Calcareous nannofossils are the remains of single-celled algae that first emerged in ocean environments around 200 million years ago.
Nannofossils preserve planktonic organisms that are widely distributed throughout the world's oceans.
The organisms secrete tiny platelets on their surface, which are constantly replaced during their life cycle. It is these platelets, made of calcium carbonate (calcite), that are preserved as fossils in marine sediments.
One of the most recognised groups of nannofossils are the coccoliths: single disc-like platelets produced by organisms known as coccolithophores. Occasionally complete coccospheres (amalgamations of coccoliths) are preserved.
Over many millions of years these calcite deposits become limestone.
The size and relative abundance of calcareous nannofossils in the world's oceans makes them important tools for:
Their microscopic size (c 10µm) means a large number of complete coccoliths or platelets can be obtained from only a tiny amount of sediment.
Learn more about nannofossils and how they can be used to reconstruct ancient climates.