What is an eon?
Q: What is an eon?
A: An eon is the longest period of time in Earth science, lasting hundreds of millions to billions of years.
Q: How is a geologic eon defined?
A: A geologic eon is part of Earth's existence, made up of a number of eras of different lengths.
Q: What is a geologic era made up of?
A: A geologic era is made up of two or more shorter times called geologic periods.
Q: What is a geologic period made up of?
A: A geologic period is made up of yet shorter times called epochs.
Q: How do geologists name eons, eras, periods, and epochs?
A: Geologists give names to all of the eons, eras, periods, and epochs that they have found by looking at rocks.
Q: What do the names given to each eon describe?
A: The names given to each eon describe something about that time, or the rocks that were made at that time.
Q: What is the Phanerozoic eon and when did it start?
A: The Phanerozoic eon is the current eon we live in, which began about 545 million years ago. It is named after the Greek words for life that we can see, referring to the presence of animals and plants big enough to see without a lens.
