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Title: When did modern plate tectonics begin on Earth?
Plain: Proposed start dates range from more than 4 billion years ago to under 1 billion years ago. Old rocks are scarce and can be read in more than one way.
Precise: Date the onset of a global mobile-lid regime with deep subduction. Proposals range from about 4.2 Ga (Hadean zircon chemistry) through about 3.2 to 2.5 Ga (geochemical transitions, paleomagnetic relative motion) to about 0.8 Ga (first widespread blueschists and ultrahigh-pressure rocks). An answer is an onset age, or a demonstration of continuous operation since the Hadean, consistent with petrological, geochemical and paleomagnetic records.
Settled by: Paleomagnetic proof of differential motion between Archean cratons together with petrological evidence of cold, deep subduction in dated rocks.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: contested
Status note: (empty)
Posed since: (empty)