Many fine-grained muds are deposited at a rate of about 1 cm/1000 years. At this rate, how long would it take to accumulate a sedimentary sequence half a kilometer thick?
Construct a cross section similar to the one at the top of Figure 8.10 to show the following sequence of geologic events: (a) deposition of a limestone formation; (b) uplift and folding of the limestone; (c) erosion of the folded rock; (d) subsidence and deposition of a sandstone formation.
How many formations can you count in the geologic cross section of the Grand Canyon in Earth Issues 8.1? How many are the same formations observed in Zion Canyon? Are any of the formations observed in both the Grand Canyon and the Bryce Canyon cross sections?
By comparing the sequence of formations illustrated in Earth Issues 8.1 with the relative time scale in Figure 8.11, identify a major disconformity in the Grand Canyon stratigraphic succession. Which periods of geologic time are missing? What is the minimum amount of geologic time, measured in millions of years, that is missing? (Hint: Consult Figure 8.15.)
What type of unconformity would probably be produced on a continental margin that was broadly uplifted above sea level and then subsided below sea level? What type of unconformity might separate young flat-lying sediments from older metamorphosed sediments?
Mass extinctions have been dated at 444 million years ago, 416 million years ago, and 359 million years ago. How are these events expressed in the geologic time scale of Figure 8.15?
A geologist discovers a distinctive set of fish fossils that dates from the Devonian period within a low-grade metamorphic rock. The rubidium-strontium isotopic age of the rock is determined to be only 70 million years. Give a possible explanation for the discrepancy.
Explain why the last eon of geologic time is named the Phanerozoic.
At the present rate of seafloor spreading, the entire seafloor is recycled every 200 million years. Assuming that the past rate of seafloor generation has been this fast or faster, calculate the minimum number of times the seafloor has been recycled since the end of the Archean eon.