click below
click below
Normal Size Small Size show me how
Geologic Time Unit
unit 3 vocabulary
Term | Definition |
---|---|
fossil | the preserved remains or traces of living things |
sedimentary rock | the type of rock made from hardened sediments, where fossils are most commonly found |
mold | a hollow area in sediment in the shape of all or part of an organism |
cast | a solid copy in the shape of an organism, forms when minerals are deposited in a mold |
petrified fossil | fossils in which minerals replace all or part of an organism |
carbon film | an extremely thin coating of carbon on rock |
trace fossil | provides evidence of the activities of ancient organisms (footprints, trails, burrows) |
paleontologist | scientist who studies fossils |
scientific theory | a well tested concept that explains a wide range of observations |
evolution | the gradual change in living things over long periods of time |
extinct | something that no longer exists and never will live on Earth again. |
relative age | the age of a rock compared to the ages of other rocks (tells older or younger) |
absolute age | the number of years since the rock formed |
law of superposition | used to determine the relative ages of sedimentary rocks; in horizontal rock layers, the oldest layer is at the bottom and each layer higher is younger than the one below it |
extrusion | lava that hardens to form rock on the surface of the earth (are younger than the rock layers beneath it) |
intrusion | magma that hardens to form rock beneath Earth's surface (are younger than the rocks around it) |
fault | a break in earth's crust (younger than the rock it cuts through) |
unconformity | a gap in the geologic record made by a younger layer of rock meeting a much older layer beneath it |
index fossil | certain fossils that are widely distributed and represent a type of organism that lived only briefly which helps geologists match and date rock layers. |
atom | tiny particles of matter |
element | matter in which all the atoms are the same |
radioactive decay | certain atoms break down to form atoms of another element releasing particles and energy |
half-life | the amount of time it takes half of and element's radioactive atoms to decay |
geologic time scale | the record of life forms and geologic events in Earth's history |
era | larger divisions of geologic time |
period | subdivisions of eras |
Cenozoic Era | The era we presently live in - referred to as the "age of mammals" |
Mesozoic Era | the "age of reptiles" - dinosaurs were a major life form during this era |
Paleozoic Era | The earliest era of geologic time |