O. A. Schaeffer

Gas Analysis of the Lunar Surface

The rare gas analysis of the lunar surface has lead to important conclusions concerning the moon. The large amounts of rare gases found in the lunar soil and breccia indicate that the solar atmosphere is trapped in the lunar soil as no other source of such large amounts of gas is known. The cosmogenic products indicate that the exposure ages of the 17 lunar rocks measured vary from 20 to 400 million years with some grouping of the ages. The most striking feature is the old potassium-argon age which for the 14 rocks analyzed varies from 2.5 to 3.8 billion years. It is concluded that Mare Tranquillitatis crystallized about 4 billion years ago from a molten state produced by a large meteorite impact or volcanic flow.

Effect of ocean dumping on 13C/12C ratios in marine sediments from the New York Bight

In order to evaluate the influence of the ocean dumping of sewage sludge upon the organic carbon fraction of sediments of the New York Bight, a study of carbon isotopic variations in surface sediments from the area has been completed. On the basis of our 13C/12C measurements, it appears that: (1) sewage is depleted in 13C as compared to average marine organic sedimentary carbon, and (2) δ13C values from sediments of the New York Bight show systematic variations which are a direct consequence of the sludge disposal. Based on assumptions regarding inputs of sedimentary carbon to the sea floor in this area, we have modeled these 13C/12C variations in terms of progressive dilution of normal marine carbon with carbon derived from the ocean dumping of wastewater sludges. The isotopic composition of carbon in sediments from the New York Bight may serve as a quantitative tracer of sewage sludge components.

Lunar volcanism - Age of the glass in the Apollo 17 orange soil.

The formation age of the glass in the orange soil brought back by the Apollo 17 astronauts from the Taurus-Littrow valley has been measured by the 40Ar-39Ar stepwise heating technique to be 3710 � 60 x 106 years. The orange glass is thus much older than expected. Four fragments, presumably from the subfloor basalt, were also analyzed and have crystallization ages of 3710 � 70, 3720 � 50, 3770 � 50, and 3790 � 70 x 106 years. These ages do not provide evidence for recent extensive lunar volcanism. The magmatic activity in the Sea of Serenity and the Sea of Tranquillity occurred very close in time, if not contemporaneously. The volcanic activity in the Sea of Tranquillity and the Sea of Serenity may have been triggered by the impact event forming the Sea of Rains basin.

Age of a lunar anorthosite.

The crystallization age of an Apollo 15 anorthosite rock, 15415,9, returned from the lunar highlands has been measured to be (4.09 � 0.19) x 109 years. The primitive lunar crust must have been formed in the first 300 to 400 x 106 years. The results give some credence to the hypothesis that the primitive lunar surface was molten and large-scale fractional crystallization occurred in the early history of the moon.

Ages of Crystalline Rocks from Fra Mauro

Crystallization ages for six rocks from Fra Mauro have been measured by the argon-40-argon-39 method. All six rocks give an age of 3.77 � 0.15 x 109 years, which is the same as for fragmental rocks from this site. It is concluded that the Imbrium event and the crystallization of a significant portion of the pre-Imbrian basalts were essentially contemporaneous.

Potassium: Argon Dating of Iron Meteorites

The potassium:argon age of the metal phase of Weekeroo Station iron meteorite, determined by neutronactivation analysis, is about 1010 years; it is similar to ages previously measured for other iron meteorites, but distinctly disagrees with a strontium: rubidium age of 4.7 X 109 years measured by other workers on silicate inclusions in this meteorite.

40Ar/39Ar ages from Fra Mauro

Abstract High temperature 40 Ar/ 39 Ar ages have been determined for four rock fragments selected from coarse fines returned from Fra Mauro. Three are fragmental rocks in varying stages of recrystallization and the fourth is crystalline with a gabbro mineralogy, relatively devoid of shock features. All of the fragments have a common age of 3.75 ± 0.15 × 10 9 yr. The ages suggest intense activity, possibly the Imbrium event, at 3.75 × 10 9 yr ago which has precluded the identification of more primitive material.

37Ar and 39Ar in meteorites and the spatial cosmic ray gradient

Cosmic-ray-produced 37 Ar ( t 1/2 = 35 days), and 39 Ar ( t 1/2 = 269 years) in the Fe-Ni phase of meteorites have been studied in connection with their implications for the radial gradient of cosmic ray particles. For the chondrite, Can˜on City, which fell on October 27, 1973, we found 20.1 ± 1.5dpm/kg FeNi of 37 Ar and 22.5 ± 1.4dpm/kg FeNi of 39 Ar. Usually, the 37 Ar/ 39 Ar ratio is used to deduce a spatial gradient. However, 37 Ar data reported in the literature are inconsistent. They fluctuate much more than could be accounted for by different orbits and the anticipated correlation with the cosmic ray neutron registrations is rather weak. Consequently, the 37 Ar/ 39 Ar-derived gradient has a low confidence level. On the other hand, 39 Ar activities group close to a mean value of 22.5 dpm/kg FeNi and appear to be almost independent of the different meteoroid orbits. A comparison of measured 39 Ar activities in meteorites with those calculated for orbits obtained from fireball data shows that a gradient of 10%/Au or less is reconcilable with the experimental findings. The average gradient ( E > 200MeV) during the last 500 years was probably not much larger than that measured presently by the Pioneer 10 and 11, and Helios spacecrafts.

The duration of volcanism in Mare Serenitatis

Abstract The crystallization ages of a suite of Apollo 17 basalts from four different stations have been measured using the 39 Ar- 40 Ar stepwise heating technique. The rocks analyzed include all principal petrographic types found at Apollo 17 landing site. A correlation between the ages and the petrographic type exists; plagioclase-poikilitic ilmenite basalts are youngest and olivine porphyritic ilmenite basalts are the oldest. The duration of volcanism in Mare Serenitatis is about 200 m.y., the same as observed for Mare Imbrium, and less than observed for Mare Tranquillitatis, 400 m.y. A relationship between duration of volcanism and gravity anomalies is noted. The cosmic ray exposure ages (in m.y.) for various locations range as: station 4, 58–315; station 5, 85–440; station 6, 110; station 8, 90–160.