https://www.smithsonianmag.com/blogs/national-museum-of-natural-history/2018/03/23/heres-how-scientists-reconstruct-earths-past-climates/#:~:text=The%20true%20h

https://www.smithsonianmag.com/blogs/national-museum-of-natural-history/2018/03/23/heres-how-scientists-reconstruct-earths-past-climates/#:~:text=The%20true%20heavyweights%20for%20reconstructing,have%20an%20exquisite%20fossil%20record https://www.smithsonianmag.com/blogs/national-museum-of-natu.... "The true heavyweights for reconstructing ancient seawater temperatures are the microorganisms. Foraminifera, single-celled organisms roughly the size of the period ending this sentence, occur nearly everywhere in the oceans and have an exquisite fossil record."