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The stability of liquid water (that is, its continuous presence on Earth) implies that surface seawater temperatures were similar to those of the present.Differences in the chemical composition of Archean and Proterozoic sedimentary rocks point to two different mechanisms for controlling seawater composition between the two Precambrian eons.Several rock types yield information on the range of environments that may have existed during Precambrian time.Evolution of the atmosphere is recorded by banded-iron formations (BIFs), paleosols (buried soil horizons), and red beds, whereas tillites (sedimentary rocks formed by the lithification of glacial till) provide clues to the climatic patterns that occurred during Precambrian glaciations. This follows from the fact that the continents are distributed at different latitudes, and latitudinal position affects the temperature of oceanic waters along continental margins (the combined area of the continental shelf and continental slope); in short, sedimentary deposition is climatically sensitive.Nevertheless, the original terminology to distinguish Precambrian rocks from all younger rocks is still used for subdividing geologic time.

Oceans of the Archean Eon (4.0 to 2.5 billion years ago) contained much volcanic-derived ferrous iron (Fe) in BIFs.It can also be inferred that stromatolite-bearing dolomites of Riphean rock, a sedimentary sequence spanning the period from 1.65 billion to 800 million years ago, were deposited in warm, tropical waters.Riphean rock is primarily located in the East European craton, which extends from Denmark to the Ural Mountains, and in the Siberian craton in Russia.It was denoted by the first appearance of animal life (metazoans) requiring sufficient oxygen for the production of collagen and the subsequent formation of skeletons.Furthermore, in the stratosphere during the Precambrian, free oxygen began to form a layer of ozone (O The origin of Earth’s oceans occurred earlier than that of the oldest sedimentary rocks.The 3.85-billion-year-old sediments at Isua in western Greenland contain BIFs that were deposited in water.These sediments, which include abraded detrital zircon grains that indicate water transport, are interbedded with basaltic lavas with pillow structures that form when lavas are extruded under water.During the long course of Precambrian time, the climatic conditions of the Earth changed considerably.Evidence of this can be seen in the sedimentary record, which documents appreciable changes in the composition of the atmosphere and oceans over time.These relatively high concentrations were sufficient for oxidative weathering to take place, as evidenced by hematite-rich fossil soils (paleosols) and red beds (sandstones with hematite-coated quartz grains).A second major peak, which raised atmospheric oxygen levels to 50 percent PAL, was reached by 600 million years ago.

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  1. Precambrian time Precambrian time. and red beds of Phanerozoic age dating back to the Cambrian have a similar bimodal. This relative shortage of volcanoes.

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