oil, plasticqwertys & the earth key notes

7/29/2019 Oil, Plasticqwertys & the Earth Key Notes

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Oil, Plastics & The Earth Key Notes

Fossil fuels formed millions of years ago from the remains of living things (coal

from plants and natural gas and oil from sea creatures) - they were gradually

buried by layers of rock which stopped them rotting

The buried remains were put under pressure and chemical reactions heated them

up, gradually changing into fossil fuels

Some oil and natural gas was covered by cap rock which is impermeable (not letting

them through)

They can be removed from the ground by drilling through the rock

Crude oil is a mixture of compounds called hydrocarbons they only containhydrogen and carbon atoms, joined together by chemical bonds

There are different types of hydrocarbon, but most of the ones in crude oil are

alkanes

The alkanes are a family of hydrocarbons that share the same general formula: -

CnH2n+2

The general formula means that the number of hydrogen atoms in an alkane is

double the number of carbon atoms, plus two

E.g. methane is CH4 and ethane is C2H6


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Alkane molecules can be represented by displayed formulae in which each atom is

shown as its symbol (C or H) and the chemical bonds between them by a straight

line

As the alkane chain increases in length the properties change longer chains meanthe following: -

Less ability to flow (more viscous)

Less flammable

Less volatile

Increased boiling points

Alkanes are saturated hydrocarbons this means that their carbon atoms are

joined to each other by single bonds

This makes them relatively un-reactive, apart from their reaction with oxygen in

the air during combustion (they do burn well)!


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Hydrocarbons have different boiling points, and can be either solid, liquid or gas at

room temperature: -

Small hydrocarbons with only a few carbon atoms have low boiling points and

are gases

Hydrocarbons with between 5 and 12 carbon atoms have medium boiling

points and are usually liquids

Large hydrocarbons with many carbon atoms have high boiling points and are

solids

Some of the 21st centurys most important chemistry involves chemicals that are

made from crude oil they are used for fuels in cars; warming of homes; making

electricity etc When oil prices rise it affects us all countries that produce

crude oil can have an affect on the world economy by the price charged for oil

Crude oil originates as a dark, smelly liquid which is a mixture of lots of different

chemical compounds it is not much use straight out of the ground (there are too

many substances in it, all with different boiling points). As such it needs to be

refined

Although we can get useful substances from oil, crude oil itself has no uses. In

order to make crude oil into useful substances we first have to separate the

mixture into molecules of similar size this is done in an oil refinery

Crude Crude oil is a mixture of different sized hydrocarbons the exact

composition depends upon where the oil comes from but typically it contains a lot

of big molecules


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Distillation is a process that can be used to separate a pure liquid from a mixture

of liquids it works when the liquids have different boiling points

Fractional distillation differs from distillation only in that it separates a mixture

into a number of different parts, called fractions

A tall column is fitted above the mixture, with several condensers coming off at

different heights

The column is hot at the bottom and cool at the top substances with high boiling

points condense at the bottom and substances with low boiling points condense at

the top

Like distillation, fractional distillation works because the different substances in

the mixture have different boiling points

The main fractions include refinery gases, gasoline (petrol), naphtha, kerosene,

diesel oil, fuel oil, and a residue that contains bitumen

These fractions are mainly used as fuels, although they do have other uses too


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Hydrocarbons with small molecules make better fuels than hydrocarbons with large

molecules because they are volatile, flow easily and are easily ignited

In order for it to be useful to us, crude oil is broken down in oil refineries into its

component parts (fractions), which can then be used for many different purposes

Fractions that are produced by the distillation of crude oil can go through a

process called cracking, producing smaller hydrocarbons

Crude oil often contains too many large hydrocarbon molecules and not enough

small hydrocarbon molecules to meet demand - this is where cracking comes in

Fuels made from oil mixtures containing large hydrocarbon molecules are not

efficient (they do not flow easily and are difficult to ignite)

