Working out climate change using oxygen isotopes

  We are told that in the past the planet's atmosphere has been colder and warmer than it is today but how do scientists actually know this?   A variety of methods are used but one uses some straight forward (to understand - not necessarily carry out) chemistry. Oxygen has two stable isotopes, 16O and 18O. 16O evaporates faster than 18O so seawater will contain more 18O than 16O due to evaporation. The water will eventually make its way into rivers and back into the ...