* Astronomy

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RE: Snowball Earth

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Even in geology, it's not often a date gets revised by 500 million years. But University of Florida geologists say they have found strong evidence that a half-dozen major basins in India were formed a billion or more years ago, making them at least 500 million years older than commonly thought. The findings appear to remove one of the major obstacles to the Snowball Earth theory that a frozen Earth was once entirely covered in snow and ice - and might even lend some weight to a controversial claim that complex life originated hundreds of million years earlier than most scientists currently believe.

'In modern geology, to revise the age of basins like this by 500 million years is pretty unique' - Joe Meert, a UF associate professor of geology.

Meert is one of eight authors of a paper on the research that recently appeared in the online edition of the journal Precambrian Research.
The Purana basins - which include the subject of the study, the Vindhyan basin - are located south of New Delhi in the northern and central regions of India. They are slight, mostly flat depressions in the Earth's crust that span thousands of square miles. For decades, most geologists have believed the basins formed 500 million to 700 million years ago when the Earth's crust stretched, thinned and then subsided.
Meert said that date may have originated in early radiometric dating of sediment from the basin. Radiometric dating involves estimating age based on the decay or radioactive elements. Additionally, apparent fossils retrieved from the basin seemed to have originated between 500 million and 700 million years ago.

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An abrupt release of methane, a powerful greenhouse gas, about 635 million years ago from ice sheets that then extended to Earths low latitudes caused a dramatic shift in climate, triggering a series of events that resulted in global warming and effectively ended the last snowball ice age, a UC Riverside-led study reports.
The researchers posit that the methane was released gradually at first and then in abundance from clathrates methane ice that forms and stabilizes beneath ice sheets under specific temperatures and pressures. When the ice sheets became unstable, they collapsed, releasing pressure on the clathrates which began to degas.

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An extraordinary episode of global cooling hundreds of millions of years ago that some experts say caused Earth to completely freeze over has been miscalculated, a new study says.
Instead of "Snowball Earth," the planet really became "Slushball Earth," its authors suggest.
The great chill -- the longest and deepest ice age in Earth's known history -- happened during the late Neoproterozoic era, 850 to 542 million years ago.
The evidence for the Snowball thesis comes from deep sediments in the ocean.
Scientists look through these layers to measure levels of the isotope carbon 13 (C13), deposited in plants through photosynthesis, as a telltale of Earth's climate.
Above and below the Cryogenian layer is an abundance of C13. But the Cryogenian layer itself has negligible levels of this isotope.
Coupled with other signs of intense glaciation, the explanation is that Earth froze over completely
One viewpoint suggests that the planet required millions of years to recover from these deep freezes--the last one occurring about 550 million years ago--and could do so only via the accumulation of atmospheric carbon dioxide from volcanic eruptions.
Now a team from the University of Toronto in Canada has used a model of the carbon cycle to show that the presence of the element--in the form of a class of minerals called carbonates--in the sea bottom arrested the deep freeze before it completely overcame the planet. Instead of snowball Earth, the team reports in the 6 December issue of Nature, the effect was more of a "slushball Earth."
The researchers, led by geophysicist W. Richard Peltier, found that cooling global temperatures allow the oceans to absorb more oxygen from the atmosphere. The oxygen reacts with carbonates deposited from the skeletons of tiny marine organisms as well as the action of photosynthesis by plankton, releasing carbon dioxide that helps temperatures bounce back quickly, at least on a geological timetable. The greenhouse effect has played an important role.

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Miracle Planet: Snowball Earth - Methane

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The theory that Earth once underwent a prolonged time of extreme global freezing has been dealt a blow by new evidence that periods of warmth occurred during this so-called 'Snowball Earth' era.
Analyses of glacial sedimentary rocks in Oman, published online today in Geology, have produced clear evidence of hot-cold cycles in the Cryogenian period, roughly 850-544 million years ago. The UK-Swiss team claims that this evidence undermines hypotheses of an ice age so severe that Earth's oceans completely froze over.
Using a technique known as the chemical index of alteration, the team examined the chemical and mineral composition of sedimentary rocks to search for evidence of any climatic changes. A high index of alteration would indicate high rates of chemical weathering of contemporary land surfaces, which causes rocks to quickly decompose and is enhanced by humid or warm conditions. Conversely, a low chemical index of alteration would indicate low rates of chemical weathering during cool, dry conditions.

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Ultrachron

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RE: Snowball Earth

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Our Ancestors survived 'Snowball Earth':
It has been 2.3 billion years since Earth's atmosphere became infused with enough oxygen to support life as we know it. About the same time, the planet became encased in ice that some scientists speculate was more than a half-mile deep. That raises questions about whether complex life could have existed before "Snowball Earth" and survived, or if it first evolved when the snowball began to melt.

New research shows organisms called eukaryotes -- organisms of one or more complex cells that engage in sexual reproduction and are ancestors of the animal and plant species present today -- existed 50 million to 100 million years before that ice age and somehow did survive. The work also shows that the cyanobacteria, or blue-green bacteria, that put the oxygen in the atmosphere in the first place, apparently were pumping out oxygen for millions of years before that, and also survived Earth's glaciation.
According to University of Washington astrobiologist Roger Buick, a professor of Earth and space sciences, the findings call into question the direst models of just how deep the deep freeze was. While the ice likely was widespread, it probably was not consistently as thick as a half-mile.

"That kind of ice coverage chokes off photosynthesis, so there's no food for anything, particularly eukaryotes. They just couldn't survive. But this research shows they did survive" - Roger Buick.

