Long long ago, earth, the moon, the planets and even the sun were all just dust, clumping together from a huge cloud of primeval gas and dust called a molecular cloud. This cloud contained all the materials needed to produce the sun and planets, but a little bit was left over: primeval fragments of the new solar system. Some of these fragments became asteroids, and dwarf planets.Others became comets: wandering pieces of ancient rock and ice, moving through the solar system. A well known example of a comet is 67p, visited recently and studied up close by the Rosetta Mission and Philae Lander.
Now, comets are special. 67p was found to harbour some very special compounds; molecules called precursor compounds. In this case the molecules were organic -or carbon containing- some were precursors to important organic molecules such as amino acids and DNA.
In earth’s earliest days the planet was thought to be something like Hell. It was no place for life, and yet here we are. All of us! Somehow, life on earth took off. Some researchers believe raw materials for life may have been delivered to earth by comets; sprinkled far and wide like a chef going nuts with the salt and pepper.
Now, as far as we know, earth is the only planet in the entire universe known to definitely harbour life. I’ve spoken briefly about some of the conditions for life in other episodes. Check out these links.
But there are a lot of other worlds out there, both in our solar system and beyond, and there’s a lot of stuff floating around in space. We owe our existence to such a collection of stuff, coagulating and sticking together to form the Sun and planets.
Europa is the fourth largest moon of Jupiter. It’s a little smaller than earth’s moon, and the fifteenth largest object in the solar system:
Why am I suddenly talking about Europa? Because astrobiologists (people who examine the possibility of life on other planets) believe that Europa may harbour it. It’s believed to possess an ocean 100 kilometres deep, beneath an icy shell several km thick. This ocean is believed to be salty- like our own. This is important, because the minerals and chemicals dissolved in seawater form an important backbone of deep sea ecosystems concentrated around hydrothermal vents. On earth these vents are practically bursting with life. These vents on earth are geothermally heated, relying on heat from deep within the earth. Ecosystems in this Europan ocean may be heated by Jupiter. This is because the gas giant’s gravity tidally massages the moon, creating heat from frictional forces within the moon.
Just imagine what probes to Europa will find when they eventually take a peek beneath that ice! What I wouldn’t give to see it…
It’s at least possible that around 3.8 billion years ago earth was seasoned with some of the ingredients for life by cosmic passersby. But could it have happened in reverse?
Could this have happened elsewhere in the solar system?.
Life on earth, by and large, is simplistic in structure and function. It has spread to almost literally every corner of our blue-green marble, and it continues to pop up in strange places. Some of them are far too hostile for humans or more complex life forms to survive in. One of the main mechanisms this simple life has used to conquer the globe is simple dispersal. This could be a sneeze distributing countless thousands (millions?) of freshly minted cold viruses far and wide. It could be a gentle breeze, scattering thousands of fungal spores across a forest floor. Many simple organisms spread themselves far and wide by hitching a ride on other organisms. Countless examples exist in nature of organisms that use others to do the work for them. Plants create seeds that are ingested by animals and spread in droppings. Bees not only distribute pollen, they also often carry other organisms: fungi etc, to new locations. Cats and corn are examples of organisms which have conquered the planet alongside humanity, by making themselves favourable.
Most of these mechanisms have developed over time, becoming “the done thing”. But other times throughout the history of life, species have been flung far and wide by accident.
Could Earth seed other planets with life? Imagine if places like Europa have already been seeded with life; not by comets or rogue asteroids, but by Earth. I would like to devote a series of posts to this topic, on mechanisms whereby by organisms from earth could reach other worlds without human intervention.