Earth & Environmental Science Unit #2

Eon

Longest interval of geologic time

Index fossil

a fossil that is widespread geographically but only occurs in one layer or a small number of layers of rock

Molecular clock

a technique for estimating the age of species by comparing molecular differences between species

Law of Faunal and Floral succession

animals and plant fossils occur in consistent sequences through time, generally changing from simper to more complex

Law of superposition

any undisturbed sequence of layered rocks has the oldest rock on the bottom and newest rock on the top

Radiometric dating

dating a rock or mineral by measuring the proportions of an original radioactive material and its decay products

Uniformitarianism

geologic principle that Earth's processes act in the same manner today as they have always throughout Earth's history

Absolute time

geologic time measured in a specific duration of years

Law of cross-cutting (or intrusive relationships)

in a sequence of layered rocks, the crosscut, or intrusive feature, is younger than the layers it intercedes

Climate

long-term weather patterns of a particular area

Period

major divisions of geologic time with each era; identified by changes in the fossil era

Era

major divisions of geologic time within each eon; identified by major changes in the fossil record

Relative time

placing events in chronological order without reference to their ages measured in years

Rifting

process by which the earth's crust is pulled apart and new crust forms

Law of original horizontality

sediment deposited into water will settle at the bottom in flat, horizontal layers

Law of original lateral continuity

sediment deposited into water will spread in a horizontal and continuous sheet

Paleontology

study of fossils

Stratigraphy

study of rock layers and the processes that form them

Atmosphere

the gaseous envelope of a planet

Mass extinction

the process in which huge numbers of species die out suddenly

Catastrphism

theory that the Earth's rock layers formed in a global flood followed by the uplifting of rocks and mountain building over a short, violent period, possibly in the recent past.