Chemical analysis of the oxygen isotopes in foraminifera shells allow scientists to create a climate record like the one shown here. the chemical composition of shells depends on the temperature of the surrounding water and the presence or absence of large polar ice sheets.

fossil data like this indicates that

Fossil data acquired by the the chemical study of oxygen isotopes ratio i.e ¹⁶O and ¹⁸O, in the shells of foraminifera, helps in indicating the palaeoclimatic condition as well as the type of food habitat.

  Foraminiferas are unicellular organisms that are comprised of a hard shell which was made of chitin (a fibrous like substance). They are very prone to frequent environmental changes.

Scientist use this organism's hard shell to study about the climatic condition during their time of existence by comparing this oxygen isotopes.