Cosmic & Natural Events

 

Cosmic & Natural Events (a bedtime story)

 

By Len Morgan

 

On 16th May 1996 an asteroid the size of the millennium dome was heading for an impact with the Earth.  Not science fiction, we were just 6 hours away from mass extinction.  World governments watched powerless to change what was coming.  The scientific community were impotent; all watching with bated breath.

No warning was given, where could we have gone anyway?  We were lucky; humanity survived that 'chance in a million' close encounter.  Chance in a million?  In fact, close encounters (near earth events) are more common than most people know.

Impacts on a smaller scale are not as rare as you might think, but every 60,000 years or so, a significant extinction takes place.  There have been five major extinctions as a result of these:

 1) The Ordovician extinction of 440 Mya (million years ago) resulted in 80% extinction, that means only 20% of species survived.

 2) The Devonian extinction 365 Mya saw 85% extinction.

 3) The Permian extinction 245 Mya resulted in the death of 95% of species including two-thirds of the insects; the nearest yet to complete obliteration.   This was the big one that heralded the age of the Dinosaurs.

 4) Triassic extinction 210 Mya 70% of life on Earth disappeared.

 5) Cretaceous extinction 65 Mya a 20-kilometre rock hit the Yucatan, resulting in 70-75% extinctions bringing the Cretaceous to an end, and with it the reign of the Dinosaurs.  But, it's not all bad news, it was this event that enabled mammals to inherit the Earth, enabling our ancestors to become the dominant species; without it, dinosaurs would still be ruling the Earth.

In between the big extinction episodes, there have been at least twenty other smaller extinctions episodes that we know of.  For example grazing animals, including horses, were almost wiped out in one that happened about 5 Mya, can you imagine human history without horses, cows and sheep?  Bear in mind these are just geologists estimates, based on the fossil record.  At the end of the Permian for instance, there were reckoned to be between 45,000 and 240,000 species (species not individuals) inhabiting the planet 95% were wiped out.  The survivors from each species may have been just a few scarred and limping individuals teetering on the brink of oblivion.

The tally, for conservationists, is: (as far as educated guesses go) total number of species that have existed since life on earth began between 30 and 4,000 Billion of which 99.99% are no longer with us (according to Bill Bryson’s book ~ A Short History of Nearly Everything [p415-418]).

When a major Cosmic extinction takes place, life is never the same again.  If you're still harbouring a belief that it couldn't happen take note, we are well past time for the next big one.  Maybe the warning provided by the comet (Shoemaker-Levy 9), which had a close encounter with Jupiter in 1992, fragmented and returned like a string of pearls in July 1994. The string crashed into Jupiter leaving a scar the size of Earth, (watch it on YouTube), It’s a wakeup call!

Through history, comets have been viewed as omens of doom.  As recently as 1908 a 50-meter rock landed in the forests of Siberia devastating a vast area and producing shock waves recorded in Paris, Vienna, London, New York and Montreal.

A close encounter inevitably changes the orbit of an asteroid (imperceptibly), modifying its approach vector on its next orbit.  

So, let’s imagine a major impact close to the coast of the UK, and look at a likely time-line and the events as they unfold in the first hour:

8 seconds after the Impact:

Millions of tonnes of debris and superheated steam would be hurled into space.  By its speed alone the ejected material would be heated to 3,000 degrees Fahrenheit.

Impact +43 seconds:

Shock-waves devastate the UK Europe, and Ireland would sink into the sea.   The UK and European Cities would be flattened.

Impact +10 minutes:

The debris hurled into space would re-enter the atmosphere.  Firestorms would ravage Europe, Asia, and the Americas.  All communication with Europe would cease.

Impact +15 minutes:

Earthquakes and tidal waves would engulf Europe and the USA, Africa, Mexico and much of South America

Impact +20 minutes:

Shock-waves kill most of the survivors in the USA, Canada and Greenland.

Impact +60 minutes:

Dust-clouds occlude the sun, the beginning of a long dark winter that would last for decades.  Survivors in the Southern hemisphere might survive for a while, but all semblance of civilization would soon disappear.

If the space menace is worrying we still have to contend with natural disasters on Earth: Tsunamis, tornadoes, and earthquakes.   But, of course, none of those happen here, do they!?

 In the 1960's Bob Christiansen of the US Geological Survey was puzzling about the absence of a volcano in Yellowstone National Park, despite its obvious volcanic nature, curiously nobody had ever asked that question before.  Most of us think of the classic shape of Mt Fuji, there are some ten thousand of these intrusive volcanoes in the world.  But, there are others that don't build mountains.  They burst open in an explosive rupture leaving behind vast subsidence into a pit called a Caldera.  But, Christiansen couldn't find a Caldera anywhere in Yellowstone.  Coincidentally, at the same time, NASA was testing high altitude cameras by taking photo's of the area, a thoughtful official passed on copies to the park authorities, suggesting they might make a nice display at the visitor centre.  At first glance, Christiansen understood why he couldn't locate a caldera.  Virtually the whole park -- 9,000 square kilometres -- was the Caldera.  The explosion had left a crater 65 kilometres across; much too large to be seen at ground level.  At some time in the past Yellowstone must have blown with violence far exceeding anything in recorded history.  

Yellowstone is a Supervolcano sitting atop of a hot spot, a reservoir of molten rock some 200 kilometres below ground, rising to near the surface and forming what is called a superplume.  The heat from this hotspot is what powers all the vents, geysers, popping mud pots and hot springs.  The magma chamber is 72 kilometres across slightly larger than the park.  Imagine a pile of TNT the size of New Jersey 10 Kilometres high, reaching up into the clouds.  This is what visitors to Yellowstone are walking on.  If it blew the cataclysm could not be imagined.  Such plumes are not all that rare; there are about 30 known and active.  They are responsible for many of the worlds best-known island chains -- Iceland, Hawaii, the Azores, the Canaries, and the Galapagos archipelagos.  Apart from Yellowstone, they are all oceanic.  They bubble away benignly whereas Yellowstone explodes.  It doesn't happen often, but stand back when it does.  Its first known eruption was 16.5 Mya, it has blown about a hundred times since each was between 280 and 2,500 times as large as the Mount St Helens eruption, but 8,000 times as devastating.

And, so to bed; sleep well!

 

Copyright Len Morgan