Why have questions about mantle convection been so difficult for scientists to answer lately?

chinese civil war took place over a long period of time between 1927 and 1950. the war was interrupted when japan invaded china in 1936 and by world war ii. the war was fought between the nationalist government of china, also called the kuomintang (kmt), and the communist party of china (cpc). 

most glaciers are found in mountainous areas near the equator. is the answer you're look for.