Oak trees come from acorns. Acorns are nuts produced by oak trees that drop to the ground in early autumn. Although not generally eaten by modern humans, acorns are beloved fare of squirrels and chipmunks.
Oak trees produce massive amounts of acorns to make up for the ones that scavenging creatures eat. The trees generally don't begin producing acorns until they are 20 years old, and acorn production starts to slow down when a tree hits the century mark.
Once an acorn sprouts, it has a long, slow road to becoming an fully fledged oak tree. The seedlings grow an average of 1 to 2 feet per year. Many mature trees reach heights upwards of 150 feet. The average life span of an oak tree is around 200 years, but they can live much longer under the right conditions.