Transcript ESP_3_Geologic Time_v2x

3. GEOLOGIC
TIME
John Playfair stares
into the abyss of time
at Siccar Point,
Scotland
AGE OF THE EARTH – 4004
BC. OR OLDER ?
James Ussher (1581-1656), Anglican
Archbishop of Armagh in Northern
Ireland, and Primate of All Ireland.
His precise dating of the moment of
the Creation as occurring at nightfall
preceding Sunday, October 23, 4004
BC, is included in the margins of
fundamentalist Bibles. Published
posthumously in 1658, Annals of the
World is an extraordinary work
attempting to give an account of major
events in history from 4004 BC to
1922 BC, and from then an almost year
by year account up until 73 AD..
OTHER ESTIMATES OF THE
AGE OF THE EARTH BASED
ON THE BIBLE
The Venerable Bede (723 )
3952 BC
Johannes Kepler (1596)
April 27, 3977 BC
John Lightfoot (1644)
3929 BC
James Ussher (1658)
October 22, 4004 BC
Isaac Newton (1687)
4000 BC
OTHER ESTIMATES
In 1774 Georges-Louis Leclerc,
Comte de Buffon (1707-1788),
concluded that the Earth was
probably about 75,000 years old.
His estimate was based on
experiments on the cooling rate
of iron. He also proposed that the
planets had originated when a
comet had struck the Sun. But
Buffon’s most important work was
in biology, published as the
Histoire naturelle, générale et
particulière in 36 volumes
between 1749 und 1788. His
observations anticipated the idea
of evolution. His age of the Earth
was rejected by the authorities
at the Sorbonne
The importance of time
The idea of a vast expanse of time has been the
major philosophical contribution of geology
Geologic change is not perceptible on human
timescales
Geology began as a science during the
Scottish Enlightenment in 1785 – with the
recognition that Earth had a long history
James Hutton
Geologist
David Hume
Philosopher
Joseph Black
Chemist
Adam Smith
Economist
THE DISCOVERY OF THE
DEPTHS OF TIME - ETERNITY
The recognition of the immensity of geologic time seems
to have occurred one clear day in the summer of 1788,
when three people who considered themselves ‘geologists’
sailed along the Scottish coast east of Edinburgh and
landed at a place called Siccar Point.
James Hutton (1726-1797) is now known as the ‘Father
of Geology’, Sir James Hall of Dunglass (1761-1832),
President of the Royal Society in Edinburgh, and
mathematician John Playfair (1748-1819), Hutton’s close
friend. There they saw steeply inclined beds of slate,
covered by gently sloping red sandstone.
Sir James Hall’s sketch (1788) of the rocks at Siccar Point
SICCAR POINT TODAY
In 1805 John Playfair
described their
experience: “The mind
seemed to grow giddy
by looking so far into
the abyss of time.”
James Hutton stated
"we find no vestige of a
beginning, no prospect
of an end." The Earth
might be eternal.
James Hutton – The Father of Geology
Hutton’s book: Theory of the
Earth with Proofs and
Illustrations, published in
1795, was a bit of a disaster
– poorly written and missing
many of the illustrations
(they were discovered in a
printers shop in Edinburgh a
few years ago).
John Playfair successfully
rewrote it as Illustration of
the Huttonian Theory of the
Earth, published in 1802
1789 - A TIME FOR REVOLUTION
A year after Hutton,
Playfair, and Hall visited
Siccar Point, on July 14,
1789, the great prison in
Paris, the Bastille, was
attacked and torn down.
The French Revolution was
under way.
One of the revolutionaries
was Jean Léopold Nicolas
Frédéric Cuvier. He was 20
years old.
At the age of 30 he was appointed Professor at the Botanical Garden in Paris
(formerly the Royal Gardens), which then came to house the Muséum nationale
d’histoire Naturelle . He was an avid collector of fossils, and an observant
geologist.
CUVIER’S CATASTROPHISM
For the French aristocracy, the 1789
Revolution was a catastrophe, as was
the Reign of Terror of 1793-94.
Cuvier survived all that as an
observer, but the idea of
catastrophic change was in the air.
Cuvier became a close friend of
Napoleon, and convinced him to send
back to Paris the natural history
collections from cities and towns in
the areas he conquered.
