appeared on this planet some 3.8 billion years ago, but consisted
entirely of microbes until the Cambrian explosion just 600 million
years ago- practically yesterday on the geologic time scale.
What triggered this huge and rapid leap from single- to multicellular
scientists believe our planet was once completely encased
In “Noah’s Snowball,” Drs. Paul
Hoffman and Daniel Schrag
of Harvard present what they call the “Snowball Earth” hypothesis.
Based on geologic evidence from Namibia, China and New England,
Hoffman and Schrag propose that 600 million years ago, the Earth
cooled a few degrees, setting off a feedback loop that left
the entire planet entombed in ice miles thick. The Earth's volcanoes,
however, reversed the trend by belching carbon dioxide, the
now notorious greenhouse gas, into the atmosphere. Within a
hundred years, Hoffman and Schrag hypothesize, the planet's
climate flip-flopped from the coldest it's ever been to the
points to ancient evidence of Earth's biggest climate
this rapid reversal have spurred on animal evolution, resulting
in the parade of life that ranges from plankton to people?
Scientific American Frontiers travels from Boston to Yellowstone
National Park to China to pinpoint the origin of animals.
more on this topic, see the web feature: