Name: 撞擊地球最大的小行星是什麼？ (What Were the Biggest Asteroids to Hit Earth?)
Uploaded: 2021-01-14T05:49:09.000Z
Duration: 2 min 56 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

>> Denton Ebel: We think—and a lot of evidence supports this theory—that the Earth’s

情態副詞

moon formed in a large collision, probably only one collision, between the Earth and

程度副詞

a Mars-size object, very early, within 60 million years of the Earth really accreting

and differentiating into a core and a mantle.

We know from Mercury, from the moon, that there were many large impacts in the early

When you look at the moon and you see these big, dark patches that are roundish, those

Huge impact basins that are filled with lava from inside the moon.

So, we can use the moon as a measuring rod for the impact history of the Earth

And, of course, we’re familiar with the asteroid that hit the Earth 65 million years ago

ago, causing a huge crater in the Caribbean.

Evidence from this impact has been found around the world as a thin, sedimentary layer called

the Cretaceous-Paleogene boundary, or K-Pg for short.

Geologists discovered that this layer is rich in metallic elements like iridium, that are

rare on the crust and mantle of the earth because they’ve been concentrated in the

core, but they’re common in asteroids and comets because those bodies

The reason geologists made that distinction between the cretaceous period and the Paleogene

is this huge change in the nature of life itself: where mammals take over,

But, more importantly, at the plankton level—the small, small creatures, the small life forms,

which make very nice sediments that are dateable,

it’s like a knife edge in the record of life itself.

As a result of a cosmic collision—an accident really.

Something that happens every so often, and we hope doesn’t happen to us.