12 Questions
When did life start on Earth according to the geologic time scale?
3.5 billion years ago
What were the main life-forms during most of Earth's early history?
Algae and bacteria
When did complex organisms such as land plants and fish appear?
Within the last 500 million years
When did humans first appear on Earth?
About 200,000 years ago
How long ago did the Phanerozoic eon begin?
About 550 million years ago
What is a mass extinction?
The permanent dying out of a species or a larger group of organisms
What is a mass extinction?
The sudden disappearance of many fossil species followed by the sudden appearance of new species.
What is a catastrophe in the context of Earth's history?
A sudden, severe change in conditions on Earth.
What event could potentially cause a mass extinction?
An asteroid or comet crashing into Earth.
What are the divisions of geologic time after the Proterozoic Eon?
The Phanerozoic Eon, divided into three eras: Paleozoic, Mesozoic, and Cenozoic.
What marks the beginning of the Cambrian period?
The Cambrian explosion.
Which era has the most fossils found by paleontologists?
Cenozoic era.
Learn about the geologic time scale, a timeline organizing major events in Earth's history from its formation to the present. Explore how life evolved over billions of years, starting with simple organisms in the oceans around 3.5 billion years ago.
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