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Sand Dollars: Math on the Beach

November 7, 2009 -- From Evelynsaenz, a teacher, from Florida, who is affiliated with the site.

One day at the beach in Costa Rica my daughter and I were digging in the sand making sandcastles when we ran across a live sand dollar. Finding a dead exoskeleton would have been exciting but finding a live sand dollar was unbelievable!

We held it in our hands and felt the tiny hairs on the underside of it’s body tickle our skin ans the animal tried to get away from us and wiggle it’s way back down into the sand. We turned it over and watched it’s mouth moving in the center of it’s flat body.We set it down in the sand and watched it filter sand and water through it’s body and out the five holes that radiate out from the center.

Then we started to feel just under the surface of the sand as the tide washes the waves back and forth and began to find more sand dollars. At first we found one or two. Then we found them by the tens. We soon realized that there were hundreds, thousands and possibly millions of sand dollars right there on that beach.

Talk about a teaching moment!

We spent the rest of the day observing, drawing, measuring and counting sand dollars. This lens is about the math that can be learned at the beach while observing sand dollarsl

Among My Trilobites

March 16, 2007 -- From Frank Galef, a reader, from Oceanside, California, who is affiliated with the site.

I want to tell you about my trilobite website. It is mostly a gallery of my collection along with maps of the Paleozoic that show how the oceans where they lived are related to modern locations. The specimens are arranged by order and family with links to the most comprehensive trilobite site on the Internet (“A Guide to the Orders of Trilobites”). There is no commercial content aside from listing some dealers at the end.

Red Gulch Jurassic Dinosaur Tracksite

March 8, 2007 -- From Rowena, a reader, from Shell, Wyoming, who is affiliated with the site.

At BLM’s Red Gulch Dinosaur Tracksite, you can imagine yourself walking along an ocean shoreline 167 million years ago with dozens of other dinosaurs, looking to pick up a bite of lunch from what washed up on the last high tide. The ground is soft and your feet sink down in the thick ooze, leaving a clear footprint with every step you take.

The discovery of rare fossil footprints on public lands near the Red Gulch/Alkali National Back Country Byway close to Shell, Wyoming, could alter current views about the Sundance Formation and the paleo-environment of the Middle Jurassic Period.