Earth's History: Freeze and Fry

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Snowball Earth

According to Paul Hoffman from Harvard, some 700 million years ago all the planet’s landmasses formed a single continent – Rodinia - straddling the Equator. The polar seas began to freeze. Their brilliant white surface reflected sunlight, cooling the planet until the entire Earth froze over. Rather like Jupiter’s moon Europa today (pictured), our planet was a cosmic snowball. Life could only survive at hot volcanic vents on the ocean floor.

Hoffman believes that volcanoes eventually pumped enough carbon dioxide and other greenhouse gases into the atmosphere, to heat the Earth until the ice began to thaw. As more of the dark ocean surface was exposed, it absorbed more of the Sun heat: the seas became warmer and the ice rapidly melted.

Hammer from the Heavens

Mike Baillie, of Queen’s University, Belfast, has been checking out wood from ancient forts in Northern Ireland. Within the tree-rings of the ancient oak logs, he’s found one band where the rings are very narrow – a few years when the tree struggled hard to survive. Baillie dates it to AD 536.

That had to be a period when the climate was extremely bad. Indeed, chroniclers from around the world – from Italy to China – complained about the bad weather and consequent famine. Baillie links it to the appalling conditions that were supposed to follow the death at that time of Britain’s warrior hero, King Arthur.

Baillie blames the appalling conditions on a comet (like Hale-Bopp, pictured below) that impacted the Earth, and spread cooling dust around our planet – a bigger cousin of a comet or asteroid that was seen to explode over Siberia in 1908.

That’s not the only danger we face from the sky. Jan Veizer of the University of Ottawa has been looking inside meteorites, to see how the Solar System – including the Earth – is affected by cosmic radiation, as the Sun moves around the Milky Way Galaxy. He has found the radiation peaks every 143 million years – matching the changing temperature of the Earth. Veizer proposes that the cosmic rays would seed clouds on Earth, so reducing the planet’s temperature. He claims that – through the geological past – cosmic rays have been twice as effective as carbon dioxide in controlling Earth’s temperature.

Whatever effects the Cosmos has on us, it’s something we have no hope of controlling – and not even of predicting. As the dinosaurs found out 65 million years ago, if you’re unlucky enough to be in the path of a runaway asteroid, then the climate is going to be unimaginably extreme. When that asteroid hit the Earth, it created a fireball at over a thousand degrees that literally roasted the dinosaurs alive.

That was the ultimate “fry” in the Earth’s long history, just as Snowball Earth was the ultimate “freeze”. These geological perspectives prove that our current global warming is a mere blip as compared to the changes that nature can inflict on our planet.

But that’s no reason for us to be complacent. Though our planet has survived these extreme climate swings, and life has somehow pulled through, the Earth’s cycles of freeze and fry have always destroyed the dominant species of their time…

For more information

US Environmental Protection Agency on causes of past climate change
http://www.epa.gov/climatechange/science/pastcc.html

Christopher Scotese on changing climate throughout Earth's history
http://www.scotese.com/climate.htm