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The layered structure, core mantle and crust, was formed due to internal
melting in the very early history. A cool rocky planet was heated. Heat was
produced by impact energy, decaying radioactive elements (at least 7 times
more abundant than today) and gravitational energy converted to heat. Melting
caused segregation of material. Dense material (iron) was accreted by gravity
inwards, lighter material was moving outwards and resulted in the formation
of a lithosphere (a rocky shell). This segregation is still going on.!
The atmosphere shown in the picture refers to an oxygen-rich
atmosphere. Already at c. 4.5 billion years (Ga) ago Earth was cool enough to
retain an atmosphere consisting mainly of gases released by volcanic activity. It
consisted of water vapour, carbon dioxide (CO2) and sulphur dioxide (SO2)
along with some nitrogen (N2) and other gases.!
When the Earth was cool enough (c 4,4 billion years ago) moisture condensed
(rain) to form the oceans (hydrosphere). As a result the atmosphere was
left with far less H2O gas (water vapour). Once oceans formed the CO2
dropped as well because this (greenhouse ) gas dissolved in the oceans and
then precipitated to create limestone; significant amounts were also absorbed
by rocks during chemical weathering. The removal of CO2 and H2O from the
atmosphere gradually increased the amount of N2. !
It took the appearance of life to add sizable amounts of oxygen (O2) to the air
as O2 is produced by photosynthesis. The first oxygen producing organisms
(cyanobacteria = blue-green algea) appeared between 3.8 and 3.5 Ga and it
took another 1.5 billion years to reach 10% of the present oxygen level. Not
until 0.4 Ga (400 million years ago) the present level was reached.!
3!
Some important biological and physical trends and events in the history of
Earth´s surface environment prior to the “life explosion” c. 545 million years
ago.!
Compare this picture with the figure caption of picture 2 (“From
stardust…”).!
From MacKenzie 2003: Our Changing Planet.!
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The temperature at the surface of Venus is c. 450°C due to an atmosphere
consisting of 97% CO2. On Earth CO2 (apart from being dissolved in the
oceans) is bound to the mineral CaCO3, calcite, precipitated from the water
in the oceans and and later by organisms producing CaCO3-shells etc that by
sedimentation formed limestone.!
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The biosphere overlaps, interacts with and is mainly a result the other
spheres. The solid Earth is mainly represented by the upper surface of the
Lithosphere (the rocky upper 100 km´s of Earth), but also by volcanic
emissions partly derived from the mantle play an important role.!
This combination of an oxygen-rich atmosphere, a hydrosphere, a solid Earth
with plate tectonics (PLT) interacting with a biosphere makes Earth unique
among the terrestrial planets (= Earth-like planets) in our solar system.!
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LAYERING BY PHYSICAL PROPERTIES!
Lithosphere: The outermost 100 km (50-150) rocky sphere consisting of
the crust and the uppermost mantle.!
The Astenosphere (Asteno means soft) is part of the Mantle. This sphere is
a bit softer and more easily flowing but still SOLID.!
Meso means transition as it represents the transtition to the lower Mantle
(also solid) (transition zone)!
Outer core: liquid iron!
Inner core: solid iron!
Although the mantle consists of high density rock it is capable of flowing at a
pace of centimetres/year.!
LAYERING BY CHEMICAL COMPOSITION!
Crust (7-70 km thick): low density rocks. Large differences between
continental and oceanic (below oceans) crust. !
Mantle: high density rocks!
Core: iron (mainly) + nickel!
7!
Earth quake (seismic) waves refract and reflect similar to light. S-waves cannot
transmit liquids, hence it was understood that the outer core is liquid. The
behaviour of different types of waves also revealed all the other spheres within
Earth (the base of the crust etc)!
Iron and stony meteorites found on Earth are fragments of former planets
that have been destroyed by collisions in space.!
Most mining and drilling reach only one km.!
Today there are also high-pressure and high-temperature experiments (also
here at the department) in which deep Earth material is created and studied.
This research refines the modelling and our understanding of Earth´s interior
considerably. !
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James Usshers estimate was printed in the Bible: Earth was created 23
October 2004 BP. As it was also anticipated in the Bible that Earth would not
last very long - 6000 years - the 4004 + 1600 years therefore represented a
major part of the determined time. In addition, as Earth was created by God
the way he wanted it to be, changes from the original conditions were not
expected but from decided catastrophes. These views had important impacts
on science at this time as well as the “truths” stated by philosophers
sometimes more than 1500 years earlier.!
