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  • 4 years ago

Please answer essay question? I did every other question on this test but for the life of me cannot get this one! It is attached as a picture.

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  1. anonymous
    • 4 years ago
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  2. Koikkara
    • 4 years ago
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    From my point of view.....The Precambrian (Pre-Cambrian) is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale. It spans from the formation of Earth about 4570 Ma (million years) ago to the beginning of the Cambrian Period, about 541.0 ± 1.0 Ma, when macroscopic hard-shelled animals first appeared in abundance. The Precambrian is so named because it precedes the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the classical name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of geologic time. See Timetable of the Precambrian. a) Proterozoic: this eon refers to the time from the lower Cambrian boundary, 541.0 ± 1.0 Ma, back through 2500 Ma. As originally used, it was a synonym for "Precambrian" and hence included everything prior to the Cambrian boundary. The Proterozoic eon is divided into three eras: the Neoproterozoic, Mesoproterozoic and Paleoproterozoic. b) Neoproterozoic: The youngest geologic era of the Proterozoic Eon, from the Cambrian Period lower boundary (541.0 ± 1.0 Ma) back to 1000 Ma. The Neoproterozoic corresponds to Precambrian Z rocks of older North American geology. c) Ediacaran: The youngest geologic period within the Neoproterozoic Era. The "2012 Geologic Time Scale" dates it from 541.0 ± 1.0 to ~635 Ma. In this period the Ediacaran fauna appeared. d) Cryogenian: The middle period in the Neoproterozoic Era: ~635-850 Ma. e) Tonian: the earliest period of the Neoproterozoic Era: 850-1000 Ma. f) Mesoproterozoic: the middle era of the Proterozoic Eon, 1000-1600 Ma. Corresponds to "Precambrian Y" rocks of older North American geology. Paleoproterozoic: oldest era of the Proterozoic Eon, 1600-2500 Ma. Corresponds to "Precambrian X" rocks of older North American geology. Archean Eon: 2500-4000 Ma. Hadean Eon: 3950-4500 Ma. This term was intended originally to cover the time before any preserved rocks were deposited, although some zircon crystals from about 4400 Ma demonstrate the existence of crust in the Hadean Eon. Other records from Hadean time come from the moon and meteorites. Paleozoic Era In geologic time , the Paleozoic Era, the first era in the Phanerozoic Eon , covers the time between roughly 544 million years ago (mya) and until 245 mya. The Paleozoic Era spans six geologic time periods including the Cambrian Period (544 to 500 mya); Ordovician Period (500 mya to 440 mya); Silurian (440 mya to 410 mya); Devonian (410 mya to 360 mya); and the Carboniferous Period (360 mya to 286 mya) (in many modern geological texts, especially those in the United States, the time of Carboniferous Period is covered by two alternate geologic periods, the Mississippian Period [360 mya to 325 mya] and the Pennsylvanian Period [325 mya to 286 mya]. The final geologic time period in the Paleozoic Era is the Permian Period (286 mya to 245 mya). Paleozoic Era: The onset of the Paleozoic Era is marked by the "Cambrian explosion," the sudden appearance of numerous fossils . Although life certainly started in Precambrian time, The start of the Paleozoic Era marks the point at which life developed to a variety or organisms capable of leaving fossils. Although fossilization is difficult under any circumstances, organisms with structures such as shells have a much greater chance of leaving fossilized remains than did single celled microorganisms. The Paleozoic Era spanned that period of geologic time during which the evolution of the first invertebrates, vertebrates, terrestrial (land-based) plants, bony fish, reptiles, insects, etc. took place. The end of the Paleozoic Era (approximately 245 mya) marks the largest mass extinction of species in Earth's history. During this mass extinction an estimated 90% of all Earth's marine species suddenly became extinct. Six major continental landmasses developed during the Paleozoic Era. Although not located in their present global positions, parts of the modern continents can be traced to these landmasses. For example, continental crust now located in the North American continent was located near the equator during the Paleozoic Era. The forces of plate tectonics were active, and not only moved the continents but helped shape the continental margins though uplift and subduction. Enormous changes on sea state relative to the continents meant extensive flooding, marine transgression , and marine regression that added large sedimentary deposits (e.g., large limestone deposits). The abundance of organic life provided the start for abundant coal formation during the Carboniferous Period (Pennsylvanian Period and Mississippian Period).

  3. Koikkara
    • 4 years ago
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    you just need to pick out major facts-as points and complete accordingly...hope, this help you....

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