What has the Earth's average surface temperature been for the past 900 000 years? 

A)  fairly steady temperatures until recently 
B)  a steady warming trend 
C)  fairly steady with occasional cool spells 
D)  many fluctuations of several degrees Celsius

The Earth's average surface temperature has fluctuated several degrees Celsius over the past 900,000 years, based on ice core records and other sources of data. These fluctuations have been caused by natural phenomena such as changes in the Earth's orbit, volcanic activity, and variations in the sun's energy output. While there have been periods of relatively steady temperatures, such as during the Holocene epoch (which began around 11,700 years ago), overall the temperature has varied significantly over this time period.