Mega year ago
The Mega year ago, often abbreviated as Ma or Mya, is a useful shorthand notation for long times that is more concise than scientific notation. One Ma is equal to one million years. In evolutionist and secular accounts of the development of the earth, the time for geological events such as the formation of a mountain to unfold is typically on the order of a few Ma.
Instead of "atheists claim that trilobites went extinct 251 million years ago", one would write "atheists claim that trilobites went extinct 251 Ma". The use of "Ma" allows one to avoid word repetition when writing.