| A | B |
|---|
| fossil | a trace of an ancient organism that has been preserved in rock |
| sedimentary rock | a type of rock that forms when particles from other rocks or the remains of plants and animals are pressed and cemented together |
| mold | a fossil formed when an organism buried in sediment dissolves, leaving a hollow area |
| cast | a fossil that is a copy of an organism's shape, formed when minerals seep into a mold |
| petrified fossil | a fossil in which minerals replace all or part of an organism |
| carbon film | a type of fossil consisting of an extremely thin coating of carbon on rock |
| trace fossil | a type of fossil that provides evidence of the activities of ancient organisms |
| paleontologist | scientist who studies fossils |
| scientific theory | a well-tested concept that explains a wide range of observations |
| evolution | the process by which all the different kinds of living things have changed over time |
| extinct | a type of organism that no longer exists anywhere on Earth |
| relative age | the age of a rock compared to the ages of other rock layers |
| absolute age | the age of a rock given as the number of years since the rock formed |
| law of superposition | states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it |
| extrusion | an igneous rock layer formed when lava flows onto Earth's surface and hardens |
| intrusion | an igneous rock layer formed when magma hardens beneath Earth's surface |
| fault | a break or crack in Earth's surface |
| unconformity | a place where an old, eroded rock surface in contact with a newer rock layer |
| index fossil | fossils of widely distributed organisms that lived during only one short period |
