View
218
Download
0
Category
Preview:
Citation preview
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 1/22
This is the hard solidouter part of theEarth. It is made ofrock and supportsthe oceans. It isbetween 5 and 70 kmthick.
This is a thick layer(3000 km) of very hot
rock called magma. Itbehaves like a solidbut can flow in partsvery slowly.
This is very hot, liquid,and is made of iron. It is
about 1,500 km thick.Temperatures in theinner and outer core arebetween 5,000 and7,000 ºC
This is a ball of veryhot iron and nickel. Itis about 2,000 km thick.It is solid because ofthe immense pressure.
The EarthCrust
InnerCore
Mantle
OuterCore
Why are the inner parts of the Earth hot ?
- because it is still cooling down from when it was first formed- because heat is generated by radioactive processes deep within the Earth
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 2/22
The Earth‟s layers were formed early in the history of our
planet. Heavy matter sank to the centre of the Earth while
lighter material floated on top. This is why the mantle andcore are much more dense than the crust.
All of the minerals and ores that we depend on in our
modern world come from the crust of the Earth. Man has not
penetrated even a third of the way through the crust, so other
methods have had to be used to understand the structure
inside the Earth.
Scientists use evidence from earthquakes. The seismic
waves which travel through the Earth are affected by its
structure, allowing scientists to build up a detailed picture of
the inside of the planet (a bit like an ultrasound scan builds up
a picture of an unborn baby).
Scientists have also made detailed measurements of how the
Earth affects the orbits of other bodies in space, and from
this have been able to work out the mass of the Earth and
calculate its average density. This density is much higher than
the density of the rocks in the crust, which means the inner
layers must be much less dense.
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 3/22
It is clear that the surface of theEarth is not flat – mountains andvalleys, shallow seas and deepocean trenches all indicate that the
relatively thin crust of the Earthhas experienced vast forces whichhave shaped it, and continue to doso.
At one time scientists thought thatfeatures like mountain ranges werecaused by the crust wrinkling as itshrunk when it cooled down – much like the skin on cooling
custard.
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 4/22
A number of key pieces of evidence led Alfred Wegener in 1915
to propose an alternative theory:
- The coastlines of some continents fit together remarkably
well (e.g. Africa and South America)
- Fossils of the same plants and creatures were found where
these continents appeared to fit together, with no satisfactory
explanation of how they could have travelled between.
- The same rock structures were also found
Wegener‟s idea that the continents could move and that they previously been part of
larger „supercontinents‟ was called continental drift.
Geologists found it hard to accept Wegener‟s ideas because Wegener could not
explain how the continents had moved. In addition, geology was not the field of science in which Wegener was recognised as a specialist.
It was 1944 before scientists discovered the driving force which could move
continents (natural radioactive processes causing convection currents). Other
scientists found that the sea floor was spreading apart, and molten rock was spewing
out between continents. The theory of plate tectonics was born.
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 5/22
Plate tectonics
The continents moved and split up very slowly – a few centimetres each year. They
moved because the Earth‟s crust and uppermost part of the mantle is cracked into a
number of large pieces called tectonic plates. They continue to move, some apart
from each other, and others in collision with each other.
The plates float on the mantle, which behaves as a very thick liquid. Naturalradioactive processes deep in the Earth produce vast amounts of heat which cause
the molten rock to expand and become less dense. This rises, causing convection
currents. The tectonic plates ride on these convection currents.
convection currents in the mantle
cause the plates to move
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 6/22
Plate tectonics
The continents moved and split up very slowly – a few centimetres each year. They
moved because the Earth‟s crust and uppermost part of the mantle is cracked into a
number of large pieces called tectonic plates. They continue to move, some apart
from each other, and others in collision with each other.
The plates float on the mantle, which behaves as a very thick liquid. Naturalradioactive processes deep in the Earth produce vast amounts of heat which cause
the molten rock to expand and become less dense. This rises, causing convection
currents. The tectonic plates ride on these convection currents.
