leap--a milestone"- James G. Ferry.

The paper also proposes mechanisms by which Ferry and House's mineral-bound protocell could have evolved into a free-living cell, and how the metabolism of acetate to methane could have evolved based on the pathways they discovered. The genomic and proteomic analyses of carbon monoxide conversion to methane and acetate, carried out in collaboration with Northeastern's Karger, will appear later this year. The Department of Energy and the NASA Astrobiology Institute sponsored the research.

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