Cosmic & Natural Events (a bedtime story)
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 cosmic event happens.
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 & 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, USA and Canada.
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 and the USA . 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 would survive for a while, but all signs of civilization would
soon break down.
If the space menace is worrying we
still have to contend with natural disasters on the 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 centres. 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.
And,
so to bed; sleep well!
1,170 words.