Wednesday, December 9, 2009

Cosmic crash in Canada boosted life

Did life begin in Sudbury?
Vancouver Sun: The mountain-sized meteorite that struck Sudbury nearly two billion years ago -- already known to have made the northern Ontario city a global mining mecca -- may have also triggered changes in Earth's ocean chemistry that allowed complex life to begin evolving on the planet...

Scientists John Slack and Bill Cannon of the US Geological Survey say the colossal Canadian impact 1.85 billion years ago may have generated an unprecedented 'mega-tsunami' that stirred oxygen into the deep ocean and jump-started the evolution of organisms beyond their bacterial beginnings.

Prior to the massive collision, which scientists have compared to an object the size of Mount Everest striking primeval Canada, anaerobic bacteria living in the depths of the ocean left their traces in distinctive iron formations that can be seen at various sites around Lake Superior...

Then, following the cosmic crash that left a 200-kilometre wide crater in the area around Sudbury, the layer of 'banded' iron formations abruptly stops and is covered by a strata of 'ejecta' -- shocked fragments of rock blasted hundreds of kilometres from the epicentre of the meteorite strike.

A number of Canadian and American scientists have been documenting these Sudbury ejecta sites over the past decade, gradually producing a clearer picture of an event now believed to rival in scale the Mexican impact 65 million years ago that's associated with the demise of the dinosaurs.

But in a 'speculative' paper published in the November issue of the journal Geology, Slack and Cannon suggest the Sudbury meteor strike was so enormous that the super-tsunami and shock waves that fractured parts of the Earth's crust far and wide combined to permanently alter the oxygen makeup of the planet's oceans.

Other scientists, Slack told Canwest News Service, 'have invoked gradual processes in Earth's history' to explain the sudden halt to the bacteria-assisted iron formations about 1.85 billion years ago. 'We're suggesting it was a catastrophic cause' linked to the Sudbury meteorite strike.

The mixing of the oxygenated upper surface of the ocean with oxygen-starved deeper waters may have doomed iron-loving bacteria and created a 'niche' for other microorganisms better suited to a marine environment evolving to favour oxygen-dependent life forms.
Image source here.