英語(yǔ)聽(tīng)力：自然百科 永恒的鉆石（二）

"The secret of the diamond lies in the carbon bond. Carbon is one of the most plentiful substances known to science. We find carbon in plants, animals and our bodies. Carbon everywhere. And yet diamonds are some of the rarest, most beautiful of all substances. What's the link? The link is the extremely rare environmental conditions that take ordinary carbon--coal, for example--and turn it into diamonds. We’re talking about deep inside the earth crust. We have the pressures, the temperatures, sufficient to distort the bonding angles of the carbon atoms."

Diamonds are not forged in the earth crust, where most other rocks are made. They come from much deeper, from a hundred miles within the earth's interior. And occasionally in bursts of intense violence, this buried treasure rockets to the surface, carried by special high-speed volcanoes.

To geologist Larry Taylor at the University of Tennessee, diamonds are a treasure trove, but not because of their beauty.

"This is the only hard samples we have of the deep interior of the earth. The diamonds are telling us something. They are telling us a story. So it's understanding the story that's being told by these minerals which is at the key to all understanding of our knowledge of the earth.

"We consider ourselves to be geologic detectives. We try to recreate the crime after the fact. We look at the diamonds and we try to figure out exactly how they formed, where they formed, why they formed."

But the diamonds themselves reveal very little. Even their age has been a source of scientificcontroversy. Most rocks and minerals can be dated because they contain certain radioactive atoms. As these atoms decay, they reveal their age. But diamonds never decay. Their chemistry is so stable, their internal bonds so tight, nothing inside the diamond changes. A diamond never grows old.

Inside a diamond, the bonds between atoms of carbon are the strongest known. This makes diamonds not only the world's hardest substance, but four times harder than the next hardest material.

Like amber encasing an insect, diamonds sometimes capture bits of surrounding minerals.Geologists call these fragments “inclusions”.

"The inclusion occurs inside the diamond. Everything around the diamond has changed its complete integrity. It’s changed everything about it, its chemistry, but the little inclusion inside has remainedpristine and virginal to this day. And this is the little piece of material that we are looking for."

Using high-resolution X-ray tomography, a technique similar to a CAT scan, Taylor and his team create a three-dimensional map of the volcanic rock, the diamonds and the inclusions inside. They may contain garnets, or sulfide minerals and other substances that can only be formed at hundreds of thousands of atmospheres. Analyzing these minerals reveals one of diamonds' astonishing secrets.

"It’s best we can tell, the inclusions that are inside a diamond date the diamond as being approximately somewhere between two and three billion years old."

At three billion years old, diamonds are among the earth's oldest creations. They are time capsules, carrying information and mystery. To Taylor, a diamond's true value is in what it can tell us about the distant past and the inner workings of the planet.