Spaceprobes from three countries are currently orbiting the Moon, and there are plans to send robotic rovers back to our nearest neighbor. A recent paper in Proceedings of the National Academy of Sciences, co-authored by UC Davis geologist Qing-zhu Yin, sets out some things to do when they get there — ways that lunar soils could tell us about the early history of the Earth.

The Earth/Moon system formed about 4.5 billion years ago, but there is very little geological record of the Earth’s surface beyond 4 billion years ago. But recent studies show that the Moon may have been much closer to the Earth — about half the distance it is now — at that time, and that it has kept its near side turned to Earth throughout. So it’s possible that elements from the Earth’s atmosphere have found their way to the Moon’s surface, leaving a record in the lunar soil.

Examining lunar soils for light elements such as helium, oxygen, nitrogen, neon and argon could help planetary scientists understand this early stage in the formation of our planet, according to Yin and co-authors Minoru Ozima and Yayoi Miura of the University of Tokyo and Frank Podosek of Washington University in St. Louis.

Major questions include:

1. When did the Earth’s magnetic field develop?
2. When did Earth develop an oxygen atmosphere — a sign of the emergence of life?
3. How was the Earth/Moon system changed over billions of years; for example, did Earth’s days used to be a different length?

Concluding, the authors write that “sampling of lunar soils from both the near and far side is also within current technology.” In fact, an Indian space probe just joined spacecraft from Japan and China in orbit around the Moon. None of the current missions will land a robot on the moon, although the Indian probe will drop an “impactor” on the Moon’s surface. However, Google Inc. is funding a $30 million prize for a private effort to put a roving robot on the Moon, and China plans to land a rover on the Moon by 2012.