"It is as inescapable as the laws of physics that humanity will one day confront some type of extinction-level event. But will we, like our ancestors, have the drive and determination to survive and even flourish? . . . On a scale of decades, we face threats that are not natural but are largely self-inflicted [including] global warming . . . modern warfare as nuclear weapons proliferate in some of the most unstable regions of the globe, [or] weaponized microbes [that could conceivably] wipe out 98 percent of the human race. . . . On a scale of thousands of years, we face the onset of another ice age [or] the possibility that the supervolcano under Yellowstone National Park may awaken from its long slumber . . . . On a scale of millions of years, we face the threat of another meteor or cometary impact . . . . We now know that there are several thousand NEOs (near-Earth objects) that cross the orbit of the Earth and pose a danger to life on our planet. . . . If there is one lesson we can learn from our history, it is that humanity, when faced with life-threatening crises, has risen to the challenge and reached for even higher goals. In some sense, the spirit of exploration is in our genes and hardwired into our soul. [So] now we face perhaps the greatest challenge of all: to leave the confines of Earth and soar into outer space. . . . Perhaps our fate is to become a multiplanet species that lives among the stars."