The Earth's geology is very active. It is effectively a 4.6 billion year old "rock blender" that has recycled its surface material to the point that no rocks exist on Earth's surface that can be dated back to the time of its formation. In addition, the Earth has an atmosphere, which erodes the surface via wind (carrying sand and debris) and precipitation (rain, snow, etc.). The surface of Earth is constantly being changed, so material that we gather on Earth's surface cannot be used to directly date the age of our planet or our solar system (except for meteorites, but they are from somewhere else). Using radiometric dating techniques on some surface rocks and components of others, geologists reassure us that the Earth is at least 2-3 billion years old. However, is that really the age of the solar system, or even the Earth, for that matter?
             No, the Moon is a much better place to look for clues as to the age of both our planet and our solar system. But why?
             Firstly, the Moon is small. So small that it cooled off efficiently and very early after its formation, thus "freezing" its geology at a very young age. Some lunar surface material is doubtlessly from the earliest days of its existence. On top of this, the Moon has no atmosphere. No wind and no running water exist there to erode away and change its surface material. The only force of erosion on the Moon is constant meteoric bombardment from space. Micrometeorites (speedy little meteorites no bigger than sand grains) slam into its surface by the trillions every day, creating the powdery regolith that covers the Moon's surface.
             However, in the highlands particularly, very ancient rocks (4.6 billion years old) are abundant. These areas are heavily cratered, many of which are overlapping (which indicates that some craters are older than others). Counting the number of craters per area in these regions gives us a very good idea of the rate o
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