Lunar dust collected by Apollo 17 astronauts in the 1970s has revealed that the Moon is 40 million years older than previously believed. After landing on the moon Dec. 11, 1972, NASA astronauts Eugene Cernan and Harrison Schmitt collected rocks and dust from the lunar surface. A new analysis of that sample detected zircon crystals and dated them to 4.46 billion years old. Previous estimates put the Moon, formed by a massive celestial collision, at 4.425 billion years old. The findings were published Monday in the journal Geochemical Perspectives Letters. “These crystals are the oldest known solids that formed after the giant impact. And because we know how old these crystals are, they serve as an anchor for the lunar chronology,” said senior study author Philipp Heck, Robert A. Pritzker Curator for Meteoritics and Polar Studies at the Field Museum of Natural History in Chicago, in a statement. The early days of our solar system — when Earth was still forming and growing in size — were chaotic, with rocky bodies often colliding in space. During that time more than 4 billion years ago, a Mars-size object crashed into Earth, flinging off a large rocky piece that became the Moon, according to the researchers. But scientists have struggled to precisely date this pivotal event. The energy from the impact of the Mars-size object hitting Earth melted the rock that would eventually form the Moon’s surface. “When the surface was molten like that, zircon crystals couldn’t form and survive. So any crystals on the Moon’s surface must have formed after this lunar magma ocean cooled,” said Heck, who is also the senior director of the museum’s Negaunee Integrative Research Center and a professor in the department of geophysical sciences at the University of Chicago. This research marks the first use of the analytical method of dating the crystals with atom probe tomography and was carried out using instruments at Northwestern University in Evanston, Illinois, according to the study authors. The analysis showed how many uranium atoms within the zircon crystals experienced radioactive decay. Elements can transform if their atoms contain an unstable configuration of protons and neutrons, causing some of them to decay — such as how uranium decays to become lead. By tracking how long this process takes, scientists can determine the age of something by comparing the ratio of uranium to lead atoms. The research team used lead isotopes within the lunar dust sample to determine that the crystals were 4.46 billion years old, indicating that the Moon must also be at least that old.(SD-Agencies) Words to Learn 相關(guān)詞匯 【巖漿】yánjiāng magma molten rock material 【關(guān)鍵】guānjiàn pivotal central and important 阿波羅17號宇航員20世紀(jì)70年代收集的月壤顯示，月球的年齡比之前認(rèn)為的要早4000萬年。 1972年12月11日登陸月球后，NASA宇航員尤金?塞爾南和哈里森?施密特收集了月球表面的巖石塵埃。一項新研究對這些樣本進行分析后檢測到了鋯石晶體，它們已經(jīng)存在了44.6 億年。之前認(rèn)為月球在一次大規(guī)模天體碰撞中形成，距今有44.25億年的歷史。 研究發(fā)表在周一出版的《地球化學(xué)展望通訊》雜志上。 研究的資深作者、芝加哥菲爾德自然歷史博物館羅伯特?普利茲克流星學(xué)和極地研究館館長菲利普?赫克在一份聲明中說：“這些晶體在撞擊后形成，是已知最古老的固體。知道這些晶體的年齡，也就錨定了月球的年齡。” 太陽系早期是混亂的，那時候地球逐漸形成、變大，巖石天體經(jīng)常在太空中碰撞。研究人員說，40多億年前的那段時間里，一個火星大小的天體撞上了地球，甩出一大塊巖石，成了月球。科學(xué)家們一直在努力確定這一關(guān)鍵事件的準(zhǔn)確日期。 火星大小的天體撞擊地球產(chǎn)生的能量熔化了月球表面的巖石。 赫克說：“月球表面巖石熔化時，鋯石晶體不可能形成并保存下來。因此，月球表面的任何晶體一定是在月球的巖漿海冷卻后形成的。” 赫克也是菲爾德博物館尼高尼綜合研究中心高級主任以及芝加哥大學(xué)地球物理系教授。 報告作者稱，這項研究標(biāo)志著首次使用原子探針層析成像法對晶體進行年代測定，在伊利諾伊州埃文斯頓的西北大學(xué)完成。 分析結(jié)果揭曉了鋯石晶體中有多少鈾原子經(jīng)歷了放射性衰變。元素的原子中如果含有不穩(wěn)定的質(zhì)子和中子構(gòu)型，就會發(fā)生變化，其中一些原子會衰變，比如鈾會衰變成鉛。通過比對這一過程所需的時間，科學(xué)家可以通過測定鈾原子和鉛原子的比例來確定某物的年齡。 研究小組利用月壤樣本中的鉛同位素確定了晶體的年齡為44.6億年，這表明月球的年齡至少也是 44.6 億年。 (Translated by Debra) | 