What process or event was required for plate retinues to begin on earth?

southern West Greenland, one team of researchers says that modern plate tectonics, with its subduction zones, spreading centers, earthquakes and all the other features we're familiar with, probably started about 3.2 billion years ago (the Earth is about 4.6 billion years old).

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poor water quality affects most estuarine organisms, including commercially important fish and shellfish. the pollutants that have the greatest impact on the health of estuaries include toxic substances like chemicals and heavy metals, nutrient pollution (or eutrophication), and pathogens such as bacteria or viruses.

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