Cracking is an example of a thermal decomposition reaction

Shorter chain hydrocarbons are in greater demand because they burn easier, and

they can be made from long chain hydrocarbons via cracking


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The products of cracking include alkenes (for example ethene and propene)

The alkenes are a family of hydrocarbons that share the same general formula: -

CnH2n

The general formula means that the number of hydrogen atoms in an alkene is

double the number of carbon atoms, e.g. ethene is C2H4 and propene is C3H6

Alkene molecules can be represented by displayed formulae, in which each atom is

shown as its symbol (C or H) and the chemical bonds between them by a straight

line

Alkenes are unsaturated hydrocarbons they contain a double bond, which is shown

as two lines between two of the carbon atoms

The presence of this double bond allows alkenes to react in ways that alkanes

cannot (they can react with oxygen in the air, so they could be used as fuels)

They can be used to make ethanol (alcohol) and polymers (plastics): two crucial

products in today's world


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Alkanes are saturated every carbon atom has already used all four of its bonds

to join to four other atoms: no other atoms can be added (it is full up)

Alkenes are unsaturated have a double bond that could instead become two single

bonds: this means that other atoms can be added

Alkanes and alkenes can be distinguished between due to this double bond

When bromine water is added to an alkane nothing happens

When bromine is added to an alkene the red colour of the bromine disappears


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Plastics are polymers (huge molecules which are made up of lots of smaller

molecules (monomers) which have been joined together)

Different types of plastics can be made by using different monomers these

plastics can have very different properties

Nylon was the first commercially successful synthetic polymer a thermoplastic

(softens when heated) silky material originally used in toothbrushes and later as

tights

Alkenes can be used to make polymers polymers are very large molecules made

when many smaller molecules join together, end-to-end

The smaller molecules are called monomers

Polymer: Poly(ethene) - polythene

Many ethene monomers can join end-to-end to make poly(ethene) or polythene

Initially the C=C double bond of the ethene must be broken, and then the molecules

can be added together


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Different polymers can be made by using different monomers these polymers can

have very different properties

Polymers have properties that depend on the chemicals they are made from, and

the conditions in which they are made polymers have many uses, including: - Waterproof coatings

Fillings for teeth

Dressings for cuts

Hydrogels for making soft contact lenses and disposable nappy liners

Shape memory polymers for shrink-wrap packaging

One of the useful properties of polymers is that they are unreactive, so they are

suitable for storing food and chemicals safely, but this property makes it difficultto dispose of polymers

Most polymers, including poly(ethene) and poly(propene) are not biodegradable

meaning that micro-organisms cannot break them down, so they may last for many

years in rubbish dumps

However, it is possible to include chemicals that cause the polymer to break down

more quickly carrier bags and refuse bags made from such degradable polymersare already available

Polymers can be burnt or incinerated they release a lot of heat energy when they

burn and this can be used to heat homes or to generate electricity


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There are problems with incineration as carbon dioxide is produced, which adds to

global warming

Toxic gases are produced unless the polymers are incinerated at high temperatures

Many polymers can be recycled reducing the disposal problems and the amount of

crude oil used

It is crucial different polymers are separated from each other first, and this can

be difficult and expensive to do

Many polymers can be recycled reducing the disposal problems and the amount of

crude oil used

Some modern plastic bags are now being made from biodegradable polymers such

as cornstarch which will increasingly provide useful replacements for the main

polymers currently used

Ethanol is the type of alcohol found in alcoholic drinks such as wine and beer

Ethanol is also useful as a fuel for use in cars and other vehicles, it is usually

mixed with petrol

Ethanol can be manufactured by reacting ethene (from cracking crude oil) with

steam phosphoric acid is used as a catalyst: -

Ethene + Steam Ethanol


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C2H4+ H2O C2H5OH

In the reaction ethanol is the only product the process is continuous as long as

ethene and steam are fed into one end of the reaction vessel, ethanol will be

produced

These features make it an efficient process, but as ethene is made from crude oil,

which is a non-renewable resource, it cannot be replaced once it is used up and it

will run out one day

Ethanol can also be made via fermentation sugar from plant material is converted

into ethanol and carbon dioxide

Enzymes found in single-celled fungi (yeast) are the natural catalysts that can

make this process happen (this is a renewable resource): -

C6H12O6 2C2H5OH + 2CO2

It is possible to make fuel for vehicles using vegetable oils biodieselis the name

given to any fuel made from vegetable oils (and they can be added to any diesel

engine)

