CH1 Earth and Atmosphere

7/30/2019 CH1 Earth and Atmosphere

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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



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.



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.



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.



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



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



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

http://www.volcanolive.com/






Nitrogen

OxygenNoble Gases

Carbon dioxide

78%

21%

0.9% 0.04% The Atmosphere



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...



H2O(g)

CO2 trace

NH3 trace

CH4


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




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.



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




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.




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



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.



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



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



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



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.

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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.



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.



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.

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CH1 Earth and Atmosphere