On the Moon as it was on Earth

Abstract

Does the Moon's surface contain an archive of the early history of Earth? According to an intriguing idea, based on recently published analyses of lunar soils, it might do — and the proposal can be tested. The Moon as a whole is strongly depleted in volatile elements, but lunar soils contain large amounts of nitrogen and noble gases. The conventional explanation is that these elements derive from solar wind hitting the lunar surface. Now a decidedly unconventional suggestion has been made: what if nitrogen and noble gases originating on Earth also found their way to the Moon? The escape of atmospheric constituents is prevented today by the Earth's geomagnetic field. But the nitrogen isotope ratio in lunar soils cannot be explained by the accumulation of solar material alone: it is possible that substantial amounts of nitrogen and light noble gases could gave been transported from Earth's ancient atmosphere before the geomagnetic field developed. This proposal can be tested by comparing implanted materials in soils from near and far sides of the Moon. If a difference is found, another mystery might be solved: the age of Earth's geomagnetic field.