dioxide belched from ancient volcanos helped to rewarm
the abundance of geologic evidence, scientists remained skeptical
of the Snowball Earth hypothesis. How could the snowball ever
have melted, they wondered. Modern climate modeling provided
an answer. The processes that normally remove carbon dioxide
from the atmosphere, such as rain and photosynthesis, would
have been suspended during the Snowball years. The gas would
have simply built up until the notorious "greenhouse effect"
kicked in, trapping energy from the sun and warming the planet.
Namibian sediments support the idea that the Earth warmed
up just a quickly as it cooled. Hundreds of meters of limestone
sit directly on top of the glacial deposits. Since limestone
forms only in warm water, the juxtaposition of these two sediments
implies a global temperature swing from icy to tropical in
a very short period of time- probably a few years, according
all Hell broke loose," says Schrag. "The global temperature
would have averaged higher than 90 degrees Fahrenheit. Today,
it's in the 50's."
banded iron formation provides evidence of warm temperature
immediately following glaciation
formations in the glacial deposits provide still more evidence
of this rapid climatic shift. The tropical glacial deposits
contain thick layers of iron, called banded iron formations,
which only occur when extremely iron-rich seawater is suddenly
exposed to oxygen. Normally, atmospheric oxygen prevents iron
from building up in the world's oceans. But Hoffman and Schrag
suspect that sheets of ice insulated the ocean from the atmosphere
for millions of years, allowing iron levels to skyrocket.
The banded iron formations found in the glacial deposits mark
the geologic moment when the ice melted and the sea met the
- - - - - - - - - -
pages: | 1 | 2 | 3