If you wanted to consult the geologic period for when the first vertebrates evolved, where would you look?
a. in the section for the Ordovician period of the Paleozoic era.
b. in the section for the Quaternary period of the Cenozoic era.
c. in the section for the Triassic period of the Mesozoic era.
d. in the section for Precambrian time.
After a rock layer is eroded, which additional event must occur to create an unconformity, or a gap in the geologic record?
a. an earthquake or motion along a fault.
b. new deposits of sediment must build up on the eroded area.
c. folding of sedimentary rock layers.
d. a volcanic eruption.
A and A
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To consult the geological period for when the first vertebrates evolved, you would look in the section for the Ordovician period of the Paleozoic era. This time period occurred approximately 485 to 444 million years ago and is known for the diversification of marine life, including the appearance of the first vertebrates.
To create an unconformity, or a gap in the geologic record, an additional event must occur after a rock layer is eroded. The correct answer in this case is b. New deposits of sediment must build up on the eroded area. This is because the deposition of new sedimentary layers is required to fill in the gap left by the eroded rock layer, creating a discontinuity in the geological record. Unconformities can be useful indicators for understanding geological processes and identifying missing or incomplete rock sequences.
So, the correct answer for both questions is a and b, respectively.