Biodiesel is made by treating vegetable oils to remove some unwanted chemical

during production other useful products form, including a solid waste material

which can be used as cattle feed and glycerine (used in soap manufacture)

Biodiesel is a very clean fuel it also breaks down about five times faster than

conventional crude oil diesel, advantageous if spilt

It also burns much more cleanly, making far less sulfur dioxide and other pollutants

It also has a major atmospheric advantage as crops are used to make the fuel it

is carbon neutral (all the carbon released by the fuel burning was originally

absorbed by the plant from the atmosphere in the first place)


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Biodiesel therefore makes little contribution to the greenhouse gases in the

atmosphere

Biodiesel is however not without is problems: -

There are costs related to its production machinery which harvests this biodiesel

requires fuel itself, so this counts to the atmospheric cost

It also requires crops ethical issues arise over using crops for fuel when famine is

still widespread throughout the world

There is also a great amount of financial reward to producing biodiesel areas of

tropical rainforest are being cleared in huge amounts to grow this money-making

crop, leaving vast areas having their natural flora and fauna destroyed forever

Combustion is the chemical reaction which takes place when a substance burns

The substance reacts with oxygen, releasing energy (heat and light)

Combustion is extremely important (>90% of the worlds energy comes from

combustion reactions (e.g. fossil fuels such as coal, natural gas and petrol)

Combustion is exothermic - heat is released to the surroundings

This can also be called an oxidationreaction, as it involves oxygen being added to

the fuel the carbon and hydrogen in the fuels are oxidised

The fuel you use will result in different combustionreactions taking place

A good supply of oxygen is needed for a fuel to burn completely and release as

much energy as possible


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If there is a plentiful supply of oxygen we get complete combustion

However, if there is not enough oxygen then the fuel will not burn completely,

wasting both the fuel and reducing the energy released

If there is not enough oxygen we get incomplete combustion

Complete combustion: -

carbon + oxygen carbon dioxide

Incomplete combustion: -

carbon + oxygen carbon monoxide

Levels of carbon dioxide in the atmosphere are increasing in no small part due to

the increased burning of fossil fuels

As carbon dioxide levels in the atmosphere increase so the reaction between

carbon dioxide and seawater increases producing insoluble carbonates and soluble

hydrogen-carbonates

In this way the sea acts as a buffer however this buffering system is put under

increasing strain as we burn more fossil fuels


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Normally the Earth absorbs heat and emits heat at the same rate, causing the

temperature to remain constant

Certain gases, like CO2 and methane, act like a greenhouse they let heat in but do

not let it out meaning the more CO2 and methane there is, the hotter planet will

become

Acid rain has a higher than normal acid level (a low pH)

Acid rain may contain weak solutions of carbonic, sulfuric acid, and nitric acids

Where it falls over a prolonged period it can cause damage to the environment

Global dimming is also a major concern due to the burning of hydrocarbons - tiny

particles that are released when fuels are burned cause global dimming (like global

warming, this process may change rainfall patterns around the world)

The amount of sunlight reaching the Earths surface has decreased by about 2%

every ten years, because more sunlight is being reflected back into space theparticles from burning fuels reflect sunlight, and they also cause more water

droplets to form in the clouds

This makes the clouds better at reflecting sunlight back into space


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One impact of burning fossil fuels is that the products of combustion can be very

harmful to the environment

Sulfur dioxide and carbon dioxide are the two biggest gases which cause

environmental problems, as well as carbon monoxide and the oxides of nitrogen

Sulfur can be removed from fuels before they are burnt, such as the fuels used

for most vehicles

Sulfur dioxide can also be removed from the waste gases after combustion, both in

factories and vehicles (using a catalytic converter)

