Earth and Space Chapter 12

What ideas do geologists use as they study Earth?
the rock record provides evidence of past geological events and life forms, processes in the present acted in the past, Earth is very old and has changed over time
In what type of rocks would geologists most likely find evidence of past life forms?
sedimentary rocks
The geological processes that shape Earth’s features today…
are basically the same as they were in the geologic past
The physical, chemical, and biological laws that operate today have also operated in the geologic past. This statement relates to the principle of…
uniformitarianism
According to the principle of cross-cutting relationships, an intrusive rock body is…
younger than the rocks into which it intrudes
The dating process that places geologic events in proper sequence is referred to as a…
relative dating
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In general, the law of superposition states that in an undeformed sequence of sedimentary rocks, each layer is…
older than the one above it
Which type of geologic event has to occur to create an angular conformity?
folding and tilting of rock layers, followed by renewed deposition
An unconformity is a…
gap in the rock record
Fossils are the…
remains and traces of prehistoric life
In what type of rocks are most fossils found?
sedimentary rocks
What environment would NOT contain fossils?
intrusive rock formed from cooled magma
What determines the type of fossil that is formed?
the conditions under which the organism died and how it was buried
What is important if an organism is to become a fossil?
rapid burial and hard parts
Why would a worm stand a poor chance of being fossilized?
worms have no hard parts
The task of using fossils to match up rocks of similar ages in different areas is called…
correlation
Index fossils allow geologists to…
match up rocks of the same age in different regions
The process by which atomic nuclei spontaneously decay is called
radioactivity
The time it takes for 50% of the nuclei in a radioactive sample to decay to its stable isotope is called…
a half-life
According to the theory of evolution, organisms change over time because of a process called…
natural selection
Which two substances do geologists use in radiocarbon dating?
carbon-14 and carbon-12
Based on interpretations of rock units and changes in fossil life forms, geologists have divided Earth’s history into manageable units that are represented by the…
geographical time scale
What is the currently accepted age of Earth?
about 4.6 billion years old
The largest expanse of time on the geologic time scale is the…
eon
What is the division of the geologic time scale in order from longest to shortest?
era, period, epoch
About 88 percent of Earth’s history is within the expanse of time before the Phanerozoic era called the…
Precambrian
Radiometric dating does not usually work with sedimentary rock because they
form from many older rock particles