Mankind started measuring temperature and rainfall only a hundred years ago or so, with varying degrees of quality until the satellite era. The Earth has been around for much, much longer than a hundred years! What about climate before that? How do we know about climate change on geological time scales? Why is it important? Can that knowledge tell us anything about future climate? In this talk, I will start by giving an introduction to paleoclimatology. Next, I will talk about my specific research which involves using plankton shells and their chemistry to understand about ocean temperature and salinity in the past. Lastly, I will briefly summarize a recent field expedition where I spent two months on the drillship, JOIDES Resolution with 30 other scientists to investigate the history of Indian Monsoon rainfall.