According to the diagram, what key event first occurred in the Archean Eon?

The Archean Eon began after Earth had formed, and it is associated with the development of Earth's early crust. Earth's accretion occurred earlier, during the Hadean Eon; dinosaurs appeared much later, and ocean evaporation is not the key event shown for the Archean. Therefore, crust formation is the correct choice.

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