The Earth was once completely covered in Ice. Most likely a meteor impact or mass volcanic activity, or both, was the cause.
The Scientists are pretty sure a large impact at the Antarctic land mass caused massive crust displacement which turned most of Russia into open flowing lava land.
Shock waves collated around the Earth and came together there. Similar to a drip of water in a bucket, when it ripples outward and then back inward and comes together.
When comparing Ice core samples and dating them, there is a distinct link between a colder climate and volcanic activity by measuring the amount of sulfur in the ice.
There is complete documented proof of global cooling in relationship to sulfur and other things in the ice core samples, which is directly connected to volcanic activity of the past by known dates of eruptions.
Including the known super volcano's around the world, and our own Yellowstone.
Which, by the way, is over due according to scientists studying it's history. The average is 600,000 years. They think we are now 640,000 years since it's last major eruption.
In the not too distant past, land has been moving upward in Yellowstone. Tree's and animal deaths are accounted for by mass release of toxic gasses.
By going to google earth, you can see the rough outlines of eruptions of past, and account for tectonic plate movement between eruptions over the Hot Spot.
In the past, tectonic plate movement has been much faster than it is today. When Africa slammed into the European continent, its was estimated to be moving over 2 feet per year.
Today, it is measured accurately by GPS systems and is around 1 cm, or 1/2 inch per year in most cases.
The scientists account for this, in theory, by the cooling of the Earth's core. I personally doubt this tho.
By also going to Google Earth, you can trace the tectonic plate movement over the Hot Spot that has formed the Hawaiian Islands by the mounds on the bottom of the ocean.
There is a new island now forming off the shore of the main island today.
There has been substantial volcanic activity around the world in the past 4 decades.
It's a know fact that the world has gone through several cooling, and thawing periods.
As the Earth is now in a phase of orbit that takes us on a path further from the sun, we are getting warmer. We should be cooling down according to the experts.