Are we alone in the universe? Does life exist elsewhere? Is life rare or is it teeming with civilizations or even primitive life forms? It's a mystery that mankind has been wondering about for many years and scientists hope to find an answer to this mystery in the future. So far it is only a fiction but scientists are looking for facts that alien life exists. The field of astro-biology points the way.
Astro-biology is the field of study that deals with how life got started on Earth. The clue to whether there is life elsewhere in the universe is life on earth. The earth has been the perfect place for life to arise and thrive. But it seems that we are unique. Much of the early history of how life got started here has been erased by a natural cycle called plate tectonics. Earth is 4.6 billion years old but most of its original surface has disappeared through plate tectonics. Geology is important in studying life on earth because life from the past is recorded in the rock. Scientists don't know how life formed during the first 1/2 billion years of earth's history and the geologic record is gone so how life got started remains a mystery to scientists.
Earth's unique when it comes to life but what about elsewhere? Mars might have at one time had the hydrothermal conditioning in the past conducive to supporting life but today Mars is too cold and dry to support life. If it ever had life and it remains it must be beneath the surface. However, this isn't likely because Mars does not have plate tectonics or active volcanoes which are important elements for planetary life so scientists must look to other places.
Can snow packs on Mars melt and create conditions for life in the future? Scientists study snow packs on earth for clues. Hot spots and cold spots and other inhospitable areas where simple life forms thrive is what some scientists study. The problem is that inhospitable conditions on alien planets are vastly different by orders of magnitude from inhospitable conditions on the earth. The only kind of organisms that could live in such extreme conditions are psycrophiles but even so, it would take some exceptionally hardy psycrophiles to survive in hostile alien planetary weather conditions.
Plate tectonics on earth act as a grand recycling system and this system also regulates the temperature on earth and keeps carbon dioxide levels uniform. Scientists are looking for other planets in the outer solar system for these kinds of activities. Planets such as Titan, one of Saturn's moons. Titan is like earth in many respects; it has water ice, a nitrogen rich oxygen atmosphere, complex weather systems and volcanism. Europa has an underground ocean 50 miles deep beneath the surface of its icy exterior. It also has active volcanoes. These might be planets that could host life.
Scientists are looking even further for signs of life outside of earth such as exo-planets. There's a host of criteria that an exo-planet needs to meet to be considered. They need to be in the habitable zone of their star system, they need water in some form and the right atmospheric gases (water vapor, carbon dioxide, ozone, oxygen and methane.) All need to be able to sustain life on a terrestrial planet like earth. In the next 20 years scientists at NASA will launch the TPF (Terrestrial Planet Finder) a collection of telescopes that are highly sensitive and advanced. They hope to gather more information about exo-planets and whether they can support life. On earth all life has DNA but will this be true on an alien planet? Maybe somewhere else life doesn't need DNA or even oxygen. Maybe instead of being carbon based it is ammonia based life. Some scientists look for microbial life and others look for great civilizations or intelligent life. But what if we humans are the oldest forms of life in the universe? Many scientists refuse to consider this idea but so far, since we have no proof that alien life exists, maybe we are it.
Many scientists view human life on earth as young life forms amongst far more advanced civilizations but is this the only way to look at the issue? So far we have no proof that other advanced civilizations exist. Perhaps we are the oldest forms of life in the known universe or maybe we are alone and the only other alien life forms will be us, humans, traveling to and fro among the stars, colonizing and living on other planets.