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Science chapter 12
Terms in this set (41)
Sedimentary rocks record past geological events and _________?
changing life forms of the past
In what type of rocks would geologists most likely find evidence of past life forms?
An example of a geologic event that could be recorded in rocks is_______?
a volcanic eruption
The physical, chemical, and biological laws that operate today have also operated in the geologic past. This statement relates to the principal of__________?
According to the principle of cross-cutting relationships, an intrusive rock body is_______?
younger than the rocks into which it intrudes
Nicolaus Steno proposed the most basic principle of relative dating, the law of______?
The dating process that places geologic events in proper sequence is referred to as a________?
In general, the law of superposition states that in an undeformed sequence of sedimentary rocks, each layer is_______?
older that the one above it
What is the youngest feature shown in Figure 12-1?
igneous intrusion L
Which of the following sequences correctly lists the geologic events in figure 12-1 in order from oldest to youngest (oldest listed first)
What type of unconformity consists of titled sedimentary rocks that are overlain by younger, more flat-laying sedimentary rocks?
An unconformity is a(n)_______?
gap in the rock record
Fossils are the______?
remains or traces of prehistoric life
In what type of rocks are most fossils found?
Which of the following environments would most likely NOT contain fossils?
Intrusive rock formed from cooled magma
Petrified wood is an example of what type of fossil?
The footprints of a dinosaur are an example of what type of fossil?
Which of the following 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
Which of these organisms would have the best chance of becoming part of a fossil record?
The task of using fossils to match up rocks of similar ages in different areas is called_______?
Which of the following must be true for a fossil organism to be useful as an index fossil?
All of the above: the fossil organism must be widespread geographically.
The fossil organism must be abundant.
The fossil organism must be limited to a short span of geologic time.
Groups of fossil plants and animals succeed each other in a definite and determinable order, and any period of geologic time can be recognized by its respective fossils. This is a statement of the_______?
Principle of fossil succession
The process by which atomic nuclei spontaneously decay is called_______?
The time it takes for 50% of the nuclei in a radioactive sample to decay to its stable isotope is called________?
According to figure 12-2, what fraction of the original parent isotope still exists after 4 half-lives have passed?
A sample is brought to the laboratory and its determined that one-eighth of the original parent isotope remains in the sample. Use the figure 12-2 to determine the age of the sample if the half-life of the material is 60 million years.
180 million years old
If the half-life of an unstable isotope is 10,000 years, and only 1/8 of the radioactive parent remains in a sample, how old is the sample?
30,000 years old
Which 2 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_______?
Geologic time scale
What is the currently accepted age of the Earth?
about 4.6 billion years old
The largest expanse of time on the geologic time scale is the_______?
About 88 percent of Earth's history is within the expanse of time before the Phanerozoic Era called the_______?
Radiometric dating does not usually work with sedimentary rocks because they________?
Form from many older rock particles
The principle of __________ states that physical, biological, and chemical processes we observe today have also operated in the geologic past.
____________ tells geologists the sequence, or order, in which events occurred.
The remains or trace of prehistoric life are called__________?
Fossils rarely preserve the ____________ parts of animals because scavengers often eat them and bacteria decompose them.
Great worldwide changes in forms of ________ on Earths mark the boundaries of eras.
The _________ is the era of "recent life" on Earth.
It is hard to use radiometric dating to tell the age of ________ rocks because the age of the particles in them may not represent when the rocks actually formed.
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