The time from the formation of Earth 4.6 billion years ago to about 543 million years ago. Life on Earth began during this time

Organisms that contain a nucleus and other complex structures in their cells. These organisms appeared about 1 billion years ago

A gas in the atmosphere which absorbs harmful radiation from the sun

The most recent geologic era, beginning 65 million years ago; also called the Age of Mammals

What are the four biggest eras in geologic history?

How many cells did the first living things, prokaryotes, have?

living things that first made food from sunlight

gas that cyanobacteria sent into oceans and air

a layer of gas around the earth that keeps out radiation

A billion years after Earth formed, what kind of living things appeared?

What happened to almost all living things from the Paleozoic era?

What are the best-known reptiles of the Mesozoic era?

Unlike the atmosphere today, the atmosphere 3.5 billion years ago did not contain

Before an ozone layer formed and reduced the radiation reaching the Earth’s surface, most life existed

Fossils indicate that some of the first animals to live on land were

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