The Cambrian Explosion refers to a time in
Earth’s history, about 541 million years ago, when
lots of new and different animals appeared.
As geologists, we call it an explosion, which you
may think is a very fast event, but it actually
took place over 20 million years! Scientists
are still trying to figure out the reason that all
these new animals appeared, but they have some
ideas. One idea is that oxygen levels increased on
Earth and this let more animals evolve. Another
idea is that the formation of our ozone layer,
which protects us on Earth from harmful rays from
the sun, let more animals live, since conditions
on Earth were not as harsh.
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