Earth's Changing Surface Pt. 3-Geologic Time Flashcards
Fossil
The preserved remains or traces of living things.
Relative Age
The age of a rock compared to the ages of rock layers.
Absolute Age
The age of a rock given as the number of years since the rock formed.
Law of Superposition
The geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it.
Uniformitarianism
The geologic principle that the same geologic processes that operate today, operated in the past to change Earth’s surface.
Intrusion
An Igneous rocky layer formed when magma hardens beneath the earth’s surface; always younger than the rock layers around and beneath it.
Unconformity
A place where old, eroded rock surface is in contact with a newer rock layer; the gap in the geologic record.
Index Fossil
Fossils of widely distributed organisms that lived during only one short period.
Radioactive Decay
The breakdown of a radioactive element, releasing particles and energy.
Half-Life
The time it takes for half of the atoms of a radioactive element to decay.
Carbon-14
A radioactive form of Carbon useful in determining the absolute age of rocks.
Geologic Time Scale
A record of the geologic events and life forms in Earth’s history.
Era
One of the three long units of geologic time between the Precambrian and the present.
Period
One of the units of geologic time into which geologists divide eras.
