When they have a core of deep sea sediments , the scientists have to make an age determination.
How might they determine sample’s age?
There are a lot of microfossils in oceanic sediments and they provide a basis for age determination. The paleontologists studying sedimentary sequences have established first appearences and extinction of species through time.
Microfossils species in marine sediments are unique to a geologic epoch making them very useful for age determination.
Here Foraminifera and Coccolithophores are the “superstars” of the oceanic fossils . They are abundant , very diversified and widespread. They provide evidence of the relative ages of sediments (http://www.ucmp.berkeley.edu/fosrec/Wetmore.html) (http://www.ucl.ac.uk/earth-sciences/research/micropal/research/nannoplankton-information/coccolithophores).
Plus the chemistry of their shells reflects the chemistry of the water in which they grew up. And it is helpful to describe the past climates and understand how climates and ocean’s currents have changed in the past… to understand the future too!