Genesis skirt

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The lunar sample 15415 - better known as Genesis Rock (German Genesis stone ) - is a rock sample from the moon that was picked up in 1971 by astronaut David Randolph Scott during the Apollo 15 mission during the second space mission (EVA 2). It was given the nickname Genesis in allusion to the Book of Genesis and the story of creation, because the sample was hoped to provide information about the origin of the moon. This from the ancient highlands crust coming lunar rock is now in the Lunar Sample Laboratory Facility in Houston kept.

composition

The Genesis stone

Geochemical analyzes of the 269.4 gram Genesis stone show that it is an iron-containing anorthosite , which is mainly composed of plagioclase ( anorthite ). It was initially believed to have been formed during the formation of the solar system 4.5 billion years ago. It was found in Spur Crater , a moon crater , next to similar stones.

Petrography and Mineralogy

Replica of the Genesis Rock in the Astronaut Hall of Fame

The Genesis Rock consists of 98% plagioclase, in which diopside pyroxene ( Augite ) are enclosed. Orthopyroxene , ilmenite , spinel , olivine , apatite and silicic acid occur in traces . The plagioclase are very rich in anorthite (An 96-97 ), their maximum grain size varies between 18 and 30 millimeters. The plagioclase show gently rounded grain boundaries and triple points where the crystals touch at an angle of 120 °, characteristic of a metamorphic embossed structure . The tiny diopside Augites (grain size around 0.1 millimeters) not only form inclusions, but also polygons at grain boundaries and septa between large plagioclases. The pyroxenes show separation between pigeonite and orthopyroxene. The latter can also appear as isolated grains, the crystal structure of which suggests heating to 500 to 600 ° C for the last time.

The plagioclase are not zoned and contain only small amounts of MgO and FeO. Twinning was carried out according to the laws of albite and pericling. Some areas are cataclastically deformed, mild shock effects can be recognized by offsets on the polysynthetic twin lamellae.

The majority of the pyroxenes are calcium- rich, diopside augites of the formula Wo 46 En 39 Fs 16 . They contain thin hypersthene lamellae and hypersthene areas with the formula Wo 2.5 En 58 Fs 39.5 (low in calcium). There are traces of ilmenite on the outside of the pyroxe grains.

Based on the high anorthite content of the plagioclase and the relatively iron-rich composition of the calcium-poor pyroxene, the Genesis Rock can be classified as an iron-rich anorthosite .

Chemism

The following table gives geochemical analysis values ​​for the Genesis Rock and its plagioclase:

oxide Rock
(wt.%)		 Plagioclase
(wt.%)		 Trace
element		 Rock
(ppm)		 Plagioclase
(ppm)
SiO 2 44.93 43.20-44.80 Sc 0.4-0.437 0.12-0.27
TiO 2 0.016-0.025 0.007-0.009 Cr 19 - 63 1 - 8.5
Al 2 O 3 35.71 34.50-37.00 Co 0.19-0.26 0.012-0.358
FeO 0.199-0.202 0.08-0.16 Sr 172-202 141-246
MgO 0.16-0.53 0.042-0.071 Ba 6 - 6.5 6-22
CaO 20.57-21.00 19.34-20.10 La 0.118-0.210 0.120-0.391
Na 2 O 0.356-0.384 0.22-0.375 Eu 0.805-0.820 0.740-1.290
K 2 O 0.014-0.017 0.01-0.05 Nd 0.175-0.200 0.265

In the case of rare earths , the pronounced, positive europium anomaly is remarkable (twenty times the chondrite value).

Age

While it was originally assumed that the Genesis Rock is to be addressed as the original lunar crustal rock, later age determinations only resulted in 4000 ± 100 million years BP (the argon method yielded ages which varied between 4090 and 3910 million years BP). The rock was therefore younger than the age of formation of the moon (4533 million years BP) and had only formed after the lunar crust had solidified. The Genesis Rock is still a very old rock sample that crystallized during the prenectarian period .

Age determinations on pyroxenes of other anorthosite samples meanwhile use samarium-neodymium dating to infer a crystallization age of 4460 million years BP. This age is around 100 million years younger than when the solar system was formed .

After its formation, the Genesis Rock had been exposed to cosmic radionuclides several times . Overall, based on 38 ares, a residence time of around 100 million years resulted and on the basis of 81 kr 104 million years. It was also found that the handpiece had lost 98% of its 3 He and 40% of its 40 Ar by diffusion .

literature

Web links

Individual evidence

  1. ↑ What is the oldest rock found on the Moon? lroc.sese.asu.edu; APOLLO 15, Lunar Samples by Category ( Memento of the original dated June 12, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. lpi.usra.edu (Retrieved June 18, 2010). @1@ 2Template: Webachiv / IABot / www.lpi.usra.edu
  2. ^ Paul I. Casey: Apollo: A Decade of Achievement . JS Blume Publishing, 2013, p. 201 ( limited preview in Google Book search).
  3. ↑ 15415 Ferroan Anorthosite curator.jsc.nasa.gov, (PDF; 458 kB. Accessed June 18, 2010).
  4. ↑ HT Evans, inter alia: The crystal structure and thermal history of orthopyroxene from lunar anorthosite 15415 . In: Earth Planetary Science Letters . tape 37 , 1978, pp. 476-484 .
  5. ↑ F. Albarede: The recovery of spatial isotopic distributions from stepwise degassing data . In: Earth Planetary Sciences Letters . tape 39 , 1978, p. 387-397 .
  6. ^ MD Norman, LE Borg, LE Nyquist, DD Bogard: Chronology, geochemistry, and petrology of a ferroan noritic anorthosite clast from Descartes breccia 67215: Clues to the age, origin, structure, and impact history of the lunar crust . In: Meteoritics and Planetary Science . tape 38 , 2003, p. 645-661 .
  7. ^ A. Chaikin, T. Hanks: A man on the Moon: the voyages of the Apollo astronauts . Penguin Books, New York, NY 1998.
  8. ↑ O. Eugster, among others: Cosmic ray exposure histories of Apollo 14, Apollo 15 and Apollo 16 rocks . In: J. Geophys. Res. Band 89 , 1984, pp. B498-B512 .