SNOWBALL EARTH
750 to 600 million years ago. The worlds land and oceans frozen over. Ice sheets kilometres thick. It sounds like the setting of a disaster movie, yet this isn’t fiction, it is an ancient ice age, “Snowball Earth”.
What was Snowball Earth?
Snowball Earth describes a period of the planets history where the worlds oceans and land was repeatedly frozen over in kilometres of ice. At the equator the temperature fell to arctic levels, suggesting the rest of the world was much colder.
This global ice age lasted from around 750 to 600 million years ago and put the development of life on hold and under threat.
Where is the evidence?
The theory of the mega ice age was put forward by Joseph Kirschvink in the 1990’s. Kirschvink had noted glacial deposits in tropical latitudes, such as north west Canada. Canada might not seem tropical, but 700 million years ago Canada would have laid right along the equator, the most tropical place on earth. These glacial deposits were ancient and could’ve only been moved from the poles to the equator all that time ago but a natural force, not air, not water, but ice.
It was realised that if ice could survive at the equator, it could easily survive everywhere else on the Earth. The conclusion was our planet encased in ice.
What caused it?
Ice ages are often caused by a reduction in greenhouse gases, such as Carbon Dioxide and Methane, Snowball Earth was no exception. With fewer of these gases, the climate grows colder, known as global cooling. This cooling would lead to ice forming, ice is an excellent reflector of light and when the sun shone onto these ice sheets it reflected straight back off. It was worked out that if approximately half the Earth became covered in ice, it would create a runaway effect, the ice would reflect so much light it would rapidly spread to the equator.
How did it end?
Although land masses were buried under a few kilometres of ice, plate tectonics continued uninterrupted, as a result so did volcanic activity. Greenhouse gases were buried under huge amounts of ice and during an estimated 5 to 30 million years, volcanic activity managed to release enough Carbon Dioxide and Methane to create an ice-free belt around the equator. This belt then absorbed heat from the sun and triggered the end of Snowball Earth.
Did life survive?
During Snowball Earth complex life had not evolved, only microbial lifeforms and stromatolites survived through the ice. It’s thought live could’ve survived in anaerobic conditions or near hydrothermal vents deep below the surface, or even as eggs in dormant cells and spores.
