How long have diatoms been around?
100 million years ago (mya), it was the Age of Dinosaurs — well before the earliest human ancestors stood erect, at 3.5 mya. The continents were still united in giant land masses. Most divisions of the algae and other broad plant and animal categories were already well established. This is the period when the oldest diatom tests are found. But there might be reason to think diatoms are older than anyone can prove right now, or will ever be able to prove.