1744 Buffon (Fr) estimated that a sphere the size of Earth of molten iron
needed 10696 years, and a sphere of rocks 74 047 to cool to the present
surface temperature. Radioactivity was unknown - he did not consider an
internal heat production.!
Lord Kelvin 1862: Earth´s surface solidified 98 million years ago but the
accuracy was 20-400 million years. Original temperature was 4000-5000°C.!
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Uniformitarianism:The same, slow processes have been active through
the history of Earth, which during the time of Hutton was considered to be
much longer than a hundred years earlier.!
Plutonism: Earth formed by a molten mass, !
Geological cycle: Rocks solidify from magmas, cool, erode melt etc.!
A remarkable thing is that the explanation of the geological cycle (rock cycle)
required the understanding of Plate Tectonics which was deciphered 200 years
later (mainly 1965-1970). !
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Previously geological time was considered to be equivalent to historical time.!
It was first understood that layers in sedimentary rocks are younging upwards
and that magmatic rocks (e.g. granite) truncating a sedimentary sequence must
be relatively younger - a method called relative dating. Then fossils where
recognised and used to correlate rocks (and times) in different areas.
Radiometric dating to yield absolute ages was not developed with any
precision until after 1950 and with good precision the last 3-4 decades. !
The time table shows that land plants have existed only for the last 10% of the
age of Earth (c. 400 million years), flowering plants only during the last 3%
(144Ma).!
Dinosaurs ruled the Earth during 180 millions years; their extinction was
probably due to a very large meteorite impact. Humans have existed only a
tiny fraction of time but with a tremendous impact. Will we last as long as the
dinosaurs?!
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Wegener was german. PhD in Astronomy; teacher in astronomy and
meteorology. !
Wegener wrote several editions of his book developing the hypothesis which
was based on direct observations. He thought that the rigid continents moved
in the soft ocean floors; the nature of the latter was unknown. He never
reached a reasonable conclusion about the velocity of the movements of the
continents. Neither of the mechanism behind the drift of the continents. He
died during a scientific expedition on Greenland 1930 at the age of 50. This
resulted in a fading out of the debate.!
If he had survived to the age of 85 years he would have experienced the first
physical results proving parts of his hypothesis.!
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Pangaea means all land. All continents were collected in one huge continent.
Wegeners construction to the lower right, a modern construction to the
upper left!
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The fit had been noted by many scientists before Wegner as soon as
reasonably good maps were produced.!
The evidence was rejected because he compared the shorelines which
obviously are very quickly changed by a storm. It was found later in the early
1960`s that the boundary between continental crust and the oceanic crust is
located below the the coastlines (below the soft sediments in the shelves) at a
dept of c. 900m. This was not possible to even guess before the onset of
geophysical measurements that can “see” rocks through the sediments.!
16!
The spreading of plant- and animal fossils is continuous over large distances if
the continents are puzzled together. This evidence was difficult to reject unless
e.g. there had been no ocean floor (water) in the Atlantic and the Pacific at
the times for these animals.!
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The Caledonian - Appalachian mountains formed c 400 Ma ago to a Himalayan
size mountain chain if put together in Pangaea.!
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Glacial features in hot regions mean either that climate has been very different
(e.g. by polar wandering) or that the continents have moved from polar
regions, which has proved to be correct. This glaciation occurred c. 300 million
years ago.!
19!
The mechanism: drifting to the west in the “soft” ocean floor by the attraction
of the Moon was easily proved to be physically impossible.!
Very little debate after Wegener´s death 1930 although a possible (and later
proved correct) mechanism was a convecting mantle (Arthur Holmes 1937).!
Convection is explained below.!
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During WWII and the cold war US navy mapped seafloor with echo sounding
(sonar) to find and hide submarines. Remarkable features were found:!
Oceanic ridges - submerged mountain ranges up to 3000 m above the very
planar ocean floor (East Pacific Rise; Mid-Atlantic Ridge)!
Fracture zones perpendicular to the ridges!
Very deep trenches (<11km)!
Seamounts - drowned undersea islands!
Abyssal plains - vast, very flat areas between ridges and trenches!
And also that dredged rocks of the seafloor included only basalt, gabbro and
serpentinite, no continental rocks like granite typical on the continents.!
It was also found that these rocks never exceeded 200 million years in age
while continental rocks can be up to 3 200 million years. Hence it appears that
the ocean floor is formed and destroyed contrary to the continent which
consist of all ages - very old to very young.!