Car exhaust systems have catalytic converters these convert carbon monoxide

into carbon dioxide

Carbon Monoxide + Nitrogen Oxide Nitrogen + Carbon Dioxide

2CO + 2NO N2 + 2CO2

Catalytic converters also convert nitrogen oxides into nitrogen and oxygen as well

as complete the oxidation of un-burnt hydrocarbons to carbon dioxide and water

Nitrogen Oxides Nitrogen + Oxygen

Hydrocarbon + Oxygen Carbon Dioxide + Water

There are a variety of alternatives to fossil fuels, and one of the most promising is

using hydrogen as a fuel

Hydrogen and oxygen will react together releasing energy their only by-product

being water

The problem at the moment is getting the hydrogen it can be split from water,

but requires energy to do so (currently from burning fossil fuels)!


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Biofuels such as biodiesels and ethanol are produced from plant material however

is it right to grow crop for fuel when many of the worlds population remain hungry?

There are a variety of alternatives to fossil fuels, and one of the most promising is

using hydrogen as a fuel

Hydrogen and oxygen will react together releasing energy their only by-product

being water the problem at the moment is getting the hydrogen it can be split

from water, but requires energy to do so (currently from burning fossil fuels)!

Biofuels such as biodiesels and ethanol are produced from plant material however

is it right to grow crop for fuel when many of the worlds population remain hungry?

Plant oil extraction is relatively simple, involving two steps: -

Crush the plant

Remove the oil by pressing or via distillation

Molecules of vegetable oils consist of glycerol and fatty acids: -

Glycerol has three carbon atoms

Fatty acids have long chains of carbon atoms

Three long chains of carbon atoms are attached to a glycerol molecule (with its

three carbon atoms) together they combine to make one molecule of vegetable

oil


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Thee long fatty acid chains stop vegetable oils dissolving in water

The fatty acids in some vegetable oils are saturated, and only have single bonds

between their carbon atoms

Saturated oils tend to be solid at room temperature, and are sometimes calledvegetable fats instead of oils lard is an example of a saturated oil

The fatty acids in some vegetable oils are unsaturated, and have double bonds

between some of their carbon atoms

Unsaturated oils tend to be liquid at room temperature, and are useful for frying

food they can be divided into two categories: -

Monounsaturated fats have one double bond in each fatty acid Polyunsaturated fats have many double bonds

The carbon-carbon double bonds in unsaturated oils can be detected using the

elements bromine or iodine these elements react with the double bonds in the

oils, and the more double bonds there are, the more bromine or iodine is used up

Unsaturated fats can be tested for using a simple test with bromine water

bromine water is a dilute solution of bromine, which is normally orange-brown incolour which becomes colourless when shaken with an alkene, or with unsaturated

fats

When shaken with alkanes or saturated fats, its colour remains the same


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During hydrogenation, vegetable oils are hardened by reacting them with hydrogen

gas at about 60C (this increases their melting point) a nickel catalyst is used to

speed up the reaction the double bonds are converted to single bonds by the

hydrogenation

This causes unsaturated fats to be made into saturated fats

Saturated vegetable oils are solid at room temperature, and have a higher melting

point than unsaturated oils

This makes them suitable for making margarine, or for commercial use in the

making of cakes and pastry

The temperature that a liquid boils at depends on the size of the forces between

its molecules the bigger these forces the higher the liquids boiling point

The molecules in vegetable oils are much bigger than water molecules (so their

boiling point is much higher)

Cooking food causes permanent changes to occur to the food cooking in vegetable

oils causes different reactions to the food as the temperature is so much higher

(often the food cooks more quickly, turns a different colour on the outside and

becomes crisper)

Also cooking in oil can cause the food to absorb some of that oil meaning the

energy content of the food is much higher (one reason why fried food can be bad

for you)!


