* Astronomy

Study Offers Clues to What Happened Prior to 'Snowball' Earth

In a study published in the journal Geology, scientists at the University of Miami suggest that significant changes in the carbon isotopic composition of carbonates, which occurred prior to the major climatic event (Snowball Earth) of more than 500 million years ago, are unrelated to worldwide glacial events.

"Our study suggests that the geochemical record documented in rocks prior to the Marinoan glaciation, or Snowball Earth, are unrelated to the glaciation itself. Instead, the changes in the carbon isotopic ratio are related to alteration by freshwater as sea level fell" - Peter Swart, professor of marine geology and geophysics at UM's Rosenstiel School of Marine and Atmospheric Science and co-author of the study.

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Research shows how life might have survived 'snowball Earth'

Global glaciation likely put a chill on life on Earth hundreds of millions of years ago, but new research indicates that simple life in the form of photosynthetic algae could have survived in a narrow body of water with characteristics similar to today's Red Sea.
A long, narrow body of water such as the Red Sea, about 6.5 times longer than it is wide, would create enough physical resistance to advancing glacial ice that the ice sheet likely could not make it all the way to the end of the sea before conditions cause the ice to turn to vapour. That would leave a small expanse of open water where the algae could survive.
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Title: A carbon isotope challenge to the snowball Earth
Authors: P. Sansjofre, M. Ader, R. I. F. Trindade, M. Elie, J. Lyons, P. Cartigny
& A. C. R. Nogueira

The snowball Earth hypothesis postulates that the planet was entirely covered by ice for millions of years in the Neoproterozoic era, in a self-enhanced glaciation caused by the high albedo of the ice-covered planet. In a hard-snowball picture, the subsequent rapid unfreezing resulted from an ultra-greenhouse event attributed to the buildup of volcanic carbon dioxide (CO2) during glaciation. High partial pressures of atmospheric CO2 (;from 20,000 to 90,000 p.p.m.v.) in the aftermath of the Marinoan glaciation (~635 Myr ago) have been inferred from both boron and triple oxygen isotopes. These values are 50 to 225 times higher than present-day levels. Here, we re-evaluate these estimates using paired carbon isotopic data for carbonate layers that cap Neoproterozoic glacial deposits and are considered to record post-glacial sea level rise1. The new data reported here for Brazilian cap carbonates, together with previous ones for time-equivalent units provide estimates lower than 3,200 p.p.m.v. - and possibly as low as the current value of ~400 p.p.m.v. Our new constraint, and our re-interpretation of the boron and triple oxygen isotope data, provide a completely different picture of the late Neoproterozoic environment, with low atmospheric concentrations of carbon dioxide and oxygen that are inconsistent with a hard-snowball Earth.

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Caltech-led Team Debunks Theory on End of "Snowball Earth" Ice Age

Finds that rocks used as key geologic evidence were formed deep within Earth millions of years after the ice age ended

There's a theory about how the Marinoan ice age - also known as the "Snowball Earth" ice age because of its extreme low temperatures - came to an abrupt end some 600 million years ago. It has to do with large amounts of methane, a strong greenhouse gas, bubbling up through ocean sediments and from beneath the permafrost and heating the atmosphere.
The main physical evidence behind this theory has been samples of cap dolostone from south China, which were known to have a lot less of the carbon-13 isotope than is normally found in these types of carbonate rocks. (Dolostone is a type of sedimentary rock composed of the carbonate mineral, dolostone; it's called cap dolostone when it overlies a glacial deposit.) The idea was that these rocks formed when Earth-warming methane bubbled up from below and was oxidised - "eaten" - by microbes, with its carbon wastes being incorporated into the dolostone, thereby leaving a signal of what had happened to end the ice age. The idea made sense, because methane also tends to be low in carbon-13; if carbon-13-depeleted methane had been made into rock, that rock would indeed also be low in carbon-13. But the idea was controversial, too, since there had been no previous isotopic evidence in carbonate rock of methane-munching microbes that early in Earth's history.
And, as a team of scientists led by researchers from the California Institute of Technology (Caltech) report in this week's issue of the journal Nature, it was also wrong - at least as far as the geologic evidence they looked at goes.
Their testing shows that the rocks on which much of that ice-age-ending theory was based were formed millions of years after the ice age ended, and were formed at temperatures so high there could have been no living creatures associated with them.

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