7th Period 8th Grade Science Geologic Time Test Review

Fossils

are the preserved remains or traces of living things; they provided evidence of how life has

changed over time

paleontologist

scientist that studies, collects & classifies fossils

fossil record

all the information that paleontologists have collected about past life

evolution

the gradual change in living things over long periods of time

extinct

an organism no longer exists & will never again live on Earth

The Relative Age of Rocks

the rock's age compared with the ages of other rocks

absolute age

the number of years since a rock formed

index fossils

a fossil that is widely distributed & represents a type of organism that existed only briefly

Law of superposition

in horizontal sedimentary rock layers the oldest layer is at the bottom

cross-cutting relationships

study extrusions & intrusions of igneous rock

study of faults

a fault is always younger than the rocks it cuts through

study of unconformity

a gap in the geologic record that shows where some rock layers have been lost because of erosion

Radioactive Dating of Rocks

the process of using radioactive rocks to determine the numerical age of a rock

Planetary Differentiation

where a planetary body develops into compositionally distinct layers, the denser materials sink to the center, while the less dense materials rise tot he surface

Geologic Time Scale

a record of the life forms and geologic events in Earth's history, it is used to show Earth's history

Molds and Casts

most common fossils; are a hollow area in sediment in the shape of an

organism or part of it; forms when dissolved minerals in water seep into the empty space of a hollow area in sediment in the shape of the organism

Petrified Fossils

minerals replace all or part of an organism

Carbon Films

an extremely thin coating of carbon on rock

Trace Fossils

these provide evidence of the activities of ancient organisms

Preserved Fossils

Tar, Amber, & Ice

Law of Original Horizontality

rocks & sediment are always deposited in horizontal layer

half-life

the amount of time that it takes for 1/2 of a portion of radioactive material to break down into a new stable element

Eon

88% of Earth's history; ended 544 million yrs. ago

Era

the three largest divisions of geologic time after the Precambrian.

Period

subdivisions of each of the 3 Eras - are named after places in the world where geologists first discovered the rocks and fossils of each period