Answer to Question 1
Like all Terrestrial planets, Earth was subjected to impact cratering during a period of heavy bombardment. However, Earth's active crust explains why Earth contains so few impact craters. The moon is richly cratered, but Earth's surface has only about 150 impact craters. Plate tectonics and erosion have destroyed all but the most recent craters on Earth.
You can see that Earth's geology is dominated by two processes. Heat rising from the interior drives plate tectonics and erosion by water. The Moon has no atmosphere to create weathering and erosion, and it is geologically inactive, hence why impact craters remained throughout its history.
Answer to Question 2
absolute magnitude
period