Microfossils are the microscopic remains of ancient plants and animals, and particularly the plankton, which have inhabited Earth for over one billion years. These fossils tell us about the history of life, the ocean and climate on Earth, and, also, the age of the rocks in which they are found.
Though extremely small, calcareous nannoplankton are so abundant that they: 1) are visible from space as bright swirling blooms in the surface oceans, 2) form much of the calcareous ooze sediments that cover the modern ocean floors, and 3) make up the bulk of chalk and limestone rocks, such as the white chalk cliffs and downs of England. As well as the inherent beauty of the fossils and living coccoliths and coccospheres, they are of great scientific importance for a number of reasons, which include:
- quickly and easily providing the age of the rocks in which they occur; Biostratigraphic Age Dating
- giving information about the environment in which they lived, e.g., water temperature, amount of nutrients/food, etc; Environmental Indicators
- providing information about rates and trends of evolution, and the links between evolution and environmental change; Rates and trends of evolution
- providing information about the operation of global biogeochemical cycles, such as the carbon and sulphur cycles; and Nannoplankton and biogeochemical cycles
- Planktonic foraminifera
Planktonic foraminifera are calcareous zooplankton that live in the surface waters of the ocean. The fossil shells (tests) are generally less than 0.5 mm in size and leave a long and valuable fossil record that we can exploit to document changes in the temperature and productivity of the oceans through time (mainly Cretaceous and Cenozoic).
These organisms are phytoplanktonic algae (i.e., photosynthesising, floating and single-celled) and lie at the base of the ocean food chain, much as plants do on land. Descendants of these fossils still live in the oceans today and the dominant group is called the coccolithophores, a subgroup of the haptophyte algae. The fossil record contains many examples of these protective plates, called coccoliths, and even complete spheres, known as coccospheres. The strong similarity with modern coccoliths means we are confident that these fossils were produced by ancestors of modern coccolithophores (see images of Emiliania huxleyi and Watznaueria britannica, above), but there are also extinct types with weird and wonderful architectures that may or may not have been closely related to the modern forms (see images of Schizosphaerella and Rhomboaster above).