Today I learnt in college that marine sediments can be used to reconstruct the climate up to 500 million years back. I find that number very strange because in another class we learnt that the ocean floor "recycles" every few million years as a result of plate tectonics, and that the oldest ocean floor is 200 million years old.
I asked the lecturer about this, but he said he did not know. So I was hoping anyone here could tell me how many years old the climate we can recover through marine sediment cores is and why.