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Is the world going to end with a bang - or with a whimper? What about that bit in Revelations - The last trump?
The one thing we can assume is that the world will one day 'end' - even if that means waiting around for a few billion years until the sun expands to a red giant and swallows up the earth. But what do people mean when they speak of 'the end of the world'? Let's take a look at some doomsday scenarios.
The impact of a big enough asteroid or comet could create giant tsunamis, global fires, and cause a global winter from the dust it puts in the atmosphere. There is strong evidence that such an impact has occurred several times in the history of the Earth. It is highly probable that such an event was the cause of the extinction of the dinosaurs. The chances are that we would receive little or no warning of such an event. (Sorry Armageddon fans - it just wouldn't be noticed in time for Bruce Willis to go and blow it up). Astronomers have calculated, based on craters on the Moon, that during the last 600 million years the Earth has probably been struck by about 60 objects, 5 kilometers or more across. The smallest of these would release the equivalent of 10 million megatons of TNT, leaving a crater 95 kilometers across. Thats 200,000 times as powerful as the largest atom bomb ever detonated. it's also possible - but incredibly unlikely - that a major collision somewhere in our solar system could fill our system with enough debris to make life difficult on any body in the solar system. Definitely a 'Bang' scenario.
By comparison, the biggest volcanic explosions recorded by history, are tiny. The dust and gases would poison the atmosphere and oceans and bring on a global winter in a way that may cause extinctions. This cause has been proposed for the End Cretaceous, End Permian, End Triassic, and End Jurassic extinctions. There are super-volcanoes at Yellowstone in the USA, Indonesia and New Zealand. Such an explosion may wipe out much of life on Earth but would not affect the Moon or other planets greatly. Definitely a 'Bang' scenario.
from the destruction and radiation, a global nuclear war could throw sufficient dust into the atmosphere to cause a nuclear winter which would prevent crops growing for up to two years and bring about mass starvation. Definitely a 'Bang' scenario.
to have had little effect on bio-diversity. Extinctions suggested to have this cause include: End Ordovician, End Permian, Late Devonian, and others. This one would be a shivering whimper.
living there and destroy the ozone layer in the process. Insects would probably survive. Astronomers tell us approximately 1 gamma ray burst can be expected every 540 million years. This has been suggested as an explanation for the End Ordovician extinction event. A whimper scenario with a spectacular display in the sky.
In this 'global warming' scenario, the level of greenhouse gases in the atmosphere reaches a point where more heat is trapped in the atmosphere than can be radiated back out into space. The result is an unstoppable temperature rise over a period of years or tens of years, which would be sufficient to wipe out most forms of life very quickly. Venus, where temperatures at the surface are high enough to melt lead, is affected by this phenomenon. It's possible that the release of carbon dioxide and methane into the Earth's atmosphere could trigger the release of trapped methane stored on the oceans floors and in permafrost causing this effect. The amount of greenhouse gases in the atmosphere has been much higher in the past however so this is very uncertain. Water vapour is a greenhouse gas - it has four times the effect of carbon dioxide and is far more plentiful in the atmosphere (1-4 % water vapour; 0.04% carbon dioxide). It may be that the Earth's oceans will absorb whatever we release. Again a 'whimper' event.
Solar old age. As the Sun uses up all its hydrogen fuel, helium at it's core will start nuclear fusion causing an increase in solar temperature. The result is a gradual increase in size. This process will continue until, around 5 billion years from now, the Sun will be 100 million miles across - encompassing the entire orbit of the Earth. Life will have been extinguished on our planet long before that. The seas will boil off and all gas will be blown away from the Earth by solar storms. It is estimated that 1 billion years from now, the temperature of the Earth will be similar to present-day Venus making life untenable. Given a billion years this will be a long drawn out 'whimper' where our descendants (if we have any by then) will probably bear little resemblance to us today.
Alien invasion. Could it be the might be an alien invasion on the lines of 'Independence Day', 'Battlefield Earth' or 'War of the Worlds'. If we were to face a hostile advanced intelligence would we really have any chance against them? Probably a 'Bang' event. Personally it is my belief that any civilization advanced enough to cross interstellar space would also have advanced socially and be less warlike than humans.
So lets see - that's 4 'bangs', ten 'whimpers', a 'last trump' and an 'off'. It seems the whimpers have it.
Further reading :
Doomsday Movies to Watch
Armageddon
Volcano
The day after tomorrow
2012
Independence Day
Waterworld