Images of glaciers breaking apart and dropping into the oceans with magnificent splashes are commonplace on televisions today, threatening the end of arctic life with the impending global warming.
But there is another period of climate change that scientists are concerned with these days - one that is the exact opposite of what is happening today.
Scientists are suggesting that at some point in the past, advancing glaciers conquered the world, creating a "snowball Earth." Glaciers move at incredibly slow rates compared to our short life spans so it is understandable that we don't hear about this theory too often in the news. How riveting can footage of water freezing be anyways?
Did you know? Geologists estimate that an average glacier, hundreds of meters in thickness, would have a top speed of about 2 meters per day, that's roughly 0.000002 km/h.
The threat of glaciers grabbed imaginations in the movie "The Day After Tomorrow" when New York City underwent a sudden ice age. While this movie was perhaps not very accurate in the timeline required to have an ice age (which takes upwards of 50 000 years), it was right in that glaciers have existed in areas which to us would seem very unusual.
Did you know? There is evidence that at one point, the jungles of the tropics were covered in at least a kilometre of ice and snow at the equator.
While there are disagreements among scientists about whether the oceans ever completely froze over, a Snowball Earth would have been covered in 1 km of ice and temperatures at the equator would have resembled those in current day Antarctica. At that time, Snowball Earth would have more closely resembled Mars than today's conditions.
This global freezing was most likely triggered by the break up and separation of an ancient super continent, known as Rodinia, into many smaller landmasses around the equator. This increased the occurrence of a process called 'silicate weathering', which reacts with and sequesters carbon within the oceans. Since carbon dioxide is in equilibrium between the atmosphere and oceans, the amount of CO2 in the atmosphere was gradually depleted to compensate.
Just as the current increase in atmospheric carbon acts as a heavy blanket and raises global temperatures, this reduction of carbon in the atmosphere dramatically dropped global temperatures and resulted in a glacial freeze.
Another compounding effect for global freezing is a concept which also comes up today with global warming and that is the albedo effect.
Did you know? Albedo is the percentage of sunlight which is reflected off the earth's surface.
White surfaces, like snow and ice have a high albedo and they reflect most of the light and warmth which hits them. Dark surfaces, like soil or tree cover, have a low albedo, so just like a black shirt on a hot day, they absorb light and warmth.
Albedo can have a circular effect and played a role in the global freezing since more of the sun's heat was reflected from the increasing snow and ice, making global temperatures even colder.
The opposite of this effect is happening today with the melting of glaciers. As glaciers melt, more earth or open water is exposed, absorbing more heat and therefore raising the global temperature which in turn melts more ice.
It is hard to imagine how that frozen Earth could have returned to the warm and lush planet we live on today but scientists think the reversal was due to volcanoes. Once the planet was frozen, no more weathering occurred. And, due to carbon belching volcanoes, carbon dioxide began to build up in the atmosphere, creating a greenhouse effect which made life today possible.
Wiki on Snowball Earth
Hoffman's research on Snowball Earth