澳大利亚陨石中发现地球上最古老物质:来自70亿年前的星尘

Scientists say they have identified the oldest solid material on Earth – stardust believed to have formed about 7 billion years ago. It was found in pieces of meteorite¹ that fell out of the sky in Australia 50 years ago.

Stardust is matter that forms as small particles in space when stars die. These particles can be used later to form new planetary bodies, including stars, planets and moons.

The meteorite pieces came down in September 1969 in the town of Murchison, in Australia's Victoria state. Scientists with the Field Museum of Natural History in the American city of Chicago have long held the largest collection of these pieces.

But until now, the age of the oldest stardust samples had not been confirmed.

Researchers at the museum reported their identification last week in Proceedings² of the National Academy of Sciences.

"This is one of the most exciting studies I've worked on," said Philipp Heck, a curator at The Field Museum who led the research. "These are the oldest solid materials ever found, and they tell us about how stars formed in our galaxy³," he added.

The scientists said the microscopic⁴ particles were made of silicon⁵ carbide, the first mineral formed when a star cools. All of the samples predate the formation of our own solar system, they noted⁶.

The researchers said the stardust particles "became trapped in meteorites⁷, where they remained unchanged for billions of years." This makes the samples "time capsules" of events that happened before the solar system.

The identification process first involved crushing the samples down into a fine dust. The pieces were then mixed with acid, which left only the pre-solar particles.

The researchers then examined samples for information that would help them identify what kinds of stars they came from and how old they were.

In space, dust interacts with cosmic rays -- high-energy particles that move through space at nearly the speed of light.

Philipp Heck explained that some of these interactions result in the formation of new elements. The longer the interactions last, the more elements are formed. Age can then be estimated by measuring how many of the new cosmic ray-produced elements were present in pre-solar samples, Heck said.

Based on examinations of this data, the researchers learned that some of the pre-solar particles were the oldest ever discovered. The team identified the age of 40 grains, most of which were estimated to be between 4.6 billion and 4.9 billion years old.

These ages relate to the time when the first stars began to break up. Since that kind of star lived for up to 2.5 billion years, the stardust can be as old as up to seven billion years.

The latest dating process confirms a scientific theory that predicted "a baby boom of stars" happened before the formation of our sun.

"We have more young grains than we expected," Heck said. He added: "We basically came to the conclusion that there must have been a time in our galaxy when more stars formed than normal, and at the end of their lives they become dust producing."

Words in This Story

meteorite – n. a piece of rock from outer space

sample – n. a small amount of something that represents what it is like

curator – n. a person who is in charge of a museum

time capsule – n. a container filled with objects considered to be typical of a period in history and buried, so that it can be dug up and studied much later

interact – v. to act upon one another

baby boom – n. a large increase in the number of babies born in a particular place during a particular time

grain – n. a very small piece of a hard substance

conclusion – n. a decision made after a lot of consideration

1 meteorite   

n.陨石；流星

参考例句：

• The meteorite in Jilin Exhibition Hall is believed to be the largest in the world.吉林展览馆的陨石被认为是世界上最大的。
• The famous Murchison meteorite smashed into the Australian ground in 1969.1969年著名的默奇森陨石轰然坠落在澳大利亚。

2 proceedings   

n.进程，过程，议程；诉讼(程序)；公报

参考例句：

• He was released on bail pending committal proceedings. 他交保获释正在候审。
• to initiate legal proceedings against sb 对某人提起诉讼

3 galaxy   

n.星系；银河系；一群(杰出或著名的人物)

参考例句：

• The earth is one of the planets in the Galaxy.地球是银河系中的星球之一。
• The company has a galaxy of talent.该公司拥有一批优秀的人才。

4 microscopic   

adj.微小的，细微的，极小的，显微的

参考例句：

• It's impossible to read his microscopic handwriting.不可能看清他那极小的书写字迹。
• A plant's lungs are the microscopic pores in its leaves.植物的肺就是其叶片上微细的气孔。

5 silicon   

n.硅(旧名矽)

参考例句：

• This company pioneered the use of silicon chip.这家公司开创了使用硅片的方法。
• A chip is a piece of silicon about the size of a postage stamp.芯片就是一枚邮票大小的硅片。

6 noted   

adj.著名的，知名的

参考例句：

• The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。
• Jim is noted for arriving late for work.吉姆上班迟到出了名。

7 meteorites   

n.陨星( meteorite的名词复数 )

参考例句：

• Small meteorites have left impact craters all over the planet's surface. 这个行星的表面布满了小块陨石留下的撞击坑。 来自《简明英汉词典》
• One theory about the existence of extraterrestrial life rests on the presence of carbon compounds in meteorites. 地球外存在生命的理论是基于陨星上存在碳化合物质这一事实的。 来自《简明英汉词典》