Rock samples from moon

Background How do scientists identify unknowns What about an unidentified rock sample from the moon, for example Scientists compare the moon rock s properties with those of known rocks on earth. By seeking correlations—and ideally, a match—scientists can determine the moon rock s composition. In this lesson, students follow a similar process to discover the Identities of their five chemical unknowns. They compare the data they have collected through observing and testing the unknowns (contained in their test summary tables from Lesson 11) with data from a reliable source of information (contained in Record Sheet 12-A Chemical Information Sheet). 

Meteorite specimens that land on the East Antarctic ice sheet are transported to the margins of the ice sheet and may be exposed on the bare-ice fields in the zone of ablation adjacent to the Transantarctic Mountains, and at the Yamato and Grove mountains of East Antarctica. In addition, several dozen rock samples from the Moon and from Mars have been collected in Antarctica. 

The first moon explorers brought back rock samples of a nature never before seen on earth, but they did not find any new elements. The moon rocks merely added to the proof that the moon, the earth, and the whole universe are made from the same elemental building blocks. 

If you know the half-lives of uranium isotopes and the percentage of lead isotopes in some uranium-bearing rock, you can calculate the date the rock was formed. Rocks dated in this way have been found to be as much as 3.7 billion years old. Samples from the moon have been dated at 4.2 billion years, which is close to the estimated age of our solar system 4.6 billion years. 

No rock samples have been collected from Mercury and Venus, and the arsenic chemistry of their crusts is unknown. Like the Moon, the crustal rocks on Mercury, Venus, and Mars are primarily basalts and other mafic rocks. If the trace element chemistry of their basalts is similar to lunar specimens, they should contain <1 mg kg-1 of arsenic. 

Different evolutionary histories of other terrestrial planets have influenced the relative concentrations of the transition elements compared to their cosmic abundances, as suggested by geochemical data for surface rocks on the Moon, Mars and Venus (Appendix 1). Chemical analyses of lunar samples returned from the Apollo and Luna missions show that minerals and glasses occurring on the Moon contain high concentrations of Fe and Ti existing as oxidation states Fe(II), Ti(III) and Ti(IV). Some lunar minerals, notably olivine and opaque oxides, also contain significant amounts of Cr(H), Cr(III) and Mn(H). The lack of an atmosphere on the Moon simplifies interpretation of remote-sensed reflectance spectra of its surface. 

With the exception of these small amounts of meteoritic matter, the lunar soil is derived from igneous rocks disrupted by impacts and gradually reduced to fine-grained dust. On all landing sites, the soil is much more abundant than rocks or breccias. Except on steep slopes, the whole Moon is covered with a layer dust of at least 5 m thick. The rock samples brought back are separate fragments embedded in the soil once part of the underlying bedrock, they were excavated by the impact of meteorites. 

The values for the Al/Si ratio of the regolith in mare areas, as determined from moon samples as well as via the x-ray fluorescence technique, also differ from the values found in the rock samples of mare basalts (Tables 2 and 3), the latter being somewhat lower. These differences can be explained by the admixture of anorthositic material from the lunar highlands, as found at the... 

Another direct consequence of the Moon s comparatively small size was early, rapid decay of its internal heat engine. But the Moon s thermal disadvantage has resulted in one great advantage for planetology. Lunar surface terrains, and many of the rock samples acquired from them, retain for... 

Low energy cosmic rays entering the solar system are convected away from the Sun by the solar wind. At lower energies solar flares contribute most of the particles, which tend to mask the galactic contribution. During periods of maximum sunspot activity, solar flares sporadically contaminate the solar system with these low energy particles. The tracks and induced radioactivity that these particles have been found to produce just below the surface of samples of Moon rock, indicate that flares have been a... 

The analysis of real samples, such as the soil and rock samples brought back to the earth from the moon by the Apollo astronauts, is usually quite complex compared with the analysis of materials studied in laboratory courses. As discussed in this chapter, the choice of analytical method for real materials is not simple, often requiring consultation of the literature, modification of existing methods, and extensive testing to determine method validity. 

The Earth and the Moon were formed just over 4.5 billion years ago. The age of the craters on the Moon, dated from rock samples brought back by the Apollo astronauts, suggests that our planetary system was bombarded by meteorites for at least 500 million years. The bombardment ended around 3.8 to 4 billion years ago. The oldest sedimentary rocks on Earth, which were laid down along what is now the west coast of Greenland, have been reliably dated to an age of 3.85 billion years — a mere 700 million years after the formation of the Earth and certainly not long after the end of the bombardment. 

Noble gas studies have been done on well-documented samples from two very different solar system bodies, the Earth and Moon. There is one other planet. Mars, from which we have samples, but those samples are nearly 20 (at the start of 2002) Martian meteorites, rocks from unknown locales on Mars. Even from those, though, we have learned enough to realize that Mars is a fascinating compromise between the Earth and Moon. 

The amount of sample taken must be sufficient for all analyses to be carried out in duplicate or triplicate, if possible. Of course, if only a small quantity of sample is available, as may be the case for forensic samples from a crime scene or rocks brought back from the moon, the analyst must do the best job possible with what is provided. 

Fig. 18. 23 This small rock sample was collected on January 18, 1982 by Ian WhiUans and John Schutt on the Middle-Western ice field on the East Antarctic ice sheet west of the Allan HiUs. It was subsequently identified as a lunar rock by scientists at the Johnson Space Center in Houston, Texas, and was assigned the identifying number ALHA 81005. The rock contains fragments of coarse-grained plagioclase feldspar in a fine-grained black matrix and has been described as an anorthosite breccia from the highlands of the Moon. (Courtesy ofNASA/LPI))...

Appendix 18.12.3 recovered in Antarctica (Zeigler et al. 2005). Several specimens are paired because they are either fragments of a lunar rock sample that broke up during its passage through the atmosphere or because they originated from the same impact crater on the Moon (i.e., source pairing, Warren 2005). 

Samples that are 4.6 X 10 years old have been found in meteorites. This is the best present estimate for the age of the solar system. Example illustrates this type of calculation for rock from the Earth s moon. 

The moon rocks brought back to earth are only a tiny sample of the moon s surface, but they are enough to show that some elements common on earth may be rare on the moon, and some that are rare here on earth may be common on the moon. So far, as on earth, oxygen and silicon seem to be the most common lunar elements. Early experiments have found more uranium and less potassium, more titanium and less sodium. Oxygen is strikingly absent from some minerals, but natural glass is far more common than it is on earth. The rare, noble gases are fairly abundant, trapped in little bubbles in the rocks. 

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