Location of volcanoes is clearly
linked with tectonic plate boundaries
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 7/22
to erupt (watch the movie “Dante‟s Peak”). It is difficult to predict exactly when avolcano will erupt, however.
Sudden movements of plates past each
other causes earthquakes. If earthquakes
happen under the sea, tsunamis may be
caused. It is difficult for scientists to know
exactly where and when the plates will move
like this, so predicting earthquakes is adifficult job.
Where the plate boundaries meet, huge
forces make the plates buckle and deform.
Mountains may be formed when plates
push each other upwards.
Volcanic eruptions may occur when
magma is able to force its way to the
surface. From a variety of clues scientists
are able to tell when a volcano is threatening
Interested ? www.volcanolive.com
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 8/22
Nitrogen
OxygenNoble Gases
Carbon dioxide
78%
21%
0.9% 0.04% The Atmosphere
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 9/22
H2
He
The very first gases in the Earth‟ atmosphere, left over from the cloud of
gas and stellar dust from which the Earth formed, were hydrogen and
helium.
These very low density gases were light enough to escape from the
Earth‟s atmosphere and were lost into space.
4500 million years ago...
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 10/22
H2O(g)
CO2 trace
NH3 trace
CH4
4000 million years ago...
N2
Intense volcanic activity released hot gases into the atmosphere. Theatmosphere is thought to have contained nitrogen and carbon dioxidemainly, along with water vapour and trace amounts of ammonia and methane
There is much uncertainty and debate over the exact composition – sometheories suggest it was almost all carbon dioxide, while other theoriessuggest nitrogen was also present in significant quantities
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 11/22
3800 million years ago...
H2O(l)
CO2(g)
H2O(s)
The Earth and its atmosphere cooled, and when it cooled below 100ºC thewater vapour condensed and fell as rain, forming the oceans. Icy cometsalso brought water to Earth, adding to the oceans as they melted.
Carbon dioxide in the atmosphere was able to dissolve in the oceans, forminghydrogencarbonates, which can be used to form shells of sea creatures.
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 12/22
The was little or no oxygen in the early Earth‟s atmosphere.
Scientists base their theories about what the atmosphere must have been like and
how it changed on evidence from air bubbles trapped in ancient rocks, and by
comparing with the atmospheres of other planets and moons in the Solar
System.
Venus (left) and Mars (right) both have atmospheres which scientists
believe resemble that on the Earth before life appeared
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 13/22
2200 million years ago...
Scientists think the earliest life on Earth began about 3400 million years agowhen simple organisms like bacteria appeared. They could use ammonia in
the atmosphere to make food – turning it into nitrogen (denitrifying bacteria)or nitrates in the soil (nitrifying bacteria).
About 2200 million years ago algae and bacteria became able to use energy
from the sun to photosynthesise, making foods for themselves. Oxygen began to be released into the atmosphere – a waste product of this process
6 CO2 + 6 H2O → 6 O2 + C6H12O6
carbon water oxygen sugardioxide (glucose)
Some of the earliest micro-organisms could not tolerate oxygen, and died
out.
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 14/22
1000 million years ago...
Plants of all shapes and sizes flourished, using carbon dioxide forphotosynthesis and increasing the level of oxygen in the atmosphere.Conditions on Earth were right for creatures that gathered their food from
around them and used oxygen to break it down (respiration) to produceenergy.
The amount of carbon dioxide fell to a very low level as it was trapped in thestructure of dead plant materials which were buried to form fossil fuels. Carbon dioxide also dissolved in the oceans where it was later used by seacreatures as carbonates for shells formation, ultimately forming limestone as these creatures died and their shells became part of sedimentary rocklayers.
An ammonite fossil
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 15/22
The increase in numbers and types of organisms using oxygen to respire andproducing carbon dioxide as a waste product allowed a balance to beestablished between plant life and animal life.
6 O2 + C6H12O6 → 6 CO2 + 6 H2Ooxygen sugar carbon water
(glucose) dioxide
For the last 200 million years the atmosphere has remained essentially stable.
