Resources on Earth are limited. Our planet was born with a fixed amount of water, hydrocarbons, nitrogen, and industrial and precious metals.

And we're collecting, processing, and eventually throwing out those resources at an alarming rate: A United Nations report on resource depletion says that between 1980 and 2008 natural resources per capita declined by 20 percent in the United States, 33 percent in South Africa, 25 percent in Brazil, and 17 percent in China.

For now, only protection and better resource management can safeguard the planet. As we burn through Earth's resources, a wealth of physical resources like metals, water, and hydrocarbons are floating around in asteroids, moons, and other planets, ready to be harvested. If human civilization is to continue to grow and expand over the centuries and millennia to come, hunger for resources is likely to drive us to explore and mine what's way, way out there.

And as wild as it may sound, asteroids in particular could be highly profitable. In 1997 scientists speculated that a relatively small metallic asteroid with a diameter of 0.99 miles contains more than $20 trillion worth of industrial and precious metals.

Yet, space mining is still in its infancy, and exploring it is costly. A NASA mission to an asteroid to bring back 2 kg (about 4.5 pounds) of material in 2021 is expected to cost the space agency $1 billion. But two companies are exploring asteroid mining, as well: Deep Space Industries, and Planetary Resources, which has the backing of several billionaire investors, including Google's Larry Page and Eric Schmidt, software executive Charles Simonyi, and filmmaker James Cameron.

When Planetary Resources was founded in 2012, its founders boldly claimed the company could "add trillions of dollars to the global GDP" and "create a new industry and a new definition of 'natural resources.'" While neither company has gotten off the ground yet, Planetary Resources successfully raised $1 million in crowdfunding to place a new telescope, ARKYD, in space to hunt for Earthlike planets. Peter Diamandis, Planetary Resources' CEO, estimates that an asteroid 98 feet long could contain as much as $50 billion in platinum, and might also yield water for human consumption, or for producing hydrogen fuel.

The potential benefits to asteroid mining reach far beyond just profit, economic growth, and expanding Earth's resource base. While mining on Earth can be highly destructive to natural habitats — resulting in deforestation, soil erosion, chemical contamination, and the pollution of groundwater — mining in space doesn't damage any natural habitats. Even more significantly, less resource bottlenecks means less potential for future resource wars between competing countries — a frightening scenario which the Pentagon has begun planning to address if need be.

In the long run, being able to mine resources in space will help humans create space-based communities, and explore deeper and deeper into the universe, eventually transitioning us away from an entirely Earth-based civilization.