June 16, 2011

Researchers Look Into Life After ‘Snowball Earth’

According to MIT researchers, new fossils suggest life had a rapid recovery after a global freeze.

Researchers at MIT, Harvard University and Smith College discovered hundreds of microscopic fossils in rocks dating back about 710 million years, which is around the time frame that the planet emerged from the "Snowball Earth" event.

The team said new fossils are remnants of tiny organisms that survived the harsh post-glacial environment by building armor and reaching out with microscopic "feet" to grab minerals from the environment.

This new discovery is the earliest evidence of shell building in the fossil record.  The team found a diversity of fossils that suggests life may have been recovered relatively quickly following the first major Snowball Earth event.

The Snowball Earth theory says that massive ice sheets covered the planet hundreds of millions of years ago.

Geologists found evidence of two major snowball periods in glacial deposits that formed close to the modern equator.  Fossil records illustrate an explosion of complex, multicellular life following the more recent ice age.

"We know quite well what happened before the first Snowball, but we have no idea what happened in between," Tanja Bosak, assistant professor of geobiology at MIT, and the paper's lead author, said in a statement. "Now we're really starting to realize there's a lot of unexpected life here."

The team went to northern Namibia and Mongolia to obtain samples from cap-carbonate rocks, which are the first layers of sediment deposited after the first ice age.

They discovered tiny dark ovals when looking at the samples under a microscope.  Bosak and colleagues then used scanning electron microscopy to create high resolution, three-dimensional images of the samples.

The fossils from Namibia were mostly round, while those from Mongolia were more tube-like. 

They analyzed the shells' composition using X-ray spectroscopy, finding a rough patchwork of silica, aluminum and potassium particles that the organisms likely plucked from the environment and glued to its surface.

They said these single-celled microbes may have evolved the ability to build shells to protect against the extreme deep-ocean environment.

"We can now say there really were these robust organisms immediately after the first glaciation," Bosak said in a statement. "Having opened this kind of window, we're finding all kinds of organisms related to modern organisms."

The closest modern relative to this fossil may be testate amoebae, a single-celled microbe found in forests, lakes and peat bogs. 

Bosak said that testate amoebae were extremely abundant before the first Snowball Earth.

She said the team plans to return to Mongolia to sample more rocks from the same time period.

Andrew Knoll, the Fisher Professor of Natural History and professor of earth and planetary sciences at Harvard, said the group's discovery points to a potentially rich source of information about the kinds of life between glacial periods.

"To date, we've known very little about life between the two large ice ages," Knoll said in a statement. "With this in mind, the new discoveries are truly welcome."

The team published their findings in an upcoming issue of Earth and Planetary Science Letters.


Image Caption: Scanning electron microscopy images reveal a microscopic, oval-shaped shell with tapered ends, from which an organism's feet may have extended. The surface of the shell is made up of tiny bits of silica, aluminum and potassium, which the organism likely collected from the environment and glued to form armor. Image: Tanja Bosak


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