Okay, we know that when tectonic plates collide, they can push up huge mountains. We know this because it's still happening in the Himalayas. Hundreds of millions of years ago, this happened on an even bigger scale, producing enormous "supermountain" ranges. The way they figured this out is pretty neat, involving the radioactive decay of the uranium contained in zircon. This happened somewhere around 650 million years ago, before there was life on land. These mountains eventually eroded away over a long time, which coincided with the Cambrian Explosion, and may have even sparked it.
This theory came about as scientists worked backwards to explain the effects. Now, in science, we want experiments to be replicable, and that's not really possible in geology. But as complicated as the story is, they found that this wasn't the first time it happened in earth's history. And that's what replication is in geology. -via Damn Interesting
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