文章来源:未知 文章作者:enread 发布时间:2014-04-06 08:22 字体: [ ]  进入论坛
An international team of planetary scientists determined1 that the Moon formed nearly 100 million years after the start of the solar system, according to a paper to be published April 3 in Nature. This conclusion is based on measurements from the interior of  Earth combined with computer simulations of the protoplanetary disk from which Earth and other terrestrial planets formed. The team of researchers from France, Germany and the United States simulated the growth of the terrestrial planets (Mercury, Venus, Earth and Mars) from a disk of thousands of planetary building blocks orbiting the Sun. By analyzing2 the growth history of Earth-like planets from 259 simulations, the scientists discovered a relationship between the time Earth was impacted by a Mars-sized object to create the Moon and the amount of material added to Earth after that impact.
Augmenting3 the computer simulation with details on the mass of material added to Earth by accretion4 after the formation of the Moon revealed a relationship that works much like a clock to date the Moon-forming event. This is the first "geologic5 clock" in early solar system history that does not rely on measurements and interpretations6(解释) of the radioactive decay of atomic nuclei7 to determine age.
"We were excited to find a 'clock' for the formation time of the Moon that didn't rely on radiometric dating methods. This correlation8 just jumped out of the simulations and held in each set of old simulations we looked at," says lead author of the Nature article Seth Jacobson of the Observatory9 de la Cote d'Azur in Nice, France.
Published literature provided the estimate for the mass accreted10 by Earth after the Moon-forming impact. Other scientists previously11 demonstrated that the abundance in Earth's mantle12 of highly siderophile elements, which are atomic elements that prefer to be chemically associated with iron, is directly proportional to the mass accreted by Earth after the Moon-forming impact.
From these geochemical measurements, the newly established clock dates the Moon to 95 ±32 million years after the beginning of the solar system. This estimate for the Moon-formation agrees with some interpretations of radioactive dating measurements, but not others. Because the new dating method is an independent and direct measurement of the age of the Moon, it helps to guide which radioactive dating measurements are the most useful for this longstanding problem.
"This result is exciting because in the same simulations that can successfully form Mars in only 2 to 5 million years, we can also form the Moon at 100 million years. These vastly different timescales have been very hard to capture in simulations," says author Dr. Kevin Walsh from the Southwest Research Institute (SwRI) Space Science and Engineering Division.


1 determined duszmP     
  • I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
  • He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。
2 analyzing be408cc8d92ec310bb6260bc127c162b     
v.分析;分析( analyze的现在分词 );分解;解释;对…进行心理分析n.分析
  • Analyzing the date of some socialist countries presents even greater problem s. 分析某些社会主义国家的统计数据,暴露出的问题甚至更大。 来自辞典例句
  • He undoubtedly was not far off the mark in analyzing its predictions. 当然,他对其预测所作的分析倒也八九不离十。 来自辞典例句
3 augmenting f783964437f5ef94b188085a978a7684     
  • My business was now constantly augmenting, and my circumstances growing daily easier. 现在,我的业务不断扩大,我的境况日益安逸。
  • I spent a penitential weekend augmenting the green acceptable. 我临时唯有利用周末在每顶绿帽子上加一点红色上去,以免男性来宾不肯戴上。
4 accretion 5Jnyi     
  • Every culture is an accretion.每一种文化都是长期积淀的结果。
  • An accretion of sediment at the mouth of the river caused serious flooding.河口堆积物的增加导致河水严重泛滥。
5 geologic dg3x9     
  • The Red Sea is a geologic continuation of the valley.红海就是一个峡谷在地质上的继续发展。
  • Delineation of channels is the first step of geologic evaluation.勾划河道的轮廓是地质解译的第一步。
6 interpretations a61815f6fe8955c9d235d4082e30896b     
n.解释( interpretation的名词复数 );表演;演绎;理解
  • This passage is open to a variety of interpretations. 这篇文章可以有各种不同的解释。 来自《简明英汉词典》
  • The involved and abstruse passage makes several interpretations possible. 这段艰涩的文字可以作出好几种解释。 来自《现代汉英综合大词典》
7 nuclei tHCxF     
  • To free electrons, something has to make them whirl fast enough to break away from their nuclei. 为了释放电子,必须使电子高速旋转而足以摆脱原子核的束缚。
  • Energy is released by the fission of atomic nuclei. 能量是由原子核分裂释放出来的。
8 correlation Rogzg     
  • The second group of measurements had a high correlation with the first.第二组测量数据与第一组高度相关。
  • A high correlation exists in America between education and economic position.教育和经济地位在美国有极密切的关系。
9 observatory hRgzP     
  • Guy's house was close to the observatory.盖伊的房子离天文台很近。
  • Officials from Greenwich Observatory have the clock checked twice a day.格林威治天文台的职员们每天对大钟检查两次。
10 accreted 399b7c34ee4fda3884b15ce56138119d     
v.共生( accrete的过去式和过去分词 );合生;使依附;使连接
  • The story accreted emotion. 这个故事使人精神亢奋。 来自互联网
  • Imperial shrimp accreted with sea cucumber. 寄生在海参身上的帝王虾。 来自互联网
11 previously bkzzzC     
  • The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
  • Let me digress for a moment and explain what had happened previously.让我岔开一会儿,解释原先发生了什么。
12 mantle Y7tzs     
  • The earth had donned her mantle of brightest green.大地披上了苍翠欲滴的绿色斗篷。
  • The mountain was covered with a mantle of snow.山上覆盖着一层雪。
TAG标签: moon earth material