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Vegetable oils are important nutrients and provide a lot of energy.

Vegetable oils are also used as fuels for vehicles (some of this biodiesel is made

from waste cooking oil and rapeseed oil with benefits as these fuels are carbon

neutral)

It can be questioned how ethical it is to use food crops in this way, instead of using

them for feed when famine is still a global problem

Vegetable oils do not dissolve in water if a mixture of oil and water is shaken,

then left to stand, eventually a layer of oil will form on the surface of the water

Emulsifiers can be added to the oil and water, causing an emulsion to form (a

mixture of the two)

Emulsions are more viscous than oil or water on their own, and contain tiny droplets

of one of the liquids spread through the other liquid

Immiscible liquids do not mix together, e.g. oil floats on the surface of the water

when mixed.

If you shake oil and water together then leave them to stand, tiny droplets of oil

float upwards they join together until eventually the oil is floating on the water

again


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This is not a useful property when concerned with foods which often contain both

oil and water (such as salad cream) without a binder to hold the two together

they would keep separating

Emulsifiers are molecules that have two different ends:

A hydrophilic end (water-loving) that forms chemical bonds with water but

not with oils

A hydrophobic end (water-hating) that forms chemical bonds with oils but

not with water

The hydrophilic 'head' dissolves in the water and the hydrophobic 'tail' dissolves

in the oil

In this way, the water and oil droplets become unable to separate out the

mixture formed is called an emulsion

An emulsion is a mixture of oil and water

An emulsifier is a specific molecule able to bind the two ends so they stick

together (i.e. the oil and water bind)

E.g. Lecithin is an emulsifier which binds the emulsion of water and oil


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Emulsions are thicker than oil or water and have many uses that depend on their

special properties

Emulsions can provide better texture or coating ability and appearance

Examples of oil droplets in water: -

Egg yolk

Milk

Ice cream

Salad cream

Mayonnaise

Examples of water droplets in oil: -

Margarine

Butter

Skin cream

Moisturising lotion

Partially hydrogenated vegetable oils may contain trans fats these are thought to

cause health problems such as heart disease in humans, and food manufacturers

are being encouraged to reduce the amount of them in our food

The Earth is almost a sphere, consisting of four main layers

Crust relatively thin and rocky

Mantle has the properties of a solid, but can flow very slowly

Outer core made from liquid nickel and iron

Inner core made from solid nickel and iron

The average density of the Earth is much higher than the crust, meaning the inner

core must be very dense solid nickel and iron


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Why does the Earth look the way it does has it always looked this way and will it

remain?

The Earth's crust and upper part of the mantle are broken into large pieces called

tectonic plates these are constantly moving at a few centimetres each year

Although this rate is not great, over millions of years the movement allows whole

continents to shift thousands of kilometres apart called continental drift

The plates move because of convection currents in the Earth's mantle, driven by

the heat produced by the decay of radioactive elements and heat left over from

the formation of the Earth

Where tectonic plates meet, the Earth's crust becomes unstable as the plates

push against each other, or ride under or over each other

Earthquakes and volcanic eruptions happen at the boundaries between plates, and

the crust may crumple to form mountain ranges

The theory of plate tectonics and continental drift were proposed at the beginning

of the last century by a German scientist, Alfred Wegener

Before his time it was believed that the planet's features, such as mountains, were

caused by the crust shrinking as the Earth cooled after it was formed


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It took more than 50 years for Wegeners theory to be accepted because it was

difficult to work out what the mechanism was that could make whole continents

move, and it was not until the 1960s that enough evidence was discovered to

support the theory fully

Alfred Wegener suggested that the continents looked like they fit together

He also noted they have similar rock patterns and fossil records these two pieces

of evidence led him to believe that there was once a single land mass, and form the

