By Dr Valerie Jeffries FLS.
Are we alone ?
We no longer believe that Planet Earth holds the only possibility of life, just as we know that our whole Solar System is extremely small in the vastness of space. We already recognise Mars, possibly Venus, and at least three moons of the giant planets Jupiter and Saturn, as possible cradles for life alongside Earth. Appearance of life twice in one Solar System would suggest that life has probably emerged many times among the billions of habitable planets far away, with the possibility of “complex life” (like jellyfish, worms, and beyond). There may well be other “Goldilocks” planets, not too hot nor cold, stable and habitable, but their distance is further than our current technology can contemplate. “Exobiology” must begin near home, with our neighbouring planets.
The successful landing on Mars of NASA’s Perseverance rover has recently brought the hunt for signs of life beyond Earth into the news. Overcoming all the challenges which have led to frequent failure of earlier Mars missions, Perseverance landed perfectly in Jezero crater, near to landscape features suggesting ancient river flow, a delta, and lake formation. Dried lakebeds on Earth would be a promising site for remnants of living organisms, hence Perseverance’s elaborate digging device which will scoop out samples on Mars, that a future mission will retrieve and return to Earth for analysis.
What a prize it would be if indications of life were found! Biochemical markers in the dusty soil perhaps, suggestive of ancient cells, possibly even minute fossil microbes, like Earth’s earliest fossils in rocks 3.5billion years old. Mars is a now a bitterly cold dusty desert, almost all its remaining water being sub-polar or underground, and with just a sliver of carbon dioxide for atmosphere. So nothing currently alive is expected. But just supposing . . . . well – a biologist can dream. Here on Earth we find “Extremophile” bacteria that can survive deadly radiation mimicking the unprotected surface of Mars, and others alive in dry rocks in the deepest mines, or in extreme acid or alkali. All ‘rules’ about conditions for life have been disproved by Earth’s microbes in recent investigations, so besides our optimism about past life on Mars, we may just hope it struggles on, possibly in patches of water under the ice caps.
Curiously, small bits of Martian rock have been knocked off by meteorites, and eventually fallen away from Mars into Earth orbit, eventually crashing down to the ground. Over 200 have been found. We also know Earth has received much larger meteor strikes, like the one that devastated the dinosaurs, so perhaps pieces of Earth rock blasted into space could have ended up on Mars. Certain bacteria can survive in crevices of rock experimentally exposed to space, so rock blasted from a young Earth could carry hardy bacteria that survived a journey to Marsand maybe became established there. Thus microbes on Mars could just conceivably have evolved from Earthlife. Conversely, if young Earth received a chunk of Mars we could all be Martians!
Part 2 and Part 3 to follow.
By Dr Valerie Jeffries FLS.