Fossils & Geological Time Flashcards
trace fossil
a fossilized mark that is formed in soft sediment by the movement of an animal.
fossil
the remains or physical evidence of an organism preserved by geological processes.
mold
a mark or cavity made in a sedimentary surface by a shell or other body.
cast
a type of fossil that forms when sediments fill in a cavity left by a decomposed organism.
uniformitarianism
a principle that states the geologic processes that occurred in the past can be explained by current geologic processes.
catastrophism
a principle that states that geological change occurs suddenly.
paleontology
the scientific study of fossils
relative dating
any method of determining whether an event or object is older or younger than other events or objects.
superposition
a principle that states that younger rocks lie above older rocks if the layers have not been disturbed.
unconformity
a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.
absolute dating
any method of measuring the age of an event or object in years.
isotope
an atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass).
radioactive decay
the process in which a radioactive isotope tends to break down into a stable isotope of the same element or another element.
geologic time scale
the standard method used to divide the Earth’s long natural history into manageable parts.
eon
the largest division of geological time.
