VOA科学技术2023--Study: Moon Is 40 Million Years Older than First Believed

Study: Moon Is 40 Million Years Older than First Believed

Scientists say a mineral found in moon dust suggests Earth's moon is 40 million years older than scientists had believed.

The finding was made by researchers who examined moon samples gathered by astronauts from the lunar surface in 1972 – the last time humans walked on the moon. The samples were part of a collection of 110 kilograms of dust and rock returned to Earth for scientific study.

The American space agency NASA says the leading theory on how the moon formed involves a huge crash. NASA says a Mars-sized object likely crashed into Earth and released material from both objects, which formed the moon.

But the exact timing¹ of when the moon was created has been difficult to identify. A new study based on the 1972 samples suggests the moon formed about 4.46 billion years ago.

The research was led by a team from the Field Museum of Natural History in Chicago, Illinois. The findings were recently published in a study in Geochemical Perspective Letters.

The study examined small crystals found in the lunar dust. The team said the crystals contained a mineral called zircon. The zircon is believed to have formed when the lunar surface cooled after being in a melting state after the crash.

The method used to estimate the age of the dust sample is called atom probe tomography. This method had not been developed when the sample was collected 51 years ago, said Philipp Heck. He is the lead writer of the study and the senior director of research at the Field Museum of Natural History.

NASA said the lunar sample was collected from an area known as the Taurus-Littrow valley on the near side of the moon. The near side of the moon is the side that always faces Earth. The sample had been stored at NASA's Johnson Space Center in Houston, Texas.

Heck noted² that zircon is a very strong mineral that can "survive the breakdown³ of rocks during weathering."

The new study followed an earlier one carried out in 2021. In that study, researchers examined how many atoms of uranium and lead were contained in the zircon crystals. They then estimated the age of the mineral based on differences in the decay of the radioactive uranium to lead over time.

But the purpose of the new study was to confirm the earlier study's results, which were not considered conclusive⁴. The examinations of the sample material were carried out atom-by-atom with very sensitive instruments, the researchers said.

Jennika Greer is a researcher in the School of Geographical⁵ and Earth Sciences at the University of Glasgow in Scotland. She helped lead the study. Greer told Reuters news agency the finding is "a great example of what the nanoscale, or even atomic scale, can tell us about big-picture questions."

Heck, from the Field Museum, said the huge crash that formed the moon was a major event that changed Earth's rotational⁶ speed. He added, "The formation date of the moon is important as only after that Earth became a habitable planet."

Greer said she hopes the team's finding can be a basis for answering many remaining questions about the moon. "It's amazing being able to have proof that the rock you're holding is the oldest bit of the Moon we've found so far." She added, "When you know how old something is, you can better understand what has happened to it in its history."

Words in This Story

sample – v. a small amount of something that gives you information about the thing it was taken from

crystal –n. a mineral that has formed into a regular shape because of the physical qualities of what it is made of

decay – v. to become weak or destroyed over time, often because of natural causes like bacteria or age

conclusive – adj. proving that something is true

scale – n. the size or level of something

habitable – adj. having the ability to support life

1 timing   

n.时间安排，时间选择

参考例句：

• The timing of the meeting is not convenient.会议的时间安排不合适。
• The timing of our statement is very opportune.我们发表声明选择的时机很恰当。

2 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。

3 breakdown   

n.垮，衰竭；损坏，故障，倒塌

参考例句：

• She suffered a nervous breakdown.她患神经衰弱。
• The plane had a breakdown in the air,but it was fortunately removed by the ace pilot.飞机在空中发生了故障，但幸运的是被王牌驾驶员排除了。

4 conclusive   

adj.最后的，结论的；确凿的，消除怀疑的

参考例句：

• They produced some fairly conclusive evidence.他们提供了一些相当确凿的证据。
• Franklin did not believe that the French tests were conclusive.富兰克林不相信这个法国人的实验是结论性的。

5 geographical   

adj.地理的；地区(性)的

参考例句：

• The current survey will have a wider geographical spread.当前的调查将在更广泛的地域范围內进行。
• These birds have a wide geographical distribution.这些鸟的地理分布很广。

6 rotational   

adj.回转的，轮流的

参考例句：

• A synchronous motor drives the measuring bob at a constant rotational speed.同步马达驱动测锤以恒速旋转。
• With some limitations,this is true also of rotational degrees of freedom.在某些限定条件下，这一说法对转动自由度也成立。