Buick and colleagues studied droplets of oil encased in rock crystals dating from 2.4 billion years ago, recovered from the Elliot Lake area near Sault Ste. Marie, Ontario, Canada. The oil, essentially chemicals left from the breakdown of organic matter, contained biomarkers, or molecular fossils, that can be structurally identified as having come from specific types of life.

"It's the same thing as looking at dinosaur fossils, except these fossils are at the molecular scale. You are looking at the molecular skeletons of carbon molecules, such as cholesterol, held within oil droplets" - Roger Buick.

This is not the first time biomarkers indicating that eukaryotes and cyanobacteria were alive before "Snowball Earth" has been found in ancient rocks. A paper reaching the same conclusion was hailed as one of the top science breakthroughs of 1999. Buick did some of the research for that paper and was a co-author. But almost from its publication, detractors have said what was seen were not really ancient biomarkers but rather some kind of contamination that got into the samples being studied, possibly from oil flowing through shale rocks at a much later time or modern fossil fuel pollution.

"The contamination idea has always been nattered about in corridors or talked about in meetings, but never put down in print. What this new paper does is confirm these as being very, very old biomarkers" - Roger Buick.

The lead author of the paper, published in the June edition of Geology, is Adriana Dutkiewicz of the University of Sydney in Australia, for whom Buick served as a postdoctoral mentor. Other authors are Herbert Volk and Simon George of the Commonwealth Scientific and Industrial Research Organisation in Australia and John Ridley of Colorado State University.
The researchers examined rock samples obtained from an outcrop near Elliot Lake, which then were fragmented into pieces less than one-tenth of an inch in diameter. The particles were cleaned thoroughly and checked for contamination throughout the process. The crystal fragments contained numerous minuscule pockets of fluid mostly consisting of water but also containing small amounts of oil, usually in a thin film around a bubble of water vapour. The oil resulted from decaying organic matter, probably of marine origin.

"A drop of oil is a treasure trove. It is highly concentrated molecular fossils" - Roger Buick.

The biomarkers contained in the oil indicate that both eukaryotes and cyanobacteria first appeared before the planetary glaciation, rather than evolving at the same time or later. The samples also suggest that oxygen was being produced long before the atmosphere became oxygenated, probably oxidising metals such as iron in the Earth's crust and ocean before the atmosphere began filling with oxygen.

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Many lines of evidence support a theory that the entire Earth was ice-covered for long periods 600-700 million years ago. Each glacial period lasted for millions of years and ended violently under extreme greenhouse conditions. These climate shocks triggered the evolution of multicellular animal life, and challenge long-held assumptions regarding the limits of global change.

The Snowball Earth hypothesis attempts to explain a number of phenomena noted in the geological record by proposing that an ice age that took place in the Neoproterozoic was so severe that the Earth's oceans froze over completely, with only heat from the Earth's planetary core causing some liquid water to persist under ice more than two kilometres thick. The general hypothesis has been around for several decades. Joseph Kirschvink, Professor of Geology at the California Institute of Technology coined the term "Snowball Earth" in 1992. The hypothesis has since been reformulated and championed by Paul F. Hoffman, Sturgis Hooper Professor of Geology at Harvard University and his colleague Daniel P. Schrag.

Since the 1960s, it has been hypothesised that the Earth's continents were subjected to severe glacial action between about 750 million and 580 million years ago, so much so that the period is named the Cryogenian Period. Later, palaeontologist W. Brian Harland pointed out that glacial till deposits of this period can be found on all continents, and first proposed that the Earth must have been in an ice age at this time. The problem is that the evidence-bearing deposits are found on all continents; but even during the worst of the ice age just past, no evidence of ice has been found in equatorial continents except on the higher parts of the highest mountain ranges. The then-new theory of plate tectonics made the oddly placed glacial discontinuities and deposits of glacial till even more enigmatic: studies of the magnetic orientations of the rocks of the late Proterozoic period showed that the continents were clustered around the equator during at least the start of the corresponding time around 750 million years ago— in one of the earliest of the configurations known as supercontinents. This equatorial clustering and collision of continents about 750 million years ago has been named Rodinia; it being near the equator, rather than near the poles as might have been expected, taken together with thermal evidence of a severe ice age 750 to 635 million years ago (the dating suggested by the widespread geologic deposits) is what has led to the Snowball Earth theory.

The Snowball Earth theory argues from the documented locations of glacial till dropped by these glaciers, to suggest that the Earth must have completely frozen over. The mechanism by which it did so is still mysterious. One suggestion is that normally, as the ice spread, it would cover some of the land, and so slow the carbon dioxide absorption, and so increase the greenhouse effect, as volcanoes continue to emit carbon dioxide, and the ice spread would stop; but with all the continents clustered along the equator, this would not happen until the freezing process had run away. Once frozen, the condition would tend to stabilise: a frozen earth has a high albedo, reflecting more of the sun's radiation, and a frozen earth, with reduced evaporation, has a very dry atmosphere, water vapour being one of the greenhouse gases. A "Snowball Earth" would have a blindingly clear blue sky above its reflective surface.

The mechanism by which the Earth would unfreeze — as it must have done if it froze—would leave distinctive traces, which are the subject of ongoing research.

White Earth is a name given to a theoretical equilibrium found in computer climate simulations whereby the model Earth undergoes complete glaciation. While this seems to have originally been considered a degenerate case by the time James Gleick wrote his history of chaos theory Chaos: Making A New Science, it was not dismissed in his book but simply restated as something that probably just had not happened yet. The current evidence for the Snowball Earth would seem to back that theory and its computer models.

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