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Keenan - Unit 1 - S8

Vocabulary Science 8: Earth History

Geologic Time Scale record of event and organisms that have occurred throughout Earth's history
Fossils are the preserved remains or traces of an organism that lived in the past.
Index fossils A fossil of an organism that lived only during a short part of Earth’s history, many of the fossils must be found in rock layers, it must be found over a wide area of Earth, organism must be unique.
Trace Fossil formed when the mud or sand hardens to stone where a footprint, trail, or burrow of an organism was left behind.
Extinction The permanent disappearance of a species
Law of Superposition The law that states that in any undisturbed sequence of rocks deposited in layers, the youngest layer is on top and the oldest on bottom, each layer being younger than the one beneath it and older than the one above it.
Ice core Core sample from the accumulation of snow and ice over many years
Unconformity A gap in the geologic record
Faults Cracks within the Earth’s rocky crust where rock has been fractured and can move past each other
Plate Tectonics Theory The theory that describes and explains the way the continents separated into today’s land masses from one large landmass.
Sedimentary rocks A type of rock formed when sediment is pressed or cemented together naturally
Radioactive dating method of determining the age of fossils or rocks that is based on the rate of decay of radioisotopes
absolute age The exact age is known due to radioactive dating.
Relative dating Comparing the age of two or more objects
relative age Inferring the age by comparing it with another fossil or rock where the age is known.