What does a marine fossil in the desert tell scientists? a: marine life once lived on a land b: the desert was always a desert c: the area was once under water d: marine fossils cannot be found in a desert

The correct answer is C.

There are examples of desserts that were once seas and oceans.The Tethys sea that once covered the Sahara desert retreated.  Because the earth has tectonic plates that are constantly moving and shifting, places that were once oceans may be raised up high above sea level causing the sea to retreat. Marine life that once lived in the ocean and died will remain there and may be uncovered as time goes on.  For this reason, if marine fossils are found in the desert it means that at some point in history, that area was once under water.