Cambrian Period, the first geologic period of the Paleozoic Era. It began 570,000,000 years ago and lasted 70,000,000 years. It is named for Wales (which the Romans called Cambria), where sedimentary rocks of the period were first recognized.
One grows from the ground and one from the ceiling, but sometime's it's hard to remember which is the stalactite and which is the stalagmite. How do they get there, anyway?
When it comes to fossils, specimens like Sue the Tyrannosaurus rex grab much of the attention. And while Sue is a staggering 67 million years old, she's a new kid on the block, compared to some of the oldest fossils ever found. What's older than Sue?