Question 1: [5] The oxygen buildup was probably due to two factors: a filling of the chemical sinks, and an increase in ________ burial, which sequestered organic compounds that would have otherwise been oxidized by the atmosphere.
Question 2: Classically, the boundary between the Proterozoic and the Phanerozoic eons was set at the base of the ________period when the first fossils of animals including trilobites and archeocyathids appeared.
Question 3: In the second half of the 20th century, a number of fossil forms have been found in Proterozoic rocks, but the upper boundary of the Proterozoic has remained fixed at the base of the ________, which is currently placed at 542 Ma.
Question 4: Red beds, which are colored by ________, indicate an increase in atmospheric oxygen after 2 billion years ago; they are not found in older rocks.
Question 6: The Proterozoic (pronounced /ˌproʊtərəˈzoʊɪk/) is a geological eon representing a period before the first abundant complex life on ________.
Question 9: The Mackenzie dike swarm in Canada's ________ is the largest known dike swarm on Earth, and was a source for significant massive flood basalt eruptions throughout the Proterozoic period.
Question 10: The Proterozoic Eon extended from 2500 Ma to 542.0 ± 1.0 Ma (million years ago), and is the most recent part of the old, informally named ‘________’ time.
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