Second Graders Become Archeologists

The second graders are finishing up their study of rocks and minerals by discovering what petrified fossils are. They set up a controlled experiment in which the only variable was the warm salt solution that was added to one of their cups with sand and a sponge bone. The other cup contained all the same materials except plain water was added. The cups dried for several days, and and then the students became archeologists armed with probes, tweezers, and paint brushes. They began to dig out the sponge bones they buried. Many changes had occurred over the week or two time frame. One bone became very hard and filled with a white crystalline material. The other bone remained much the same as the day it was buried. Students began to realize the process of "petrifaction", where living materials are replaced with minerals and harden into rock. The steps they came up with were: quick burial in sand or sediments; change in temperature and moisture; minerals must get into the bone; and TIME! Great job, second graders!