2. how are oxygen isotope ratios and pollen analysis used to make inferences about ancient climates?

This field of science is called Paleoclimatology. It uses residual elements left in nature and analyzes them in order to understand how paleoclimate worked. These residual elements are called proxies. Oxygen isotope ratios and pollen analysis are two of the many proxies paleoclimatologists use.

-Oxygen isotope ratios: the specific oxygen proxy is Oxigen - 18. Since there are shelled organisms (forams and diatoms) that are found in most water environments and which are able to record evidence of pas environmental conditions in their shells, they are very useful to discover how ancient climate was. This evidence is the presence of stable isotopes in these shells. Water molecules evaporate more off the lighter isotopes (Oxigen - 16) which means that if the water temperature was warmer than usual, the shell will be richer in heavy isotopes (Oxigen - 18). Therefore a shell which has more heavy isotopes indicates a warmer climate.

-Pollen Analysis: when paleoclimatologists want to use pollen they take an ice core sample off a glacier or an ice sheet. Each layer of the ice core will correspond to a specific period of time in the history of Earth. Pollen is found in all layers of an ice core and depending on its quantity allows an understanding of which plants existed in that particular period of time and how many of them there were. It also allows paleoclimatologists how rainy and warm the time period was.