Volcanic blasts kicked off modern ice ages
A series of cataclysmic volcanic eruptions gave the planet its polar ice caps, and started a freeze-thaw cycle of ice ages that persists to this day, according to a new theory.
Though we have come to view polar ice as a permanent feature, ice on earth has a checkered past.
Until around 34 million years ago the planet was much warmer than it is today; the Arctic was a vast swamp, Antarctica's mountains were speckled with just a few tiny glaciers. There were no such things as ice caps.
Suddenly, mysteriously, earth's balmy climate cooled. Ice took up residence at the poles, and began marching toward the equator.
Dr Steven Cather of the New Mexico Institute of Mining and Technology and a team of researchers now think they know why.
They argue that a series of massive volcanic eruptions spanning nearly all of present-day Mexico, as well as parts of New Mexico, Arizona, Colorado, and Idaho launched vast amounts of ash into the atmosphere.
"All that stuff in the atmosphere is going to block sunlight," says Cather. "But there's no evidence that it lasts more than a few years, maybe a few decades with a big flare-up. So we thought, what about iron fertilisation?"
As ash rained into the world's oceans, the team's theory goes, it brought in millions of tons of iron that fertilised a feeding frenzy of algae. The photosynthetic creatures harnessed sunlight, nutrients and carbon dioxide (CO2), a potent greenhouse gas, sucking billions of tonnes of it from the atmosphere and chilling the planet.
The team's work was published this week in the journal Geosphere.
But it didn't happen overnight. The Silicic Large Igneous Province erupted as hundreds of explosions between 50 and 15 million years ago.
Each eruption was gargantuan, dwarfing the 1991 Mount Pinatubo blast that briefly cooled global temperatures by 0.5°C.
In all, the team estimates the eruptions launched 400,000 cubic kilometres of ash into the atmosphere during that time, enough material to fill the Caspian Sea five times over, or 710,000 times the volume of Sydney Harbour.
The cumulative effect on climate was immense. Over millions of years, what had been a steamy planet turned into the icy place we know today.
And though the direct effects of the eruptions have faded from view, climate feedback from ice sheets, wind patterns, and changes in the earth orbit are enough to keep us in the glacial cycle deep-freeze ice ages that return every 20,000 to 100,000 years.