Meteorite impact
In the history of the Earth, it is widely accepted that several large meteorites have hit Earth. The Cretaceous-Tertiary asteroid, for example, is theorized to have caused the extinction of the dinosaurs. If such an object struck Earth it could have a serious impact on civilization. It's even possible that humanity would be completely destroyed: for this, the asteroid would need to be at least 1 km (0.6 miles) in diameter, but probably between 3–10 km (2–6 miles). Asteroids with a 1 km diameter impact the Earth every 0.5 million years[4] on average. Larger asteroids are less common. The last large (>10 km) impact happened 65 million years ago. So-called Near-Earth asteroids are regularly being observed.
Some scientists believe there are patterns in the number of meteorites hitting Earth. An interesting explanation of such a pattern is given by the hypothetical star Nemesis. This hypothesis states that a star named Nemesis regularly passes through a denser part of the Oort cloud, causing meteorite rains to collide onto Earth. However, the very existence of this pattern is not widely accepted, and the existence of the Nemesis star is highly contested.
A star passage that will cause an increase of meteorites is the arrival of a star called Gliese 710. This star is probably moving on a collision course with the Solar System and will likely be at a distance 1.1 light years from the Sun in 1.4 million years. |
Less Likely Threats from Space
A number of other scenarios have been suggested. Massive objects, e.g., a star, large planet or black hole, could be catastrophic if a close encounter occurred in the solar system. Another threat might come from gamma ray bursts; some scientists believe this may have caused mass extinction 450 million years ago.
Still others see extraterrestrial life as a possible threat to mankind; although alien life has never been found, scientists such as Carl Sagan have postulated that the existence of extraterrestrial life is very likely. In 1969, the "Extra-Terrestrial Exposure Law" was added to the Code of Federal Regulations (Title 14, Section 1211) in response to the possibility of biological contamination resulting from the US Apollo Space Program. It was removed in 1991 because scientists consider such a scenario technically possible, but unlikely.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Risks to civilization, humans and planet Earth". |
Other Threats to the Earth from Outer Space
There are many scenarios that have been suggested that could happen in the future. Some are certain to happen and will almost certainly end humanity, but may only happen on a very long timescale, or may happen sooner. Others are likely to happen on a shorter timescale, but will probably not completely destroy civilization. Still others are extremely unlikely, and may even be impossible.
Some foreseen hazards (hence not members of the current category) which have been excluded from the list of bangs on grounds that they seem too unlikely to cause a global terminal disaster are: solar flares, supernovae, black hole explosions or mergers, gamma-ray bursts, galactic center outbursts, supervolcanoes, buildup of air pollution, gradual loss of human fertility, and various religious doomsday scenarios. - Nick Bostrom
Space
It is certain that events in space can cause life on Earth to come to an end. The certain events, however, will happen at an extremely long timescale measured in billions of years. Projections indicate that the Andromeda Galaxy is on a collision course with the Milky Way. Impact is predicted in about 3 billion years, and so Andromeda will approach at an average speed of about 140 kilometres (87 miles) per second; the two galaxies will probably merge to form a giant elliptical. This merging could eject the solar system in a more eccentric orbit and an unwanted position in the merged galaxy causing our planet to become uninhabitable (an actual collision is unnecessary).
In about 5 billion years, stellar evolution predicts our sun will exhaust its core hydrogen and become a red giant. In so doing, it will become thousands of times more luminous. Even in its current phase of stellar evolution, the sun is increasing in luminosity (at a very slow rate). Many scientists predict that in fewer than one billion years, the runaway greenhouse effect will make Earth unsuitable for life.
On an even longer time scale, the universe may come to an end. The current age of the universe is estimated as being 13.7 billion years old. There are several competing theories as to the nature of our universe and how it will end, but in all cases, there will be no life possible. These scenarios take place on a considerably longer timescale than the expansion of the sun.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Risks to civilization, humans and planet Earth". |
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