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Earth is the only planet we know of that has green, silky continents. But, despite decades of research, geologists still don’t agree on how they were formed. “Continents began to form about four billion years ago—they are the oldest known world rocks,” said Tim Johnson, a geologist at Curtin University in Perth, Australia. “The Earth is four and a half billion years old, so why it began to appear at that time is not known, as it is the formation of the continental crust.”
Johnson and his colleagues now argue that the formation of the Earth’s continents was largely caused by an asteroid impact that made the early crust hot and thin enough to allow the continents to move. In short, the worlds we live in are here because of ancient bombs from space.
Leaves and leaves
The problem with studying the formation of continents is that the geological evidence for this process is almost complete. The oldest known continental rocks appeared 4.03 billion years ago, at the end of the Hadean eon (the oldest period in the history of the Earth, since its 500 million years of existence). The rare basaltic rocks date back to about 4.2 billion years, and a few of the oldest crystals push that date to 4.4 billion years. Beyond that, nothing else. Therefore, scientists who researched the origins of the continents had to rely heavily on academic fiction. “There’s a lot of controversy about what’s going on in the early world, because a lot of it is rare,” Johnson said.
