Introduction
In the summer of 1909, an American scientist named Charles Doolittle Walcott (Figure
12.15) was in the Rocky Mountains of British Columbia, Canada. He was a paleontologist,
which is a scientist who studies past life on Earth. He was searching for fossils. Riding on
horseback, he was making his way down a mountain trail when he noticed something on the
ground. He stopped to pick it up. It was a fossil! He began to dig around the area and
found even more fossils. The fossils that Walcott found were of some of the mostbizarre
organisms anyone had ever seen. One of the organisms preserved in the fossils had a soft
body like a worm, five eyes, and a long nose like a vacuum cleaner hose (Figure12.16).
Most of the fossils were the remains of animals that do not live today. They are now extinct,
which means that nothing of their kind lives and that they are gone forever.
Figure 12.15: Charles Doolittle Walcott. ( 21 )The organisms in Walcott’s fossils lived during a time of geologic history known as the
Cambrian. TheCambrianperiodbeganabout540millionyearsago. Itmarkedthebeginning
of the Phanerozoic Eon. It also marked the beginning of many new and complex life forms
appearing on Earth. In fact, the term Phanerozoic means “time of well-displayed life.” We
still live today in the Phanerozoic Eon. However, life on Earth is very different today than
it was 540 million years ago. This lesson covers some of the history of life on Earth. It will
show you how living things have developed and changed over the last 540 million years of
the Phanerozoic Eon. You will learn about how species adapt and evolve over time.