The Precambrian eon is separated from the Phanerozoic eon in the fossil record because of the sudden appearance of organisms.
Explanation:
Precambrian eon is the initial existence on earth that can be predicted by the study of rocks and remaining of fossils. It has been seen as the existence of skeleton in this era, before this era no such things has been observed, even the development of sexual reproduction.
The Phanerozoic era comes after the Precambrian era, more advanced kinds of fossils of animals had been observed in this era. Phanerozoic era period of life on earth. Large organisms sudden appearance are seen in the Phanerozoic era i.e. First dinosaurs, mammals, fishes, angiosperms,first vertebrates etc.
The best description of predictable development of plant structure in an area over time is primary succession. The correct option is a.
<h3>What is succession?</h3>
Changes in the physical environment and the population of the species cause succession. There are two types of succession: primary and secondary succession.
Nudation, invasion, competition and coaction, reaction, and stabilization are the five stages of ecological succession. Autogenic succession is derived by biotic factor in an ecosystem.
Thus, the correct option is a. primary succession.
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The fossils that provide information on the formation of an oxygen-rich atmosphere are the stromatilites from the Precambrian era. These are layered and columnar fossils consisting mainly of cyanobacteria which were the original life form back then. These bacteria took in carbon dioxide and produced oxygen by photosynthesis as early as 2.5 billion years ago (the earth is about 4.5 billion yrs old).
