Asphalt seems hard enough when you fall on it, but the truth is that nothing more than the lightly falling rays of the sun are required to damage asphalt. For as the sun bakes out residual moisture from the tar, asphalt becomes brittle and prone to cracking. Thus, in order to keep your asphalt viable you need to be on the lookout for signs of damage, so you can take steps to make repairs and prolong the life of your parking lot.
New asphalt should be a deep, matte black color. While dirt that collects on the tar will make it appear a dirty brown color, the sun will also cause the color of the asphalt to fade. As the sun bakes more and more residual color out of the asphalt, it will fade to a dull grey color at which point, your asphalt will loose the ability to flex with the pressures placed upon it. Instead of flexing, brittle, grey asphalt will crack under pressure. You should treat your asphalt with a sealcoat right after installation to help retain asphalt tar retain moisture, and you should retreat with a seal coat whenever you see the color of your pavement start fading to grey.
Cars can leak oil, gas, or other liquids that can act as solvents to break down the tar that holds your pavement together. Once the tar is no longer strong enough to hold the pebbles that make up the pavement in place, potholes will begin to form. First, you should properly patch potholes before treating with a sealcoat, which will help to protect the underlying asphalt from solvents by keeping them on the surface.
As cracks start to form as the result of pressure on brittle pavement, water can widen cracks through the process of frost wedging. If left unchecked, these cracks will spiderweb through pavement until you are left with alligator cracks, named because they look like the deep scales on an alligator's back. At this point your pavement is so compromised that nothing is left but replacement. Thus, you should have cracks filled as soon as they start to appear and treat your asphalt with a sealcoat, which will help your pavement shed water and thus prevent further cracking due to frost wedging.
Because the repairs described above are less expensive than replacing your parking lot and will help to extend the life of your pavement, it is in your best interest to inspect your parking lot regularly and make repairs as necessary.