The earth is about 4.6 billion years old, but the oldest ocean floor is only about 200 million years. how do you explain this?

Because they are renewed

Explanation:

Oceanic crusts are usually renewed in the Earth's mantle relatively quickly in subduction zones (where tectonic plates collide with each other) due to their high density, and are less than 200 million years old.

answer; i believe the correct answer is ; large pieces of pangaea drifted in different directions over millions of years;