The short answer is that if we don’t leave the Earth soon, the human race will perish here. As Dr. Stephen Hawking stated in the Spring of 2008 “If we don’t move off world and create self supporting colonies on the Moon, Mars, Asteroids, the Moons of Jupiter and Saturn and some day other star systems, then sooner or later something is going to get us”. Sounds a bit like fear mongering in order to garner support for a particular point of view or project. This is only true though, if there are no real dangers that could threaten our existence as a species. So, can we think of any past threats or disasters that could have been the death of us or our civilization?
Many of us remember the Cuban missile crisis of the early 1960’s, but since we dodged that bullet, we tend to forget just how close to a civilization if not species destroying event it could have been. If the Soviet leader had been just a tad more stubborn and the bombs had been launched, you probably would not be here today reading this essay. Even in the 1960’s there were enough bombs to destroy all of Mankind plus how many other species we don’t know. Today, this danger still has not gone away, though terrorism appears to be more likely. Bioterrorist could potentially create a pandemic that would reduce our civilization to a mere shadow of today’s level.
These are some examples of man made disasters, but there are many others of naturally occurring origins. For example, by studying Mitochondrial DNA, scientist have determined that our human ancestors experienced a population bottle neck about 70,000 years ago. They estimate that there may have been as few as 1000 breeding pairs at one point. We would have been on the endangered species list of the time. What could have caused such a reduction in our numbers? Our best guess is that the explosion of a super volcano in Indonesia around 70,000 years ago filled the atmosphere with 700 – 1000 cubic miles of dust and ash that exacerbated an ice age that had already been underway, reducing the population of many plants and animals. Shortages of food and very cold temperatures reduced our numbers to dangerously low levels. There are many of these super volcanoes around the Earth; the most famous of which is under Yellowstone National Park. This one last blew about 600,000 years ago, but could explode again at any time, since it is still an active volcanic zone today. A society as large as ours that depends on huge areas of cultivation and dependable transportation to distribute food supplies would be much more seriously impacted by such an event than the hunter/gathers of 70,000 years ago. We could easily loose a major portion of today’s population and civilization.
Another example of a recent natural disaster is the 1908 Tunguska event in Siberia. A small meteor or comet appears to have exploded above the ground leveling over 830 square miles of forest. There is no city on Earth big enough that it would not have been totally destroyed by a similar event. This object was a small one, around 30 meters in diameter, causing a reduction of temperatures of a couple of degrees world wide for several years. What if the object had been ten to a hundred times as large; would we or our civilization have survived? Dr. Hawking speculates that in our solar system and any others formed in the same manner as ours, (which may be all of them) every planet will be struck by an object big enough to cause large extinctions once every million years. The reason we haven’t heard from ET may now be apparent. A million years is not long enough for intelligent life to develop; so no messages for SETI to receive. If Dr. Hawking’s extinction theory holds; how then did we not get wiped out during our evolutionary development? Some believe that we were protected by a large Moon and the super planet Jupiter, whose gravitational pull sucked in many of the large objects that might have hit us. The Moon, Jupiter and a little bit of luck and we survive for now; but this combination makes for a poor insurance policy, because the Earth has still been struck by some fairly large objects; just not large enough to get us, yet.
This is just a cursory examination of some of the dangers that we face and that are most likely to occur. There are many more events that are less likely, but could still destroy the Human Race, such as: a nearby supernova explosion, a gamma ray burst or a flare up of the Sun; just to name a few. One or more of these may have caused mass extinctions in the distant past, but we don’t have a way to judge when such events might have occurred or when they might happen again. The most disturbing and most likely possibility is that we might be the instrument of our own demise. By inhabiting outer space and other worlds, maybe we can save ourselves from ourselves.
One of the greatest dangers we face that is of our own creation is that of pollution. If the buildup of CO2 in the atmosphere can be considered pollution as a by product of the burning of fossil fuels, then Global Warming is a pollution problem. If as many have predicted, Global Warming causes sea levels to rise, we could over time loose one quarter to one third of our present living land area. The very areas where most of Earth’s population lives are the areas that will be lost first. With millions of people driven from their homes, we could easily be fighting wars over food, living space and other basic human needs. When things get this bad we will not have the resources to do what we should be doing now – colonizing space and the system’s planets and moons.
Global Warming is not the only type of pollution, though it may be the most pressing. We have also created vast polluted areas related to the mining, refining and manufacturing of many goods and services. The generation of electrical energy is probably the largest contributor to the increase of CO2 in the atmosphere. Then there are the millions of pounds of nuclear waste that have accumulated because we have no proven safe way to dispose of it. We can save the Earth from all this pollution by moving into space, building habitats in space and colonies on the Moon, planets and asteroids. We begin by mining near earth asteroids and the Moon. Using materials thus obtained to manufacture the equipment to build huge solar power satellites to beam power back to Earth to wherever it is needed. We would be removing the major causes of pollution to land and atmosphere to outer space where it can be more easily managed.
Related to the use of resources from space to solve pollution problems is the question of whether there is a developing crisis of depletion of natural resources on Earth. Some would say that the oil crisis in the Summer of 2008 is a prime example of such a depletion of resources. Many experts believe that we have reached the peak production possible and that we will not be able to find new sources of oil fast enough to keep production from decreasing over time. If we can build solar power satellites in space and beam back to earth clean non polluting energy, we can move away from a fossil fuel economy forever.There are many other natural resources without which it would be difficult if not impossible to maintain our present level of civilization much less advance to a higher level. Several of these are grouped into what are called the rare earth metals. Rare earths are used in many chemical processes as catalysts that would be extremely expensive or impossible without them. Some are also used in electric motors and batteries for hybrid and electric cars( http://www.reuters.com/article/newsOne/idUSTRE57U02B20090831 ). The rare earths are not really rare as a function of their abundance in the Earth’s crust, but are very much so in concentrations that can be mined. Known supplies of some of these resources will last for only another 15 – 20 years. How then can we move to an electric economy powered by solar energy to the degree necessary for our future needs? John S. Lewis gives us the answer in his book Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets. He estimates the economic value of one small M-type asteroid 3554 Amun at $20 trillion dollars, $8 trillion worth of iron and nickel, $6 trillion worth of cobalt, and about $6 trillion in platinum-group metals(rare earth metals). "As we enter the 21st century, humankind must deal with the energy crisis, the depletion of natural resources and the pollution of the earth. The solution to all these problems lies beyond the earth by tapping the vast resources of the solar system, in particular the Moon and asteroids, as a source of materials and the sun as a source of power, which will also remove to outer space some of the major sources of pollution. Uncountable dollars worth of metals, fuels, and life-sustaining substances await in nearby space. Vast amounts of these important substances are locked away--for now--in the asteroids, comets, moons and planets of our own solar system. The abundant resources of the solar system, including effectively limitless solar energy, could support a vast civilization of 1016 people"; that's over a million times our present population. John S. Lewis argues in his book Mining The Sky that the "shortage of resources is an illusion born of ignorance."