As well as being a palaeoclimatologist I'm an organic geochemist – it's a bit of a mouthful, but an organic geochemist studies molecular fossils, natural compounds , molecules of all types. And so we study compounds or molecules that are produced by organisms.
What's useful about these is that in some situations you may have ocean or lake sediments and the organisms that were living at the time the sediment was deposited have completely decayed.
So there are no large fossils that can easily be looked at or even microfossils that can be seen through a microscope.
But what are preserved are particular compounds and some compounds , especially lipids or fat-type compounds which are not soluble in water, can be preserved in sediments even after the body of the organism has decayed.
So this is like the geological equivalent of forensic science. We are
looking at things at the molecular level.