New research suggests that what was previously considered to be the oldest life on Earth cannot be the oldest life on Earth:
The argument over whether an outcrop of rock in South West Greenland contains the earliest known traces of life on Earth has been reignited, in a study published in the Journal of the Geological Society. The research, led by Martin J. Whitehouse at the Swedish Museum of Natural History, argues that the controversial rocks “cannot host evidence of Earth’s oldest life,” reopening the debate over where the oldest traces of life are located.
Scientists had dated the rocks originally at 3.85 billion years old, older than any other life we knew of. But the new research challenges the original dating, finding no evidence that they are any older than c. 3.67 billion years.
Obviously this puts John McCain back in the running as the possible oldest life on Earth.