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 16/22
This diagram
summarises the main
changes which have
taken place in the
atmosphere from the
early volcanic
atmosphere to the
beginning of the
industrial revolution
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 17/22
Nitrogen (and ammonia)
Nitrogen was probably present in the early
atmosphere, released with other gases duringvolcanic eruptions. It is also one of the two elements
present in ammonia gas, which was present in traceamounts in the early atmosphere.
There are different scientific theories about how
much nitrogen there was, but it was probably a small
amount compared to carbon dioxide.
Nitrogen levels increased in the atmosphere up to
200 million years ago, as a result of:
• denitrifying bacteria converting ammonia into nitrogen
• ammonia reacting with the oxygen formed by the
plants
4 NH3 + 3 O2 → 2 N2 + 6 H2O
N2
time
This reduced the level of poisonous ammonia gas in the atmosphere to nothing.
Bacteria &
Oxygen reacting
with ammonia
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 18/22
Oxygen
There was little or no oxygen present in the
early atmosphere.
The appearance of algae and bacteria which
could photosynthesise caused oxygen to enter
the atmosphere as a waste-product and the levelincreased.
6 CO2 + 6 H2O → C6H12O6 + 6 O2
Oxygen reacted with trace ammonia and
methane in the early atmosphere, removing
these poisonous gases
With oxygen available in the atmosphere, animal
species began to appear which could use oxygen
for respiration. This removed oxygen from the
atmosphere, balancing the production of oxygen
by plants.
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
O2
time
Photosynthesis
Balancewith
respiration
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 19/22
Carbon dioxide
The early atmosphere contained a high proportion of
carbon dioxide. There are different theories as to exactly
how much carbon dioxide there was.
Carbon dioxide levels decreased due to photosynthesis.
Plant matter became buried forming fossil fuels. Carbon
dioxide dissolved in the oceans, where sea creatures
used it to form shells. These shells later formed
sedimentary rocks.
CO2
time
Photosynthesis
Plant matter & fossil fuels
Dissolved in sea
Shells of sea creatures
Industrialisation
Trace levels of methane in the atmosphere reacted with
oxygen, producing carbon dioxide :
CH4 + 2 O2 → CO2 + 2 H2O
Carbon dioxide was also produced by animals as a waste product of respiration,
and a balance was achieved lasting 200 million years with atmospheric levels of
carbon dioxide at around 0.03%
Over the last two hundred years the industrialisation of society, based on burningfossil fuels for energy and transport, along with deforestation to clear rainforest
areas for development, have caused a rise in carbon dioxide levels to 0.04% – a
significant increase resulting in Global Warming.
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 20/22
The carbon cycle is a natural cycle in which carbon moves between the
oceans, rocks and the atmosphere. Without man‟s interference the carbon cycle
keeps on operating in balance. The oceans act as massive reservoirs for carbondioxide, dissolving excess CO2 to produce hydrogencarbonates, and releasing it
when it is in short supply. Carbon dioxide moves back into the atmosphere by a
number of routes including respiration, and the decay of dead organisms.
The carbon cycle
is the reason why
the composition of
the atmosphereremained steady
for the last 200
million years,
until burning
fossil fuels and
massive forestclearance caused
atmospheric
carbon dioxide
levels to increase.
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 21/22
Life on EarthThere are many theories as to how life first started on Earth, but nobody knows for
sure.
Amino-acids are fundamental building blocks for molecules such as proteins which
are essential to living organisms. Some scientists, such as Miller and Urey haveinvestigated how amino acids could have been formed on the early Earth.
The interaction of lightning with
hydrocarbons and ammonia (both of
which were present on the early Earth)
has been shown to produce some of
the 20 amino acids found in living
organisms.
7/30/2019 CH1 Earth and Atmosphere
http://slidepdf.com/reader/full/ch1-earth-and-atmosphere 22/22
Making use gases from the air
The mixture of gases which make up air can be separated by fractional distillation.
The air is cooled until it liquifies, then it is warmed up slowly. When each gas in theliquid air reaches its boiling point, it turns from liquid to gas, and can be collected.
The other gases are left in the liquid state until their boiling points are reached.
Recommended