44 How large is the crater created in southern Mexico by the asteroid 66m years ago?
(A)10km across in diameter.
(B)85km in diameter.
(C)7.4km in diameter.
(D)Not mentioned in the article. 

Some 66m years ago Earth was hit by a space rock reckoned(計算、判斷) to have been 10km across(寬). 

大約六千六百萬年前，地球被一個粗估直徑10公里的太空岩石所擊中。

The resulting chaos caused the extinction of dinosaurs and many other species, opening the way for the age of mammals－and ultimately humans. 

所造成的混亂導致了恐龍和許多其他物種的滅絕，開創哺乳動物的時代，最終為人類開闢了道路。

It also left a big hole in what is now southern Mexico. 

也在現今的墨西哥南部遺留下一個大洞。

That hole is one of only three known of similar dimensions (the other two are Vredefort in South Africa and Sudbury in Canada).

那個洞是僅有三個已知類似尺寸之一（另外兩個是南非的Vredefort和加拿大的薩德伯里）。

And this is odd. 

這很奇怪

For, during the billions of years that Earth has had a solid crust, many more than three big asteroids might have been expected to have hit it. 

因為在數十億年的時間裡，地球已經有了堅實的地殼，所以推測有三顆以上大型的小行星曾擊中過地球????。

Earth’s crust formed more than 4 billion years ago, but the oldest surviving blocks of it large enough to harbor craters date back only 3.5 billion years.

地殼形成了超過40億年前，但其最古老的、大到可留存下隕石坑的區塊，可以追溯到三十五億年。

What is known of the sizes and orbits of modern asteroids suggests that, if things have not changed over the aeons, about 14 big asteroids (defined as having a diameter of more than 7.4km, which would cause a crater at least 85km in diameter) should hit Earth every billion years. 

如果在這極漫長的時期裡都沒有改變，就已知的現代小行星的尺寸和軌道表明，每十億年約十四個大型小行星襲擊地球

That means 49, give or take seven, over the past 3.5 billion years. 

這意味，在過去35億年的時間裡，約49上下誤差7????

Such impacts may have been more common in the past, when more big asteroids were around. 

這樣的影響可能在過去更為常見，當時附近有更多的大型小行星。

Allowing for this, Earth would have been hit by 113, give or take 11, of them. 

假如同意這樣的說法，地球會被113(+-11)擊中????

Either way, a lot of craters are missing.

無論哪種方式，很多隕石坑都不見了。

That thought led Brandon Johnson of the MIT and Timothy Bowling of Purdue University in Indiana, to wonder how many other craters have vanished, either by erosion or by being swallowed into Earth’s interior as its crust moves around, and therefore whether it is likely that some have survived and been overlooked. 

這個想法使這兩人想知道有多少其他的隕石坑已經消失，不論是由於侵蝕或是當地殼移動時被吞沒到地球內部，而有多少倖存下來只是被忽視了?????

They have just published their analysis in Geology. 他們剛剛在地質學中發表了他們的分析

Earth’s crust formed more than 4 billion years ago, but the oldest surviving blocks of it large enough to harbor craters date back only 3.5 billion years.

地殼形成了超過40億年前，但其最古老的、大到可留存下隕石坑的區塊，可以追溯到三十五億年。

What is known of the sizes and orbits of modern asteroids suggests that, if things have not changed over the aeons, about 14 big asteroids (defined as having a diameter of more than 7.4km, which would cause a crater at least 85km in diameter) should hit Earth every billion years. 

如果在這極漫長的時期裡都沒有改變，就已知的現代小行星的尺寸和軌道表明，每十億年約十四個大型小行星襲擊地球

That means 49, give or take seven, over the past 3.5 billion years. 

這意味，在過去35億年的時間裡，約49上下誤差7????

Such impacts may have been more common in the past, when more big asteroids were around. 

這樣的影響可能在過去更為常見，當時附近有更多的大型小行星。

Allowing for this, Earth would have been hit by 113, give or take 11, of them. 

假如同意這樣的說法，地球會被113(+-11)擊中????

Either way, a lot of craters are missing.

無論哪種方式，很多隕石坑都不見了。

That thought led Brandon Johnson of the MIT and Timothy Bowling of Purdue University in Indiana, to wonder how many other craters have vanished, either by erosion or by being swallowed into Earth’s interior as its crust moves around, and therefore whether it is likely that some have survived and been overlooked. 

這個想法使這兩人想知道有多少其他的隕石坑已經消失，不論是由於侵蝕或是當地殼移動時被吞沒到地球內部，而有多少倖存下來只是被忽視了?????

They have just published their analysis in Geology. 他們剛剛在地質學中發表了他們的分析