Answer:
Option C, 55 million years ago
Step-by-step explanation:
It was during the Late Paleocene Thermal Maximum (LPTM) when the earth became extremely hot. This period occurred some 55 million years ago. During LPTM, the temperature of the earth rose by some five to eight degree Celsius over and above the normal temperature during the summer season. This temperature change occurred during the epoch of Paleocene and Ecocene.
Hence, option C is correct.