Snowball Earth

The "Snowball Earth" hypothesis is an idea that after billions of years of

existing, Earth suddenly fell into a winter so extreme that it makes recent ice

ages look warm.(New Scientist 2005) Then the ice melted again, and the planet sweltered in a climatic change of intense heat which basically "baked" earth. Between 750 million and 590 million years ago, supporters of the "Snowball Earth" hypothesis say, the climate may have went back and forth between deep freeze and heat as many as four times. The entire earth may have been covered in ice as much as one kilometer thick. The temperature hovered around negative forty degrees Celsius.(Walker 2004)

Answering questions about Earth's climate of more than half a billion years ago can be a challenge, even questions as bare as whether land and sea were completely layered by ice from pole to pole. Indeed, the revival of the Snowball Earth hypothesis almost 7 years ago has slowed down of late, as paleoclimatologists have failed to turn up clear evidence that ice covered our planet.(Anderson 2005) For many years geologists have been assembling data signifying that Earth has gone into a deep freeze on numerous occasions, with ice layering even the equator and with potentially destructive costs for life. The theory, known as "Snowball Earth," has been deficient of a decent justification for what triggered the global glaciations.(Walker 2004) Now, the California Institute of Technology research group that began the Snowball Earth theory has projected that the reason for the earliest and most serious incident may have been an organism as low as bacteria that, by releasing oxygen, destroyed a crucial gas that kept the planet warm.(Narbonne 2003)

Another theory is that the Milky Way is laced with huge clouds of hydrogen, which are concentrated largely in the galaxy's spiral arms. As our solar system orbits the center of the galaxy it passes in and out of these arms, coming across about eight such clouds in the 250 million years that it takes to accomplish an orbit.(Reich 2005) The damage would be done by the sprinkling of carbon and silicate dust particles these clouds contain. The Earth's atmosphere is normally protected from this dust by the pressure of the solar wind, a blast of hot ions streaming out from the sun. But around 1 in 30 of these gas clouds are dense enough to overpower the solar wind, allowing dust to pour into the Earth's atmosphere.(Walker 2004) The influx would block as much sunlight as the outpourings from three volcanic eruptions a year, and it would last a lot longer. The result of this would be the Snowball Earth. While Earth will hardly ever come across galactic clouds thick enough to set off a global ice age, less dense clouds could also have a serious effect. By compressing the protective solar wind shell surrounding the solar system, they might allow galactic cosmic rays and hydrogen from the cloud to enter the atmosphere. This would destroy the Earth's ozone layer and allow in ultraviolet-B radiation from the sun that would kill off many species.

Scientists across the world are beginning to believe that in the past the Earth froze over completely for ten million years, but then warmed up rapidly about 600 million years ago. Almost all life was wiped out. But out of the freeze emerged the first complex creatures on Earth.(Walker 2004)

The 2 main ideas are the "Snowball" hypothesis and the "Slush ball" hypothesis. The two sides disagree over the severity of the glaciations that occurred during the freeze.(Walker 2004) The "Snowball" supporters say that the glaciations were widespread and covered nearly the whole Earth. Many signs of past glaciations have been found in places that should have been much too hot for example very near the equator. They believe that glaciations were finally broken by a greenhouse effect that melted the glaciers. The Snowball Earth theory has sparked controversy among geologists, many of whom shy away at the notion of a world fully covered in ice.(Reich 2005) While many scientists are still trying to figure out about exactly how far the ice went, almost everyone now agrees that this was a time of unusual, exceptional cold. During the more recent ice ages of mammoth and mastodon fame, ice barely reached as far south as New York.(Narbonne 2003) So if the earth was completely covered in ice, this shows exactly how much more severe this ice age was compared to the most recent ones.

The first question facing palaeontologists willing to test the Snowball idea is when exactly did multicellular life come about? Until recently, it seemed that this significant event occurred during the Cambrian explosion , a period of speedy progression of new evolutionary shapes and strategies, during which