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A GEOLOGIST AS A DETECTIVE
Transcript of A GEOLOGIST AS A DETECTIVE
STATE THE PRINCIPLE OF UNIFORMITARIANISM
APPLY THE LAW OF SUPERPOSTION
COMPARE THE TYPES OF UNCONFORMITIES A GEOLOGIST AS A DETECTIVE Geologists estimate that
the earth is about 4.6 billion years old.
Hutton's principle of uniformitarianism states that current geologic processes, such as volcanism and erosion, are the same processes that were at work in the past.
Layers of rocks, called strata, are like the pages in a history book, detailing the sequence of events that took place in the past.
Using a few basic principles, scientists can determine the order in which rock layers were formed.
The law of original horizontality states that sediments deposited in water form flat, level layers parallel to the Earth's surface.
LAW OF SUPERPOSITION:
Is the idea that the bottom
layer of a series of sedimentary layers is the oldest, unless it has been overturned or older
rock has been thrust over it. In general, a rock layer is older than any joint, fault, or fold that appears in it; the rock had to already exist in order to be folded or faulted.
By unfolding or unfaulting the rock layers, one can determine their positions before they were disturbed.
The principle of superposition can then be applied to determine relative ages.
Igneous intrusions form when molten rock forces its way into preexisting rock, cools, and hardens.
Thus, an intrusion is younger than any rock it cuts through.
Extrusions form during volcanic eruptions when molten rock flows out onto the Earth's surface as lava and hardens, or is blown into the atmosphere and settles on the ground, forming a blanket of volcanic rock particles.
Thus, extrusions are younger than the rocks beneath them, but older than any layer that may form over them.
A break in the geologic record is called an unconformity.
An unconformity indicates that for a period of time deposition stopped, rock was removed by erosion, and then deposition resumed.