Saturday, February 26, 2011

We May Be Martians

It's possible that all lifeforms on Earth are descended from very distant ancestors that lived on Mars. If Mars was once a warm and wet place, then it could have provided the conditions for life to arise just as well as Earth did. There could have been an independent origin of life on Mars, several billions of years ago, that led to simple, unicellular organisms inhabiting niches across the Martian surface. These organisms, of course, would need to be transported to Earth intact for this theory to hold.

This is where meteorite impacts come into play. It turns out that numerous meteorites have been found in Antarctica that were originally from Mars. An interplanetary rock swap like this can happen when a huge object—like an asteroid or comet—impacts a planet and blasts pieces of its surface into space. Our own moon was formed this way, according to the prevailing hypothesis. Alas, these surface fragments are sent on all sorts of trajectories around the Sun, some of which may eventually cross paths with Earth. If any Mars rocks are large enough to survive entry into Earth's atmosphere, they hit the surface and are thus known as meteorites.

We can be confident these meteorites are from Mars because scientists have analyzed the composition of air bubbles inside them, bubbles that were formed during the catastrophic impact event on Mars. These bubbles are made of the same gases, in the same proportions, as the Martian atmosphere.

The rest of the story explains itself. It's reasonable to question whether lifeforms could survive a catastrophic blast into space, an interplanetary transit of perhaps millions of years, the descent through Earth's atmosphere, and the impact with Earth's surface. What we do know is that many lifeforms on Earth, known as extremophiles, can evolve and thrive in incredibly hostile environments. So there's a chance, albeit a remote one, that we are all Martians. 

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