| A | B |
|---|
| absolute age | the actual age of a rock or fossil or how long ago an event occurred |
| adaptation | a trait or structure that improves an organism's chance for survival |
| asthenosphere | the soft layer of the mantle made up of semisolid rock that flows slowly |
| Cambrian boundary | the point at which variety of life on Earth exploded about 550 million years ago |
| chemical weathering | a process that changes the chemical composition of rocks |
| continental drift | the process by which the continents split apart from a single landmass |
| contour line | a line on a topographic map that connects areas with the same elevation |
| convergent boundary | the location where two tectonic plates push together |
| divergent boundary | the location where two tectonic plates pull apart |
| earthquake | the shaking of Earth's surface that occurs when energy stored as pressure in rocks is released quickly |
| evolution | the process of change over time |
| extinction | the disappearence of species from Earth's surface |
| fault | a break or crack in Earth's surface along which movement occurs |
| fossils | imprints or remains of organisms that were once alive |
| geologic time scale | the timeline that organizes the events in Earth's history |
| hot spot | an area of volcanic activity in the middle of a tectonic plates |
| index fossil | the fossil of an organism that existed for a relatively short period of time |
| K/T layer | the rock layer formed between the Cretaceous and Tertiary periods; marks the extinction of the dinosaurs |
| lava | magma that reaches Earth's surface |
| law of superposition | a scientific law that states that in an undisturbed sedimentary rock layers, older layers of rock lie beneath younger rock layers |
| lithosphere | the uppermost layer of Earth, made up of crust and mantle |
| mass extinction | the disappearence of a large number of species in a fairly short period of time |
| mechanical weathering | the process that breaks rocks apart without changing their chemical composition |
| natural selection | the theory that explains how populations can eventually evolve into new species |
| plate tectonics | the theory stating that the lithosphere is broken into giant chunks of land or ocean floor that can slowly move |
| radioactive dating | the means of measuring the age of a material by comparing the amount of a radioactive form of an element of its decay product |
| subduction | the process in which one tectonic plate is pushed under another |
| tectonic plates | giant chunks of land or ocean floor |
| theory of plate tectonics | a theory that states that Earth's lithosphere, or land, is broken into large sections called tectonic plates that move and change position over time |
| topographic map | the means of visually showing the features of a region using colors, lines and special symbols |
| topography | the study of Earth's natural and artifical features by surveying and mapping |
| transform boundary | the location where two tectonic plates slide past each other |
| unconformity | a gap in the rock record |
| volcano | an opening in the Earth through which magma is released |
| weathering | process in which rocks are broken down into smaller pieces though the action of wind, water, roots, and animals |