These greatly enhanced the
collections already in Paris and made
the Muséum d’Histoire Naturelle one
of the worlds greatest museums.
The word ‘catastrophe’ is derived from the Greek
and means turning things upside down. A
catastrophe is defined as a sudden event with dire
consequences.
Cuvier held to the idea that the Earth was about
6,000 years old, so catastrophes were required to
fit in all that had happened since the planet had
formed. He noted that the fossil faunas of the
strata surrounding Paris, mostly molluscs and
vertebrates in the marine strata, were the same
from top to bottom. The retreat of the sea and
subsequent flooding is often represented by thin
strata or even bedding planes between the strata.
He concluded that the transgressions and
regressions occurred very rapidly in response to
catastrophic geologic movements.
We now know that the fossiliferous rocks in the Paris Basin are a very incomplete
record; most of the geologic time is represented by ‘hiatuses,’ lengthy gaps in the
record represented only by thin sediments or surfaces between the major rock
units. Cuvier had thought these boundaries represented very short periods of
time; today we know they represent much more time than do the deposits. The
misinterpretation of Cuvier’s ideas of two hundred years ago has been recently
resurrected as ‘Intelligent Design.’
CATASTROPHISM REPLACED BY
IMPERCEPTIBLY,SLOW GRADUAL CHANGE
Charles Lyell (1797-1875) was the
first ‘modern’ geologist. He argued
that the geologic process of the
past were the same as those of
today. Geologic change was
imperceptibly slow. This idea
became known by the unwieldly
term
‘Uniformitarianism’
His book Principles of Geology
presnets cogent arguments that
the change of climate implied by
the tropical coal beds of England
to its modern climate were due to
changes in the distribution of land
and sea.
Global climate change was the major topic of
the first general book on geology
The piddling school of geology
Bless the baby what a valley he have a-made !!
Cause and Effect
Not everyone agreed with Lyell’s idea that geologic processes were very slow.
Henry de la Beche’s cartoon (circa 1830) shows a little boy urinating, lampooning
Charles Lyell’s idea that processes that have shaped the Earth throughout its
history are the same as those acting today
1826 – 1840 Discovery of the
Ice Age
Even before publication of Lyell’s
books, disturbing new evidence of
climate change had come to light.
Around the Alps, in northern Europe
and in parts of the British isles there
were strange landforms - U-shaped
valleys, long ridges of sand, gravel
and boulders, and occasional huge
blocks of rock resting on the soil.
These features were attributed to
the Biblical Flood; the deposits were
called “drift” and their age given by
Lyell as “Diluvian,” the time of the
deluge, that is, the Biblical flood.
Some of these things were hard to
explain. The boulders, for example,
were thought to have been
transported by icebergs in the flood
waters - but then came the question:
how did icebergs get into the flood
waters?
Louis Agassiz (187-1873)
Giebichenstein, near Stöckse,
Niedersachsen, Germany
Glenwoodville, Alberta - 1881
The Train of Erratics, Alberta
In Switzerland naturalists were discussing the similarity
between the deposits of the Swiss Midlands and the
materials surrounding the glaciers in the Alps. They were
discovering what the farmers in the alpine valleys already
knew. Glaciers were ‘living things.’ They advanced and
retreated, and their deposits could be found far down the
valleys they occupied.
In 1826 Ignace Vernetz proposed to a meeting of the Swiss
Natural History Society that the glaciers had been much
larger and covered the whole region. Word passed from one
scholar to another until Louis Agassiz heard about it.
Agassiz was Professor at the Lyceum of Neuchatel, and a
paleontologist who specialized in studying fossil fish. He
thought the idea was ludicrous, but after a field trip into the
Alps with Jean de Charpentier, one of the hypothesis’
proponents, he became convinced it might be right and spent
several years gathering further evidence.
Rhone Glacier – 1913 - 2006
A glacial erratic beside a glacier, Alaska
Then, in 1840 Agassiz attended a meeting of
the British Association in Glasgow, Scotland.
After the meeting he traveled through
Scotland with Buckland, and Roderick
Murchison, a Scottish gentleman geologist. With
Agassiz’s interpretation of the Scottish
landscape as having a glacial origin everything
suddenly made sense.