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1961 it was found that bands of low and high magnetic rocks parallel the
oceanic ridges. These had or have never been seen on land. !
Interpretation: !
1) They stripes show normal polarity (as today) or reversed (counteract the
present field) which are frozen in the rocks when they cool from magma to
rock.!
2) The symmetric pattern with older rocks with increased distance from the
ridge (the oceanic ridge) show that they form at the ridge and spread with the
plates. !
By combining the distance of spreading and the the age it was possible to
calculate the rates of spreading by km/years ending up centimetres/year. (1 12 cm/years known today).!
The record of paleomagnetism (magnetism frozen in magnetic minerals in the
rocks) could also be used to show how continents have moved in the past.
This is not further explained here but it is called polar wandering.!
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Magma building up the oceanic ridge from below freezes the prevailing polarity
of Earths magnetic field at that time, and are moved aside symmetrically when
the ridge is spreading and new magma is crystallising along the ridge.!
Island is located on an oceanic ridge. Half of Island is going to the west and
half to the east. What is unusual is that the ridge is exposed above sea level.!
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The data outlined bands of seismicity (earth quake activity) bounding plates
and coinciding with trenches and oceanic ridges.Volcanism is also following
these bands. I addition it was recorded that the depths of the focus of the
earth quakes varied systematically from shallow to deep across the seismic
bands (across the trenches), while there are only shallow earth quakes along
the oceanic ridges. This lead to the conclusion shown in the following picture.!
26!
Across the trenches (but not the ridges!) the EQ focus (the dots) define
down-going slabs where the lithosphere is sinking into the mantle. Also called
Wadati - Benioff zones.!
Matched with the spreading recorded by the magnetic stripes/ages along the
oceanic ridges it was understood that the ocean floor is constantly formed at
ridges and consumed by subduction along the trenches - hence the ocean
floor never gets older than c. 200 million years.!
Epicenter is the point at the surface vertically above the earthquake focus (=
where the earthquake waves are generated)!
27!
In Subduction zones material from the surface (sediments and water) is
brought down into Earth where it is heated, melted and brought back in melts
that crystallise to rocks at depth and partly is brought back to the surface by
volcanic eruptions (Rock cycle)!
At the surface the hydrological cycle and the rock cycle meet in the process
of erosion resulting in new sedimentation in the sea. !
The rock cycle describes the “recycling” of rock materials:
sediment deposition heating and hardening to
rocks - !
to rock metamorphism
(alteration = new minerals
form due to increase in
temperature and pressure) -
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Approximately 20: 12 small and 7-8 big. All boundaries are not defined yet hence the inexact number.!
Most consist of both ocean floor and continents. The Pacific (and Nasca) plate
consist almost !
entirely of oceanic lithosphere.!
Some differences compared to the continental drift hypothesis:!
• The plates are made up by the lithosphere i.e. the uppermost rigid 100 km
of Earth including the crust and the uppermost mantle - it is not only the
continents that are moving!
• The plates are rigid with no gaps in between - no soft ocean floors!
• The rates are in centimetres/year not metres.!
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Convergent: the cold plate is diving into Earth (subduction) to be
consumed and ultimately melted.!
Divergent: two plates are moving apart - new oceanic crust is formed at
oceanic ridges.!
Transform: two plates are moving aside. This is most typical in the ocean
floor and represented by the fractures across the oceanic ridges. However, the
picture show a transform boundary crossing a continent. This is the case in
California where the transform boundary is the San Andreas Fault. Hence the
many EQ´s in that area.!
These three types of boundaries/movements are required to maintain the
plates movements without gaps being created or the Earth expanding or
shrinking.!
The little picture in the middle shows a close up of the divergent boundary
(oceanic ridge). Melt is formed below the ridge because hot rocks (flowing
solid material) is brought up closer to the surface. Higher up = lower
pressure which results in melting (melting point is lower at lower pressure).!
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The PLT evolution is often described as a cycle starting with rifting (splitting)
of a continental lithosphere to create an ocean (shown above) and ending up
with a closure of that ocean to form a mountain chain.!
The magma below the oceanic ridge is formed due to pressure decrease
(lowering in melt temperature) when the hot rocks of the mantle are moving
upwards by convection. These magmas crystallise to form the new oceanic
crust.!
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Pangaea first rifted into several parts that were drifted away to form the
present distribution of continents.!
