Final answer:
The average rate of sea floor spreading is about 5 centimeters per year, resulting in the creation of about 2 square kilometers of new oceanic crust annually. This rate allows for the renewal of the entire oceanic crust in about 100 million years.
Step-by-step explanation:
The average rate of sea floor spreading refers to how quickly new oceanic crust is formed and spreads apart at mid-ocean ridges. According to the given information, there are about 60,000 kilometers of active rifts with an average separation rate of about 5 centimeters per year. This means that each year, about 2 square kilometers of new ocean crust is created.
This rate of spreading is enough to renew the entire oceanic crust in about 100 million years. Given that the age of the Earth is much older, about 4.5 billion years, the present ocean basins are considered relatively young features on our planet.