Toward understanding early Earth evolution: prescription for approach from terrestrial noble gas and light element records in lunar soils.

Because of the almost total lack of geological record on the Earth's surface before 4 billion years ago, the history of the Earth during this period is still enigmatic. Here we describe a practical approach to tackle the formidable problems caused by this lack. We propose that examinations of lunar soils for light elements such as He, N, O, Ne, and Ar would shed a new light on this dark age in the Earth's history and resolve three of the most fundamental questions in earth science: the onset time of the geomagnetic field, the appearance of an oxygen atmosphere, and the secular variation of an Earth-Moon dynamical system.

Terrestrial nitrogen and noble gases in lunar soils.

The nitrogen in lunar soils is correlated to the surface and therefore clearly implanted from outside. The straightforward interpretation is that the nitrogen is implanted by the solar wind, but this explanation has difficulties accounting for both the abundance of nitrogen and a variation of the order of 30 per cent in the 15N/14N ratio. Here we propose that most of the nitrogen and some of the other volatile elements in lunar soils may actually have come from the Earth's atmosphere rather than the solar wind.

Gas-retention and cosmic-ray exposure ages of lunar rock 15555.

The last lava flow in the Hadley Rille area of Mare Imbrium, as inferred from an argon-40-argon-39 experiment on a plagioclase separate from the lunar basalt 15555, occurred 3.31+/-0.03x10(9) years ago.

Ages, irradiation history, and chemical composition of lunar rocks from the sea of tranquillity.

The (87)Rb-(87)Sr internal isochrons for five rocks yield an age of 3.65 +/-0.05 x 10(9) years which presumably dates the formation of the Sea of Tranquillity.

Xenon-iodine dating: sharp isochronism in chondrites.

Measurements of the accumulation of Xe(l29) from radioactive decay of extinct 1(129) in meteorites show that the 1(129)/ 1(127) ratio in high-temperature minerals in diverse chondrites was 10(-4) at the time of cooling. The uniformity in the ratio indicates that the minerals cooled simultaneously within 1 or 2 million years.