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When the plate has been subducted to c 100 km it gets hot enough to
partially melt. As melt and released fluids have lower density (lighter) and!
lower viscosity (more easily flowing) than the mantle they move upwards and
promotes melting of the continental crust resulting in magma formation and
volcanism. The partial melting extracts material with the lowest melting
temperatures. This material also has the lowest density. Material (rocks) with
high melting temperatures and high density will go down into the mantle. !
The partial melting process is thus separating crust-building material from
mantle forming material resulting in a more pronounced layered structure of
internal Earth with time.!
The first step of that evolution (partial melting) takes place at spreading ridges
where basalts are released from mantle rocks. The second step is shown
above.!
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Subduction starts in the ocean floor because the plate is remote (= cold and
dense) from the spreading centre where it formed!
The plate sinks, melts ascends and triggers volcanism that create islands lined
up in an arcuate shape (island arc). The volcanoes are different from those
forming on continental crust or along oceanic ridges.!
39!
There are very large differences between continental and oceanic crust: the
oceanic crust is thinner, have a restricted, “constant” composition (basaltic)
and is much younger because it is formed at oceanic ridges and consumed at
subduction zones. !
The continental crust is much more varied in age and composition. It
represents the low-density material that cannot be subducted into the mantle.
Instead it is floating on the mantle.!
40!
The “final” stage (although there is no end) is when subduction has consumed
all the the oceanic lithospere - the ocean has been closed - and the
continental crust on each sides collide. !
The continental crust has too low density to be subducted into the mantle,
hence the process stops, or rather, continues elsewhere.!
41!
This continent collision is still going on. Apart from (due to) the formation of
the Himalayas it resulted in a very dramatic climate difference in climate on
either side.Very hot on the Indian side and very cold in the Tibetan Plateau.!
The inset picture to the lower left shows how the Indian plate moved from its
location in the Antarctic region (the splitting of Pangaea) to finally hit the
Eurasian plate which resulted in the formation of the Himalayas. !
42!
The old volcano Olympus Mons on Mars shows that it does (did) not. This
huge volcano (much bigger than any on Earth) without small volcanoes in any
direction around shows that there has been many eruptions at one site for a
very long time. If PLT was active, volcanoes should have been spread in trails
(like around Hawaii on Earth) as the volcanic source is stationary for a period
of time while the plates move above. !
So Earth is unique in our solar system. It is the most dynamic planet and also
the most evolved geologically. By studying the other planets we can get
information about earlier stages in Earth history. !
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Complex convection seems the most reasonable based on new geophysical
data.!
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After the very early segregation into crust, mantle and core, the earth interior
has maintained to be very hot as a lot of radioactive material is still left
although it was 7 times higher in the early Earth. The decay of these unstable
isotopes into stable isotopes results in heat production and is the reason why
Earth is still hot inside after 4.6 billion years.!
However, the difference of 7000°C between core and surface means that heat
will be transferred outwards. The core (iron) is a good conductor but the
surrounding rocks in the mantle and crust are not. The heating of the rocks in
the lower mantle will result in a lower density and they start to flow slowly
upwards. They will spread laterally below the rigid and low density lithospere,
help breaking the lithosphere into plates and moving them. The mantle rocks
will also cool when they spread laterally close to the surface of Earth. By that
their density increase and they start to sink again. This way of transporting
heat by movement of material is called convection.!
46!
Or PLT is an effect of the cooling process.You can study convection if you
heat a can of water. When it starts to get hot it is flowing upwards in the
central parts and downwards when it is cooled a bit in the periphery.!
The Earth is actually a cooling body irrespective of climate changes at the
surface. In a very long perspective Earth will change to a solid rocky planet
without plate tectonics like the Moon, Mars and Mercury. The erosion at the
surface (if atmospheric conditions are similar to now) will no longer be
balanced by the formation of mountain building. !
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If PLT was not active on Earth the continents would have been much smaller
or maybe not have existed at all apart from Hawaiian type land.!
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Large earth quakes are real disasters in particular when buildings etc are
located on unsuitable ground. In the past, before PLT was understood, it was
not possible to avoid the most dangerous locations of cities etc. !
Today it is possible to do that but the growth of world population and poverty
means that tremendous amounts of people live on “dangerous” ground. Often
because low altitude land close to the sea level offers fertile soil. Knowledge
and planning is the solution; poverty is the main obstacle but bad planning in
“rich” countries results in loss of life and property.!
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Negative effects because of environmental impacts of SO2, cadmium, arsenic
and mercury.!
Positive effects because so much metal is produced. However these quantities
are not accessible directly after an eruption.!
