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USGS CMG InfoBank: Age of Ocean Crust

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Comment: 09:45 - 10:39 (00:54)
Source: Annenberg/CPB Resources - Earth Revealed - 4. The Sea Floor
Keywords: crust, fossil, Australia, stromatolite, "James Sadd"

Our transcription: The fact that there is no ocean crust on Earth older than 200 million years raises an intriguing question.
Does this mean that oceans didn't exist on Earth during the preceding 4.4 billion years of Earth history?
Clearly, this can't be true.
Fossils of organisms that lived in the sea are found in rocks older than 200 million years on every continent on Earth.
In fact, fossils of multicellular marine animals range in age back at least 670 million years, and evidence of colonial marine algae, called "Stromatolites" have been found in the oldest sedimentary rocks on Earth.
Discovered in Northwest Australia, these sedimentary rocks and the stromatolites they contain are definitely of marine origin and range in age between 2.8 and 3.5 billion years.
If, then, oceans did exist throughout most of Earth history, what has happened to all of the old ocean crust?

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