Term | Definition |
relative dating | estimate of the age of a fossil based on the location of the fossil in strata |
radiometric dating | technique that uses the natural decay rate of isotopes to calculate the age of material |
isotope | form of an element that has the same number of protons but a different number of neutrons as another element |
half-life | amount of time it takes for half of the isotope in a sample to decay into its product isotope |
index fossil | fossil of an organism that existed during only specific spans of geologic time across large geographic areas |
geologic time scale | time scale representing the history of Earth |
era | second largest unit of geologic time, lasting tens to hundreds of millions of years and consisting of two or more periods |
period | unit of geologic time that lasts tens of millions of years and is associated with a particular type of rock system |
epoch | smallest unit of geologic time, lasting several million years |
nebula | rotating cloud of gas and dust |
ribozyme | RNA molecule that can catalyze specific chemical reactions |
cyanobacteria | bacteria that can carry out photosynthesis |
endosymbiosis | ecological relationship in which one organism lives within the body of another |
Paleozoic | era of geologic time (from 544-248 million years ago) during which members of every major animal group alive today evolved |
Cambrian explosion | earliest part of the Paleozoic era, when a huge diversity of animal species evolved |
Mesozoic | era during which dinosaurs roamed Earth (from 248 million years-65 million years ago) |
Cenozoic | geologic time period that began 65 million years ago and continues today |
primate | mammal with flexible hands and feet, forward-looking eyes, and enlarged brains relative to body size |
prosimian | oldest primate group that includes mostly small, nocturnal primates such as lemurs |
anthropoid | humanlike primate |
hominid | primate group that includes orangutans, chimpanzees, gorillas, and humans, as well as their immediate ancestors |
bipedal | animal that walks on two legs |