Transcript Document

Earth’s Atmosphere
The earth’s crust
3 layers: Crust, mantle and core. The mantle
is mostly solid, but can move slowly
The crust is cracked into tectonic plates
How do tectonic plates move?
1. Radioactive processes occur in the core which release heat.
2. The heat travels through the mantle by convention currents.
These convection currents cause the plates to move a few cm per year
If the movements are sudden, earthquakes and/or volcanoes can occur
at the plate boundary
When plates crash into each other, it causes mountain ranges
Wegeners theory of crustal movement/ continental drift
The continents were once joined by gradually moved apart.
He thought this as there were similar fossils on continents that were
very far apart (s america and africa)
The shapes of the continents fitted
He thought that the mountain ranges on the earth’s surface were
caused by continents colliding.
Scientists did not believe him as he could not explain how they moved
What did they believe?
They believed that mountain ranges were caused by the earth’s crust
cooling and shrinking after it was first formed
They also thought there was a land bridge (which had now sunk)
between s America and Africa, which explains the fossils.
Formation of the atmosphere
The atmosphere is a layer of gases surrounding the earth. It is held in
place by gravity
During the first billions years of the earth’s existence there was
intense volcanic activity.
This released the gases which made up the atmosphere.
One theory about the atmosphere is that…
It was mostly carbon dioxide and water vapour.
There was also small amounts of ammonia or methane
There was little or no oxygen
Today’s atmosphere
The atmosphere has been the way it is today for 200 million years
It is made up of mostly nitrogen (78%).
It also contains 21% oxygen
It contains 0.04% carbon dioxide
The remainder is made up of water vapour, methane and noble gases
Uses of noble gases- Helium (balloons) Neon (advertising signs) Argon (light bulbs)
The differences between the early and today’s atmosphere
Water vapour:
There is much less water vapour now
It condensed to form the oceans
Carbon dioxide:
There is much less carbon dioxide now.
It was taken in by plants The plants died and formed layers
These eventually formed sedimentary rocks (fossil fuels)
It also dissolved in the oceans to form carbonate rocks.
Oxygen:
Produced by plants (photosynthesis)
How did life begin? The Miller Urey experiment
Amino acids are needed to make a living organism
Amino acids are made up of carbon, hydrogen, nitrogen and oxygen
Miller and Urey did an experiment to see if they could make amino acids under
conditions like the early atmosphere
They used water, ammonia methane and hydrogen.
These did not react under normal conditions
They did react when Miller and Urey used a high voltage to produce a spark. This
simulated lightening
This provided energy for the reaction
11 amino acids were formed
This provides some evidence that lightening may have provided the energy to
create life.
Primordial soup theory
Organic molecules (found in the sea) form a ‘primordial soup’
These then reacted together to form the first primitive cells
Fractional distillation of air
Fractional distillation is used to separate liquids with different boiling points.
1.
Air is cooled until it condenses to a liquid (-200 C)
2.
Carbon dioxide and water are removed from the mixture as they are solid
at this temperature.
3.
Liquid is warmed.
4.
Nitrogen is collected at the top and oxygen at the bottom
Uses of Nitrogen and Oxygen
Nitrogen:
Very unreactive so stops food going off
Used to make ammonia
Oxygen:
Helps people breathe (accident scene or in hospital)
Vegetable Oils
Plant oils
These are important foods as they provide us with a lot of energy
and nutrients
This is found in fruits, nuts and seeds
To extract the oil, you need to crush the plant material and press
the oil out
Water and other impurities are then removed
Cooking with vegetable oils
Vegetable oils have a higher b.p that water
This means they can be used to cook foods at higher temperatures
(where the water would just evaporate)
This means food can be cooked faster, and can also be flavoured
differently
However, oils release more energy when eaten, which turns to fat
if not burned.
Emulsions
Some substances do not mix. They are said to be immiscible (eg oil
and water).
We can use an emulsifier to force them to mix.
The remaining mixture is called an emulsion.
Emulsions are more viscous than oil and water
Emulsions provide better texture, coating ability and appearance
Unsaturated oils contain C=C double bonds which can be tested for
using bromine water (goes colourless as with alkenes)
We can harden unsaturated oils to increase the melting
temperature. This makes them solid as room temperature,
which makes them useful as spreads.
Hardening vegetable oils
React with hydrogen at 60 ̊C
Use a Nickel catalyst to speed up the process
The saturated oil is called a hydrogenated oil