evidence: But some of the most common climate proxies at this timescale are even more miniscule. Foraminifera (known as "forams") and diatoms are unicellular beings that tend to live on the ocean seafloor, and are often no bigger than the period at the end of this sentence. Because they are scattered all across the Earth and have been around since the Jurassic, they’ve left a robust fossil record for scientists to probe past temperatures. Using oxygen isotopes in their shells, we can reconstruct ocean temperatures going back more than 100 million years ago. [...] But when we’ve gone back so far that there are no longer even any conodont teeth, we’ve lost our main indicator. Past that we have to rely on the distribution of sediments, and markers of past glaciers, which we can extrapolate out to roughly indicate climate patterns. So the further back we go, the fewer proxies we have, and the less granular our understanding becomes. "It just gets foggier and foggier," says Brian Huber, a Smithsonian paleobiologist who helped organize the symposium along with fellow paleobiologist research scientist and curator Scott Wing.