26 terms

Chapter 21: Fossils & Geologic Time

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Geologic Time Scale
A record of Earth's history from its origin 4.6 billion years ago to the present
Intrusion
When igneous rock is formed through existing rock formations. Formed when hot magma seeps into cracks of existing rocks and cools.
Uniformitarianism
States that the processes that are happening on Earth today have been occurring since Earth first formed
Law of Superposition
States that the oldest layers of rock are found at the bottom and the youngest layers of rock are found at the top if the layers have not been disturbed.
Fossil
Remains or evidence of a once-living plant or animal
Index Fossil
Remains of plants or animals that can be used to determine the age of a rock layer, or to match rock layers over a large geographic area
Extinction
The disappearance of all members of a species from Earth
Mass Extinction
An event during which MANY SPECIES become extinct during a relatively short period of time
Absolute Dating
A technique used to determine the actual age of a fossil in YEARS
Relative Dating
A technique used to determine whether a rock/event is older or younger than other rocks/events
Radioactive Decay
Process in which radioactive elements break down and turn into new elements. Used to determine the age of rocks.
Half-Life
Length of time required for half of the radioactive atoms in a sample to decay
Eon
The longest unit of time & it is measured in billions of years
Era
The second longest unit of time & it is measured in hundreds of millions to billions of years
Period
Determined by the life-forms that were present or became extinct during the time when specific rocks were deposited (usually measured in tens or hundreds of million years)
Epoch
One of the smaller divisions of time & it is measured in millions or tens of millions of years
Unconformity
A gap in the rock record that is caused by erosion or weathering
Mold
Formed when the original shell parts of an organism within a sedimentary rock are weathered and eroded leaving a hollowed-out imprint of the shell
Cast
When a mold is filled with minerals or sediment that harden and take the shape of the previously created mold
Amber
a fossilized resin (plant product) from ancient forests
Disconformity
when two sedimetary rock layers are separated by a rough/jagged boundary due to a lot of erosion taking place before the new sedimentary layer was deposited
Inclusion
fragments of older rock that are found within a younger igneous rock or coarse-grained sedimentary rock
Correlation
the matching of rocks from one geographic region to another region (geologists look for unique fossils or rock/mineral features)
Permineralization
the process by which pore spaces in an organism are filled in with mineral substances when a fossil is formed
Altered Hard Parts
fossils whose organic material has been removed and whose hard parts have been changed by recrystallization or mineral replacement
Original Preservation
describes a fossil with soft and hard parts that have not undergone any change since the organism's death
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