The U-shaped valleys had not been carved out
by the tiny streams in them today but by moving
ice; the strange longitudinal hills of detritus
were glacial moraines; and those odd boulders
scattered about the landscape had been
transported by the glaciers. Buckland became
an enthusiastic supporter of the glaciation
hypothesis, and he eventually converted Lyell.
Agassiz met Professor William Buckland of
Oxford University at a naturalists meeting in
Freiburg-in-Breisgau on the Rhine in Germany
not far from the Swiss border. Buckland,
originally a catastrophist, was gradually
changing his mind about how the Earth had
evolved. He had been Lyell’s teacher (and had
been given Henry de la Beche’s cartoon).
Agassiz invited Buckland to come with him into
the Jura mountains to look at the evidence that
glaciers had been there. Buckland was not
convinced, but displayed an open mind. When
Lyell heard about the idea of widespread
glaciation he felt it was a challenge to his notion
of gradual change, almost a return to
catastrophism. Other British geologists also
rejected the idea.
THE DISCOVERY OF PAST WARM POLAR REGIONS
Just as the idea of large ice sheets
during the Earth’s recent and ancient
past was becoming accepted, evidence
was found that Earth had also been
much warmer in the past. Adolf Erik
Nordenskiöld (1832-1901) was born in
Finland, but later emigrated to
Sweden. He was a geologist and Arctic
explorer. In 1870, in a search for the
Northwest Passage, he landed on
western Greenland’s Nûgssuaq
(Noursoak) Peninsula (70.5° N), north
of Disco Island. In the Cretaceous
strata there he found a fossil flora
rich in tropical plants, including the
remains of breadfruit trees.
Through the 19th century a
sequence of geologic strata
was put in order and a
relative geologic timescale
developed.
Geologists believed it
involved many hundreds of
millions of years.
The physicist Lord kelvin
argued that the Earth was
about 100 million years old.
THROWING A MONKEY WRENCH INTO
EXPLAINING CLIMATE CHANGE
James Dwight Dana (1813-1895) was an American
mineralogist, a Professor at Yale, and, best known
for his book Dana’s System of Mineralogy. He also
published a Manual of Geology (1863) in which he
introduced a concept that was to become both a
tenet of American geology and a monkey wrench in
development of any understanding of climate change
— the permanence of continents and ocean basins. In
contrast to Lyell’s idea that land could become ocean
and vice versa, Dana believed that the continents
and ocean basins had formed when the Earth
solidified. The more dense rock formed the
continents and the less dense rock was to form the
basement of the ocean basins. His idea was that the
more dense rock did not contract as much as the
less dense rock, hence as the Earth cooled, the less
dense rock formed basins which collected water.
These different types of basement rock had
remained fixed in size and position ever since.
‘CRUSTAL MOBILITY’
TO THE RESCUE
In Marburg, Germany, just before
WWI, Alfred Wegener and his father
in law, Validimir Köppen plotted maps
showing the distribution of the thenknown climate sensitive sediments and
fossils. They came to a remarkable
conclusion. The Late Paleozoic glacial
deposits of India, Australia, South
Africa and South America could
better be explained if these
continents were simply fragments of a
much larger southern hemisphere
continent, Gondwana. Furthermore,
the similarity of deposits of North
America and Eurasia could be readily
explained if there had been no
Atlantic Ocean separating them.
THE RETURN OF CATASTROPHISM AND
THE IDEAOF RAPID CHANGE
In 1969. Digby McLaren, a prominent
Canadian geologist and Paleontologist
postulated that an asteroid impact was
responsible for the great extinctions
near the end of the Devonian Period,
about 360 million years ago.
The idea received mixed reviews from the
scientific community.
However, in 1980 Walter Alvarez and his
father, Luis, presented evidence that an
asteroid had struck the Earth at the end
of the Cretaceous period, 65 million years
ago, causing the extinction of dinosaurs
and many other forms of life. Skeptics
that such a thing could happen had second
thoughts when the fragments of the
comet Shoemaker-Levy began crashing
into Jupiter on July 16, 1994.The
disturbances in Jupiter’s atmosphere
were larger in size than planet Earth
itself. It was a sobering experience for
everyone who thought that catastrophes
were fantasy
THE NATURE OF THE GEOLOGIC RECORD
Older sediment is eroded to make young sediment
THE GREAT EXTINCTIONS AND THEIR CAUSES
SUMMARY
Through the 19th century –
A long and complex history without
specific ages