In the last 40 years, astronomers have gathered more and more evidence that our moon came out of a scarcely-imaginable collision between a baby (100-million-year-old) Earth and another proto-planet named Theia. (Watch this video for a good explanation.) Just two weeks ago, astronomers at UCLA announced a clarification: Theia didn't hit Earth in a glancing blow, as previously thought. Instead, the two planets hit head-on:
“We don’t see any difference between the Earth’s and the moon’s oxygen isotopes; they’re indistinguishable,” said Edward Young, lead author of the new study and a UCLA professor of geochemistry and cosmochemistry.
The fact that oxygen in rocks on the Earth and our moon share chemical signatures was very telling, Young said. Had Earth and Theia collided in a glancing side blow, the vast majority of the moon would have been made mainly of Theia, and the Earth and moon should have different oxygen isotopes. A head-on collision, however, likely would have resulted in similar chemical composition of both Earth and the moon.
“Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them,” Young said. “This explains why we don’t see a different signature of Theia in the moon versus the Earth.”
So why am I reviewing catastrophic astronomical events? I'm reading Neal Stephenson's latest novel, Seveneaves, which posits (in its opening paragraph) the collision between our moon and what is probably a small black hole. Stephenson imagines what would happen from a serious, scientific perspective.
Seveneves isn't what you would call a character piece. I'm 45% through it, according to my Kindle, and thoroughly fascinated. But Stephenson is almost the anti-Ishiguro.
Another aside: I have to see the tidal bore in the Bay of Fundy someday. It just sounds so cool—especially in context.