are basically the same as they were in the geologic past
The geological processes that shape Earth's features today _____.
James Hutton
What scientist is credited with proposing the principle of uniformitarianism?
younger than the rocks into which it intrudes
According to the principle of cross-cutting relationships, an intrusive rock body is _____.
remains or traces of prehistoric life
Fossils are the _____.
sedimentary rocks
In what type of rocks are most fossils found?
altered remains
Petrified wood is an example of what type of fossil?
sedimentary rocks
In what type of rocks would geologists most likely find evidence of past life forms?
uniformitarianism
The physical, chemical, and biological laws that operate today have also operated in the geologic past. This statement relates to the principle of ____.
older than the one above it
In general, the law of superposition states that in an undeformed sequence of sedimentary rocks, each layer is ____.
the sandstone
If a layer of sandstone is in contact with a mass of granite that contains small pieces of the sandstone, which rock is older?
angular unconformity
What type of unconformity consists of tilted sedimentary rocks that are overlain by younger, more flat-lying sedimentary rocks?
the conditions under which the organism died and how it was buried
What determines the type of fossil that is formed?
rapidly buried by sediments
Organisms with hard parts stand a good chance of being fossilized if they are ____.
fish
Which of these organisms would have the best chance of becoming part of the fossil record?
4.6 billion years
What length of time does the geologic time scale cover?
eon
The largest expanse of time on the geologic time scale is the _____.
Phanerozoic
Which eon of the geologic time scale means "visible life"?
break apart
Radioactivity is produced when unstable nuclei ____.
the half-life
The time it takes for 50% of the nuclei in a radioactive sample to decay to its stable isotope is called ____.
a date for when the rock formed
The radiometric dating of an igneous rock provides ____.
carbon-14 and carbon-12
Which two substances do geologists use in radiocarbon dating?
geologic time scale
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 ____.
about 4.6 billion years old
What is the currently accepted age of Earth?
Paleozoic
The era of "ancient life" is known as the ____.
540 million years ago
When did abundant fossil evidence appear in the geologic record?
Gondwana
During the early Paleozoic era, South America, Africa, Australia, Antarctica, India, and perhaps China comprised the vast southern continent of _____.
They fused into Pangaea.
What happened to all the continents by the close of the Paleozoic?
seas
In the early Paleozoic, life was restricted to the _____.
Dinosaurs
What animals dominated the Mesozoic Era?
birds
One group of reptiles, characterized by the fossil Archaeopteryx, led to the evolution of _____.
a meteorite collision
What likely contributed to the extinction that marks the end of the Mesozoic Era?
Quaternary
Which period represents the last 2 million years of geologic time?
plate interactions
What caused many events of mountain building, volcanism, and earthquakes in western North America during the Cenozoic?
age of mammals
Which title best describes the current geologic age?