Great questions! The only organisms on the planet known to make alkenones are members of the class of algae Haptophyta. To make things even more confusing, not all members of the Haptophyta produce alkenones!

The algae grow in the water of the lake, but when they die they settle out onto the lake floor where their cells, including their alkenones and their DNA (two of the things we’ve been looking for), get piled up over time like a layer cake. Take a look at my dispatch called “Coring in Greenland & NYC” for an example of how we obtain long core records from the bottoms of lakes. Your analogy to dinosaur fossils is right on… the deeper in the lake sediment you go, the older the material you find and you can use it to reconstruct the environmental and climate history of the region.

Thanks for the questions!