| A | B |
|---|
| fossil | preserved remains or traces of living things |
| sedimentary rock | type of rock that is made when parts of rock or the remains of organisms are pressed and cemented together |
| mold | type of fossil formed when an organism buried in sediment dissolves, leaving a hollow area in the shape of the organism |
| cast | type of fossil that is a copy of an organism's shape; formed when minerals seep into a mold |
| petrified fossil | fossil in which minerals replace all or part of an organism |
| carbon film | type of fossil made of an extremely thin coating of carbon on rock |
| trace fossil | type of fossil that provide evidence of the activities of ancient organisms |
| paleontologist | scientist who studirs fossils |
| scientific theory | a well tested concept that explains a wide range of observations |
| evolution | process by which organisms gradually change over long periods of time |
| extinct | type of organism that no longer exists on Earth |
| relative age | the age of a rock compared to the age of other rocks |
| absolute age | the number of years since the rock formed |
| law of superposition | in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger thatn the layer below it |
| extrusion | igneous rock formed when lava flows onto the surface of the Earth and hardens; always yournger than the rock below it |
| intrusion | igneous rock formed when magma hardens beneath the Earth's surface; always younger than the rock surrounding it |
| fault | break or crack in Earth's lithosphere along which the rocks move; always younger than the rock which broke |
| unconformity | place where an old eroded rock surface is in contact with a newer rock layer |
| index fossil | fossils of widely distributed organisms that lived during only one short period |
