February 28, 2013
New Details Emerge About ‘Snowball Earth’ Period
Lee Rannals for redOrbit.com — Your Universe Online
About 635 million years ago, our world was covered in ice during an event called "Snowball Earth," and new details written in the Proceedings of the National Academy of Sciences provide new insight on the duration of this event.
According to the Snowball Earth hypothesis, an ice age brought on rapid changes in the atmospheric conditions on our planet, followed by a rapid greenhouse heat wave. This period may have given rise to modern levels of atmospheric oxygen, which helped to pave the way for animals and the diversification of life after.
Researchers set out to find how the planet was able to spring back from the ice apocalypse millions of years ago. Huiming Bao, and Charles L. Jones, Professor in Geology & Geophysics at Louisianna State University (LSU), said the story of our planet is about the incredible resilience of life and life's remarkable ability to restore a new balance between atmosphere, hydrosphere and biosphere after a global glaciation.
"In the study, we concluded that the strange atmospheric O2 isotope event at about 635 million years ago, an event that so far remains singular in the entire Earth history, lasted anywhere from 0 to about 1 million years," Bao told redOrbit.
He said they were able to conclude this in two ways. The first was because they "discovered a sedimentary section that has the largest number of barite layers, so that the duration of the event is best defined in the sedimentary record." Next, Bao said they found "the sedimentary package and carbon isotope curve from this section can be correlated to other sections in the same depositional region where radiometric dates are available."
Barite (BaSO4), a common mineral, was deposited in rocks following the Marinoan glaciation, or Snowball Earth period. The oxygen isotope ratios the team found in barite samples from 635 million years ago could have occurred if Earth's atmosphere had very high levels of carbon dioxide after the Snowball Earth glaciation.
An atmosphere high in carbon dioxide would cause depletion of the O-17 isotope in the air, as well as barite minerals, which use oxygen to grow. O-17 is one of three stable isotopes of oxygen, and the group found deposits of depleted O-17 in sulfate mineral in rocks dating from the global glaciation event during that time period.
LSU graduate student Bryan Killingsworth said their findings show something significant happened in the atmosphere at this time. He said this kind of atmospheric shift in carbon dioxide is not observed during any period of Earth's history.
"This atmospheric event, or MOSD event, reflects pretty much how rapid the Earth system can recover or return to a normal condition after an extreme global glaciation," Bao told redOrbit. "There are questions on how fast atmospheric CO2 had been drawn down and how fast atmospheric O2 had risen by renewed biological activity, or how Earth surface temperature could have varied from superhot to mild after Earth came out of a deep freeze (thanks, probably, to a ultra-high concentration of CO2 in the atmosphere). These questions can only be answered by models that take into consideration of many atmospheric and biogeochemical processes.
"However, without a constraint from the real solid rock record, these models could offer you whatever numbers or scenarios you want. Therefore, our sedimentary constraint on the duration of the MOSD event will provide an very important parameter on any modeling studies on Earth system response at the onset of the great Marinoan glacial meltdown," he added.
He said by using their established approach, future work will be able to refine the exact duration of the MOSD event.
"Finally, as one of our colleagues in the geological age dating business said to me, our work 'puts pressure on the geochronology' because much of the uncertainties in our estimate comes from the minimal half-million-year error in the available radiometric dates," Bao told redOrbit.