| Question | Answer |
| fossils | the preserved remains or traces of organisms that lived in the past
|
petrified fossil2 | a fossil formed when minerals replace all or part of an organism2
| extinct3 | A type of organism that no longer exists on Earth is said to be _____________3
| relative age4 | age compared with the ages of other rocks4
| Intrusion5 | _____________ igneous rock is always younger in relation to the sedimentary rock layers which it passes5
| half-life6 | The time it takes for half of the radioactive atoms in a sample of a radioactive element to decay is the element's _________6
| radioactive decay7 | occurs when atoms of some elements break down to form atoms of another element7
| absolute age6 | Geologists use radioactive dating to determine the _________ of rock8
| uniformitarianiam9 | What principle states that the geologic processes that change Earth today also changed Earth in the past?9
| trace fossils10 | Footprints and trails are examples of _____________________10
| geologic time scale | Geologists divide Earth's long history into smaller units that make up the _________
| carbon film | Plant leaves may form a fossil called a __________, a thin layer of carbon on rock.
| unconformity | A gap in the geologic record where some rock layers have been lost because of erosion is _____________
| Index | _________ fossils are helpful to geologists because they reveal the relative ages of the rock layers in which they occur.
| Paleontologists | scientists who study fossils
| mold | a hollow area in sediment in the shape of an organism or part of an organism
| cast | a solid copy of the shape of an organism
| evolution | the change in living things over time
| law of superposition | According to the ________________, in undisturbed horizontal sedimentary rock layers the oldest is at the bottom. Each higher layer is younger than the layers below it.
| extrusion | Lava that hardens on the surface and forms igneous rock
| fault | a break in Earth's crust
| era | One of the three long units of geological time between the Precambrian and the present
| period | One of the units of geologic time into which geologists divide eras |
