Life forms in the Precambrian include

Radiometric dating is based on

When precipitation at the ocean surface exceeds evaporation, the salinity of seawater

Coastal lands bordering the oceans generally have

Almost all of Earth’s supply of energy comes from

Solar radiation consists of waves principally in the

The most important event during the Cambrian period was the

In the tropics, the trade winds drive equatorial ocean currents

Conditions for the preservation of fossils are best achieved

Earth’s first atmosphere was composed of