TOEFL Listening: ETS-TOEFL听力机经 - 3E13899CSRW2WW13P$

What is the main purpose of the lecture? A. To explain how geologists determine the dates of ice ages B. To compare the geologic features of several different ice ages C. To discuss the possibility of a severe ice age during the Cryogenian period D. To examine the effects of a Cryogenian ice age on subsequent climate patterns