The Geologic temperature record are changes in Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's environment

Environment (biophysical)

The biophysical environment is the combined modeling of the physical environment and the biological life forms within the environment, and includes all variables, parameters as well as conditions and modes inside the Earth's biosphere. The biophysical environment can be divided into two categories:...

 as determined from geologic

Geology

Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

 evidence on multi-million to billion (10⁹) year time scales. The study of past temperatures provides an important paleoenvironmental insight because it is a crucial component of the climate and oceanography of the time.
Our evidence for past temperatures comes mainly from isotopic considerations (especially ); the Mg/Ca ratio of foram tests, and alkenone

Alkenone

Alkenones are highly resistant organic compounds produced by phytoplankton of the class Prymnesiophyceae.The exact function of the alkenones remains under debate....

s, are also useful.