Podcast
Questions and Answers
The geologic time scale is a timeline that organizes major events in Earth's ______.
The geologic time scale is a timeline that organizes major events in Earth's ______.
history
For more than a billion years, there were no life-forms on our planet, until life started in the oceans around 3.5 billion years ago with simple organisms such as algae and ______.
For more than a billion years, there were no life-forms on our planet, until life started in the oceans around 3.5 billion years ago with simple organisms such as algae and ______.
bacteria
Complex organisms such as land plants and fish appeared only within the last 500 million ______.
Complex organisms such as land plants and fish appeared only within the last 500 million ______.
years
Humans did not appear until about ______ years ago.
Humans did not appear until about ______ years ago.
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Almost all known fossils come from the most recent eon, the ______.
Almost all known fossils come from the most recent eon, the ______.
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Mass extinctions have occurred many times in Earth's ______.
Mass extinctions have occurred many times in Earth's ______.
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A sudden, severe change in conditions on Earth is called a ______.
A sudden, severe change in conditions on Earth is called a ______.
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One event that could cause a mass extinction is an asteroid or comet crashing into ______.
One event that could cause a mass extinction is an asteroid or comet crashing into ______.
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Periods are divided into ______, which are the shortest divisions of geologic time.
Periods are divided into ______, which are the shortest divisions of geologic time.
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The last eon of the Precambrian is the ______ Eon.
The last eon of the Precambrian is the ______ Eon.
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Geologic time after the Proterozoic Eon is called the ______ Eon.
Geologic time after the Proterozoic Eon is called the ______ Eon.
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The beginning of the Cambrian is marked by the Cambrian ______, named because of the great variety of living things that developed during that time.
The beginning of the Cambrian is marked by the Cambrian ______, named because of the great variety of living things that developed during that time.
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