Now, with 90 percent of Earth history behind us, it's time for conquest. The tremendous explosion of life that began in the oceans of the Cambrian was still going strong at the dawn of the Ordovician, the second of the six great periods that make up the Paleozoic. And it was in Ordovician oceans that a second wave of animal experimentation began, as well, one that ultimately would lead to the first Australians coming ashore. With the seas now crowded with life, the first tentative footsteps onto land were not far away. Now, at the time, Australia was just one of an exotic collection of lands, including India, Africa, South America and Antarctica, that, today, we call the supercontinent
