One argument against the comet theory is that a comet would have left a large hole in the Earth's surface.
VOA: special.2009.01.20
Suppose the planet were hit by a comet-- this happened--something like this happened sixty-five million years ago, so it could happen again.
假设这个星球被一颗彗星击中-,这样的事,大约六千五百万年前,发生过,所以它还可能再发生。
Nanodiamonds are produced under only a very high temperature and high pressure event, such as a comet striking Earth.
VOA: special.2009.01.20
In that event,astronomers were able to observe the icy comet long before it struck the solar system's biggest planet.
VOA: special.2009.08.25
Scientists at the Goddard Space Flight Center in Greenbelt,Maryland, found the substance glycine in material brought back to Earth from a comet.
VOA: special.2009.09.30
But the object that struck Jupiter in July is estimated to have been much smaller and harder to see than comet Shoemaker-Levy.
VOA: special.2009.08.25
Stardust passed through a cloud of material surrounding comet Wild Two in January of two thousand four.
VOA: special.2009.09.30
Since then, scientists around the world have been working to identify substances gathered from Comet Wild-Two.
VOA: special.2009.09.30
A comet is a huge ball of frozen gas and dust that often releases a long trail of material as it nears the sun.
VOA: special.2009.09.30
A specially designed collector gathered dust particles from the comet and stored them on the spacecraft.
VOA: special.2009.09.30
On February fourteenth, Stardust will approach to within two hundred kilometers of comet Temple 1.
VOA: special.2011.02.09
But it is the first time an amino acid has been discovered on a comet.
VOA: special.2009.09.30
She said the discovery "supports the theory that some of life's ingredients formed in space and were delivered to Earth long ago by meteorite and comet impacts."
VOA: special.2009.09.30
But scientists think it was either a comet or rock from space.
VOA: special.2009.08.25
Comet Shoemaker-Levy Nine broke up and struck Jupiter.
VOA: special.2009.08.25
Many scientists dismiss the comet theory.
VOA: special.2009.01.20
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