Moon at the end of the Imbrian Period. This image of the Moon combines data obtained using remote-sensing equipment, with geologic and artistic interpretations to show the Moon as it looked 3.3 billion years ago (end of the Imbrian Period). This is part of a sequence showing the Moon as it looked 4 billion years ago (middle of the Imbrian Period, C004/3887) and today (C004/3885). The Imbrian Period was when the Imbrium and Orientale impact basins formed, leading to the newly-formed lava plains (maria) seen here. This work was done by Don E. Wilhelms and Donald E. Davis, and published by the US Geological Survey in 1971.