The Tidal Irrigation and Electrical System

Many great science-fiction stories have had the premise of hungry, rapacious aliens coming to earth to strip us of everything from our water to our women. However, there are three reasons not to fear this.

• We won’t be edible: LUCA is the most recent ancestor common to all life. Living approximately 3.3 billion years ago, this small single-celled organism is a creature that is the ancestor of every living thing on the earth. Differentiating into plants, animals, bacteria and fungus it retains many features, including cells, RNA, and critically, ATP. This could be considered a common currency in biology. It is the molecular energy that allows cells to work. It is the end product of fermentation, photosynthesis and chemosynthesis so it is the basis of an ecosystem; the way life on earth translates energy in the environment into food. It also allows one creature to eat another. It is highly unlikely that a creature that evolved on another star would share this basic common currency inherited from its version of LUCA. It would need something like ATP but ours would probably be a powerful poison to them or at the very least, be incredibly difficult to digest.
• There is nothing on earth that isn’t freely available in space: In our solar system there are millions of asteroids. Most of those in the asteroid belt are rocky but a few contain large amounts of ice. There are tens of millions of asteroids in the outer solar system that are mountains of dirty ice. Gold, the “rare earths” and every other mineral is plentiful and easily obtained by a species even 50 years ahead of our civilization. What would be the point of aliens coming to earth and upsetting the natives when they could make everything they need in space from freely available materials?
• Earth isn’t that great unless you come from Earth: There are two possibilities about space flight: either there are achievable shortcuts to relativistic effects or there aren’t. If there are, then warp drive or wormhole travel is possible. This is the most dangerous situation for a fledgling species like ours. Warp drive would mean that aliens might not invest in building long-term habitability structures and technology for space. They would look for planets or moons to “terraform” to their civilization’s needs. They would want to wipe all pre-existing life from the habitable body. But, this is very difficult. Life on earth has been found growing in rock at the bottoms of the deepest mines and in the most extreme places. Nuclear reactors, springs more alkaline than a battery, and the mud at the bottom of the deepest part of the oceans are all thriving with earth life. To sterilize the earth you might need to make the entire crust molten, down to the mantle. That wouldn’t make earth a nice place to be. On the other hand, if space doesn’t have any short cuts then spacefaring species would need to learn to make their own habitats. They would need to use the raw materials in space to make cities and societies that could be stable and comfortable enough so that several generations could pass between embarkation and destination. After such institutional living why would a race go through the hassle of colonizing an inhabited world? Why not just find a nice star with no one living there and build your race’s vision of the good life to specification?