PHASE 2: Cratering
The moons surface is so old, it serves as a record of the immense bombardment occurring 4 billion yrs ago, not just with innumerable craters, but it's surface rock is fractured to a depth of several km! Several of the mare are actually old, very large impact craters which have since filled with lava. Mare Imbrium was created 3.8 billion years ago by an asteroidal body tens of km in diameter, throwing out immense amounts of ejecta to form the mountains ringing the basin. It was along these southern mountains that Apollo 15 landed. Exactly opposite the largest craters on the moons surface, we see jumbled terrain, created by the impacts shock wave as it traveled through and around the moon.

PHASE 3: Flooding
The surface rock had long since solidified, and was now riddled with craters, but below the crust the mantle was still molten. Large impacts cracked the crust, resulting in lava flows in the low lying regions. Many areas show evidence for multiple flows, spread out over a billion years. Curiously, the far side of the moon looks quite different than the side we always see. It shows few maria. The crust is thicker on the far side, keeping the molten mantle from seeping through even when large impacts have hit the moon there.

PHASE 4: Surface Evolution
Without active geology, water or wind, the surface evolution of the moon has been minimal.

How did we get such a big moon?
Fission. The moon spun off the Earth after Earth had already been partially differentiated (making the Moon low density). However the moons orbit is not aligned with Earth's equator.
Co-accretion. The moon and Earth formed as a binary. But this does not explain their differing chemical composition (little Fe in the Moon, though they do have similar ratios of light elements).
Capture The moon was later captured by Earth. This requires forming the Moon else where (near the Sun to get the right composition). The Earth could not easily capture something this massive.

Large-Impact Hypothesis
At the time Earth formed 4.5 billion years ago, other smaller planetary bodies were also growing. One of these hit earth late in Earth's growth process, blowing out rocky debris. A fraction of that debris went into orbit around the Earth and aggregated into the moon. This theory explains the Moon chemistry very well, if the collision occurred after the Earth had differentiated and moon volatiles (water) were lost to space.