This is a picture of the Silver Peak Mountain Range in the Nevada desert. It is the home of cacti, lizards, rattlesnakes and other desert dwellers.

However, the rocks of this slope contain fossils of animals quite different from those found there today.

There are fossils of marine animals, like this archaeocyathid, in the rocks of this desert.

Archaeocyathids were a group of sponges that lived about 500 million years ago, and are now extinct.

They built huge reefs (similar to coral reefs we see today) and were extremely important members of their ecosystems.

What could explain finding fossils of sponges in the Nevada desert?

a) Sponges used to live in the desert.
b) Nevada used to be covered by water.

And archaeocyathids are not the only fossils of marine animals found in this desert. There are lots of them.

These fossils tell us that there used to be an ocean in Nevada where there is now a desert!

Archaeocyathids are very similar to marine sponges. Since we know that today’s sponges cannot live outside of salt water, it is very unlikely that archaeocyaths could live in the desert! Try again...