Clicker q. 1: when it mixes, temperatures are close to each other. Cold lake will have the waters closer together in the summer. Make sure we can answer these questions or be able to draw them. High degree of water evaporation taking o16 out of the ocean an putting it in the ice. O16 is preferentially taken out during evaporation can tell you how much ice there is in the world. May have been more prior to this, but many not be found in the fossil record. Fossil levels very distinct from each other because if most of life went extinct, what survived would have plenty of resources to grow and proliferate undergo adaptive radiation. Adaptive radiation there is an ecological opportunity that organism can undertake to diversify and use all those resources. After mass extinctions there is massive speciation events for this reason. More ice on land the less water you have in the oceans.