The evolutionary histories of Earth and Mercury differ fundamentally. The smallest planet, closest to the sun, likely began cooling early on, much like a setting pudding: As early as about 1 billion years after its formation, Mercury's volcanic activity came to a halt, and a solid, continuous "r...

Source: [Phys.org](https://phys.org/news/2026-08-mercury-crust-deeper-hotter-volcanic.html)

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