♪ The Earth BEGAN to cool
The Big Bang Theory Season 7, Episode 7
♪ The autotrophs BEGAN to drool,
Neanderthals developed tools ♪
The Big Bang Theory Season 5, Episode 14
♪ The Earth BEGAN to cool
The Big Bang Theory Season 7, Episode 13
# The Earth BEGAN to cool #
The Big Bang Theory Season 11, Episode 12
♪ The Earth BEGAN to cool
The Big Bang Theory Season 12, Episode 21