Maybe not.


The earliest clear evidence of life on the Earth has been found in the Dresser Formation in Western Australia, indicating that life, indeed, was flourishing as early as 3.5 billion years ago.  In a region of West Greenland, known as the Isua Supracrustal Belt, there are chemical traces within those rocks that might indicate that life existed on the Earth at least at the time these particular rocks formed, about 3.8 billion years ago.  And so life did exist on the Earth at least within the first billion years after the planet had formed.  But did it originate on Earth?


The details of how life originated remain elusive, though the general outline is gradually emerging.  The origin of life is now in the realm of plausible, accessible chemistry and is no longer considered a miraculous or rare event.  But the early Earth with its high temperature and large ocean, which was churned by frequent storms, seems to be too harsh of an environment for complex chemicals, necessary for life, to have formed.  And so life probably began elsewhere, in a place where there was a more benign environment.


Early Mars seems suitable.  It is half again as far from the Sun as the Earth, and so subjected to much less lethal radiation.  It also had an early small ocean and an environment that was possibly more suited to the development of complex chemicals.  Moreover, those who designed and operated NASA’s Curiosity rover, which landed on the red planet in 2012, have concluded that early Mars was a possible “well-spring of life” where “most or all of the major ingredients required to support life” probably existed.


But how would life have traveled from Mars to Earth?  On meteorites.  Large impacts send up a dense cloud of debris and toss some rocks high enough and with enough energy to fly off into interplanetary space.  From there, they orbit the Sun.  A few collide with other planets.  Thus early life might have flows to Earth from Mars.  If so, then, if we trace our origins to the very beginning, we are all Martians.