Answer:
About 540 to 490 million years ago
Explanation:
The Cambrian is the first and oldest division of the Paleozoic era on the geologic time scale. The other periods in the Paleozoic are the ordovician, silurian, devonian, carboniferous and permian. At the permian a mass extinction occured.
The cambrian is marked with the evolution of lot of life and it is typified by the presence and dominance of trilobites.