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These heavy ore concentrates are not possible to mine when volcanism is
going on as shown above. It is impossible to even try to get the ore out also a
considerable time after volcanism has ceased. It is for a very long time too hot
and too dangerous and generally too deep down below the surface.!
The resources mined of these kind today in e.g. Sweden, Canada and Australia
often formed 2 billion years ago and even before that. As they generally form
several kilometres below the surface they must be brought up closer to the
surface by erosion which is a very slow process. In Japan, however,
considerably younger ores are mined in that island arc.!
Ore formation along the oceanic ridges, do not need to be eroded to the
surface and the system are cooling much faster but they exist at a mean water
depth of 3.8 km, and often below the ocean floor. Hence these are generally
not accessible until they are eventually incorporated in a mountain chain when
the ocean closes by plate tectonics. That is, we have to wait several hundred
million years, but today methods are being investigated to mine the ocean
floor. A political problem is who “owns” the ocean floor and its resources.!
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The need for “geo-resources” (non-metallic stone and minerals, metals,
energy) increases faster than world population. These resources are essential
for the development of the society and fundamental for the world economy. !
It is generally well known that metals, oil, gas and coal are “mined” from Earth
but much less known that we are consuming as much of other (non-metallic)
resources from for building purposes, chemical industry, fertilizers, electronic
equipment etc.!
Extracting all these non-renewable resources resources is an example of
Natural capital degradation.!
How would your daily life be affected if the availability of these resources
suffered from a quick decline?!
58!
All metals must be enriched by natural processes to become an ore. In spite
of its frequency in most rock forming minerals, aluminium can only be
extracted from ores by process that are very energy consuming. This is the
major reason for recycling which is also very positive for the environment.!
59!
In US 22 tons a person per year areconsumed. With a population of c. 300
millions the total consumption a year is !
3.3 billion tons/year of non-metallic resources!
96 million tons of metals!
3.3 billion tons of energy resources!
In total a bit more than 7.6 billion tons (7.6 thousand million tons).!
As these 6% of the world population consumes approximately 30% of world
consumption a year the annual world consumption is!
11 billion tons of non-metallic and energy resources and 320
million tons of metals. !
If we calculate the mean annual consumption/capita for the whole world the
figures are!
1.7 tons of non-metallic and energy resources and 48 kg of
metals. In addition to US, the European Union, Japan, China
and India consumes a lot.!
If you now consider that e.g. 0.37% of copper in an ore can be well worth
mining (if there is some additional gold) it is obvious that there will be a large
proportion of waste.Very often this waste is used for other purposes (building
roads etc) but much will be there as just waste.!
Experience shows that approximately the double amount of the extracted
volumes (11.320 tons) of non-metallic and metallic resources will be affected
by mining/quarrying. Thus we can conclude that the volumes of Earth affected
by humans to get these natural resources is in the same order of magnitude as
the plate tectonic processes at oceanic ridges and subduction zones.!
60!
Btu = British thermal unit. 1 Btu = the energy required to raise the
temperature of 1 pound (0,453 kg) of water 1 F = 1055,1 Joule.!
1 Btu/hour = 0,293 watt!
World consumption is thus a bit more than three times the US figures.!
6% of world population consumes 30% of the resources!
61!
Prospect for metals are better than for oil and gas. Today, when demand is
high, prices as well as efforts to find new resources are high. But there is
“peak metal” too with time and it is very important to remember that the
consumption/capita increases and has done so for a long time. So, the
consumption of “geo-resources” increases faster then world population.!
It is easy to realise that it is not sustainable to increase the use of resources
that are being produced on Earth at an incredibly slow pace compared to our
consumption. However, when demand gets too high, prices of metal (and oil)
will be too high and demand will therefore decrease; new materials are
invented. Possibly prospecting will increase resulting in an increase in known
reserves. With decreasing prices the efforts (prospecting) to find new
resources will decrease as well as the known reserves. Sometimes media talk
about known resources when they mean potential resources.!
What will certainly happen (and has already started) in the future is that
prospecting at depth will increase. This is more difficult and costly but apart
from larger problems to keep a mine safe at depth there are also some
possible benefits with respects to environmental issues - the deeper the
mining the less effects on the surface.!
62!
Three major threats in the very long (million years) perspective:!
1.  Sun radiation (solar luminosity) is increasing (more deserts - less water)!
2.  The Earth is a cooling body. !
3.  We may be hit by a meteorite the size of more than a couple of
kilometres.!
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