Space and survival is the idea that the long-term survival of the human species and technological civilization requires the building of a spacefaring civilization that utilizes the resources of outer space, and that not doing this will lead to human extinction. A related observation is that the window of opportunity for doing this may be limited due to the decreasing amount of surplus resources that will be available over time as a result of an ever-growing population. The earliest appearance of a connection between space exploration and human survival appears in Louis J. Halle, Jr.'s 1980 article in Foreign Affairs, in which he stated colonization of space will keep humanity safe should global nuclear warfare occur. This idea has received more attention in recent years as advancing technology in the form of reusable launch vehicles and combination launch systems make affordable space travel more feasible. Risk to humanity With space and human survival comes risk to the human species. A severe event in the future is one that could cause human extinction which is also known as an existential risk. Humanity's long track record of surviving natural hazards suggests that, measured on a timescale of a few centuries, the existential risk posed by such hazards is rather small. Nevertheless, researchers have experienced an obstacle in studying human extinction as humanity has actually never been diminished during all of recorded history, although this does not mean that it will not be in the future with natural existential scenarios such as meteor impacts and large-scale volcanism, anthropogenic events like global warming and catastrophic climate change, or even global nuclear warfare. Many of the same existential risks to humanity would destroy parts or all of Earth's biosphere as well. Although many have speculated about life and intelligence existing in other parts of space, Earth is the only place in the universe known to harbor life. Eventually the Earth will become uninhabitable, at the latest when the Sun becomes a red giant in about 5 billion years. Mankind, or its intelligent descendants, if they still exist at that point, must leave the Solar System long before that to ensure survival of the human species. Space settlement Human extinction can be prevented by improving the physical barrier or increasing the mean distance between people and the potential extinction event. For example, pandemics are controlled by placing exposed people in quarantine and evacuating healthy people away.