A technique that uses the natural decay rate of unstable

isotopes found in materials in order to calculate the age of that material.

Are atoms of an element that have the same number of protons but a different number of neutrons.

An era, which began 542 million years ago

Animlas that walk in two legs call

This era are divided into three periods: the Triassic, the

Jurassic, and the Cretaceous.

The earliest member of the genus Homo was

Are the oldest living primate group, and most are small and active at night.

During this period, placental mammals and monotremes—a small group of mammals that lay eggs—evolved and diversified

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