There are two basic elements that every ecosystem needs (sort of): water and light. Water is the obvious one because, as my high school biology teacher put it, "Life is juicy." Light is the other one, and it's the foundation of the food chain. Plants use light to sustain themselves, herbivores eat plants, carnivores eat herbivores, and humanity makes everything its bitch.
|Om nom nom|
But like I said: sort of.
Let's talk about the ocean floor for a second. For almost all of human history, we've had no idea whatsoever what the hell was down there (other than water). It was, we assumed, dark, flat, and utterly devoid of life. After all, light only penetrates about 3,500 feet down, and the ocean floor is around ten times deeper than that at best.
|Light reaches the second line, or "almost nothing."|
Then in 1977, scientists sent DSV Alvin, a deep sea diving vessel, to the bottom of the Marianas Trench to see what was up down there. Instead of finding an area devoid of life, they found a flourishing ecosystem, filled to the brim with never-before-seen creatures.
|Oh hi! Make yourself at home.|
To be fair, researches probably wouldn't have gotten the grant money to explore the ocean floor if they hadn't already predicted that deep sea life was possible. At that point, plate tectonics was finally thoroughly accepted by the scientific community. That means scientists were aware that the ocean floor actually had some pretty bitching terrain. Of particular interest: deep sea hydrothermal vents.
|It's like the Earth let one rip and it never stopped.|
Vents on the ocean floor that leak extreme heat from underneath the Earth's crust. The theory was that light is only one form of energy, so who's to say heat can't also sustain life? In its trip to the ocean floor, Alvin proved this theory of chemosynthesis (as opposed to photosynthesis) to be right on the money. Instead of plants, there were bacteria and terrifying animals that used heat to sustain themselves.
But wait, there's more! I didn't just choose this topic arbitrarily. Chemosynthesis is considered one of the most important scientific discoveries of all time. Life on Earth began in the oceans. Chemosynthesis may have actually been the original pillar of the worldwide ecosystem.
If you find the origin of life dull, then first of all, shame on you. What the hell impresses you if not the origin of life as we know it? That's some fascinating shit. But second, how about this: If life as we know it can exist without light, then it can exist anywhere with liquid water and heat. Like, say, another planet.
Liquid water, as it turns out, is not super rare. In fact, ever since chemosynthesis was discovered, potential xenobiologists have been giving Europa, one of Jupiter's moons, the "come hither" look. It is downright reasonable to assume that under the thick layers of ice on Europa, there are thermal vents creating a gourmet primordial bisque. If that's the case, it's downright reasonable to assume there may be extraterrestrial life in our solar system.