Final answer:
The oldest seafloor is generally less than 200 million years old due to seafloor spreading and the continuous renewal of oceanic crust at mid-ocean ridges.
Step-by-step explanation:
The oldest seafloor is generally less than 200 million years old because of the process of seafloor spreading. The oceanic crust is constantly being renewed at mid-ocean ridges, where new crust is formed as magma rises from the mantle.
The seafloor spreads apart, pushing the older crust away from the ridge and creating new seafloor in the process. This continuous process of seafloor spreading limits the age of the seafloor, making it relatively young compared to the age of the Earth as a whole.