How Do We Know What Earth's Temperature Was Many Years

How do we know what Earth's temperature was many years before thermometers existed?

A) From historical information about the climate recorded by Vikings and other travelers during the ice ages.
B) From laboratory experiments that reconstruct the conditions (the atmosphere and sea level, primarily) of earlier times and then measure the resulting temperature.
C) From computer calculations that start from the conditions (the atmosphere and sea level, primarily) of earlier times and then calculate the resulting temperature.
D) From such indirect methods as tree rings (the thickness and density of a ring is dependent on the temperature at the time of growth) and annual layers of ice in ice cores.
E) From computer calculations that work backward from the present time to calculate the temperature at earlier times.