You might not have guessed it, but among paleontologists who study fossil reefs, Nevada is quite famous. The earliest reefs on Earth, those of the Cambrian Period, were not constructed by corals. Corals had not yet evolved. These pioneer reefs were built by a consortium of calcareous sponges (called archaeocyaths) and algae. Archaeocyathan reefs first appeared about 530 million years ago in the Cambrian Period, in equatorial latitudes, on the outer edges of continents.
Nevada was on the margin of North America in the Cambrian Period, lying close to the equator, so it was perfectly situated for reef development. Most of California did not yet exist. Rock exposures in Esmeralda County, in southwestern Nevada, contain some of the best preserved and well-studied archaeocyathan reefs on Earth.
(1) The first image shows an exposure of one of the most famous ones, near the semi-ghost town of Gold Point. This reef has been visited by hundreds of geologists and geology students from around the world.
(2) The second image is a close-up view of branching archaeocyathan sponges within this reef. The scale in the photo is 10 centimeters (4 inches) long. The branching archaeocyath in the photo was probably ripped up and knocked over by a wave, but it recovered by sending up a new vertical branch. These sponges stabilized the sediment and allowed the reef to build up to sea level.
Visit the Prehistoric Life Gallery of the Las Vegas Natural History Museum to see a beautiful mural depicting archaeocyathan reefs, together with some of the marine animals that co-existed with them. -Dr. Rowland