| A | B |
|---|
| homologous structure | similar structures that related species have inherited from common ancestor |
| mold | a hollow space in sediment in the shape of an organism |
| relative dating | a technique used to determine which of 2 fossils is older |
| branching tree | a diagram that showa how scientists think different groups of organisms are related |
| cast | a copy of the shape of the organism that made mold |
| radioactive elements | unable elements that decay or break down |
| radioactive dating | a technique used to determine the actual age of fossils |
| petrified fossils | minerals replace the remains, changing them into rock |
| half time | time it takes for half of the atoms in a sample to decay |
| fossil record | the millions of fossils that scientists have collected |
| extinct | the didsappearance of all members of a species from Earth |
| gradualism | process that evolution occurs slowly but steadily |
| punctuated equilibria | a theory that accounts for the gaps in the fossil record |
| absolute dating | exact date of a fossil |
| sediment | pieces of rock, sand and soil that is carried away by water or wind |
| sedimentary rock | rocks that are cemented together over time |
