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.