tectonic theory

The massive amounts of heat generated through radioactive decay in the core

power convection currents in the mantle causing the crust to move, as well as the

spreading of the sea floor at plate boundaries as new crust is formed both key

discoveries and proof of Wegeners theory

Plate tectonics explained why earthquakes and volcanoes were concentrated in

specific places - around the boundaries of moving plates


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The match in shape between the east coast of South America and the west coast

of Africa suggests both were once part of a single continent

There are similar patterns of rocks and similar fossils on both sides of the

Atlantic - including the fossil remains of land animals that would have been unable

to swim across an ocean

The Earth was formed about 4.5 billion years ago its early atmosphere was

probably formed from the gases given out by volcanoes

It is believed that there was intense volcanic activity for the first billion years of

the Earth's existence the early atmosphere was probably mostly carbon dioxide,

with little or no oxygen

There were smaller proportions of water vapour, ammonia and methane

As the Earth cooled down, most of the water vapour condensed and formed the

oceans

It is thought that the atmospheres of Mars and Venus today, which contain mostly

carbon dioxide, are similar to the early atmosphere of the Earth

The proportion of oxygen went up because of photosynthesis by plants


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The proportion of carbon dioxide went down because: -

It was locked up in sedimentary rocks, such as limestone, and in fossil fuels

It was absorbed by plants for photosynthesis

It dissolved in the oceans

The burning of fossil fuels is adding carbon dioxide to the atmosphere

faster than it can be removed meaning the level of carbon dioxide in the

atmosphere is increasing

As oxygen levels rose atmospheric ammonia (NH3) reacted with oxygen (O2) to

form water (H2O) and nitrogen (N2)

Also, living organisms, including denitrifying bacteria, broke down nitrogen

compounds releasing more nitrogen into the atmosphere

And so the atmosphere headed towards a composition that has remained fairly

constant for the last 200 million years

Oxygen normally exists as pairs of atoms (O2)

Oxygen can, however, turn into another form that has three atoms joined

together: this is ozone (O3) as oxygen levels rose, so did the amount of ozone

This layer of ozone in the atmosphere filters out harmful ultraviolet rays from the

sun this will have allowed new organisms to evolve and survive


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The Earth's atmosphere has remained much the same for the past 200 million

years

The main gas is nitrogen and oxygen (the gas that allows animals and plants to

respire and fuels to burn) is the next most abundant gas

These two gases are both elements and account for about 99% of the gases in the

atmosphere the remaining gases, such as carbon dioxide, water vapour and noble

gases such as argon, are found in much smaller proportions

The early Earth was very different to the one we know today it was hotter and

the atmosphere consisted mostly of carbon dioxide, with other gases such as

ammonia and methane


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There are two possible origins for these molecules: -

They were produced by the conditions on Earth at the time, or

They came from somewhere else, such as another planet in our solar system

or further out in space

Over many millions of years these molecules joined with other molecules, becoming

gradually more complex and dependent on each other

The process of evolution by natural selection eventually led to all of the different

living things that we see on Earth today

Sometime between about 4.1 billion years ago when the Earths crust began to

solidify, and 3.5 billion years ago life began

Most biologists subscribe to the hypothesis that life developed on Earth from non-

living materials that became ordered into molecular aggregates these eventually

became capable to self-replication and metabolism

In the ancient environment the origin of life was evidently possible (conditions

were very different, with more intense lightning; volcanic activity; meteorite

bombardment; and UV radiation)

One hypothesis suggests the first organisms were products of a chemical evolution

in four stages: -

1. The abiotic (non-living) synthesis and accumulation of small organic

monomers such as amino acids and nucleotides from a primordial soup

2. The joining of these monomers into polymers (including proteins and nucleic

acids)

3. The aggregation of abiotically produced molecules into droplets

(protobionts) with chemical characteristics different from their

surroundings

4. The origin of heredity


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It is not possible to be certain how life on Earth began because: -

Earth is about 4,500 million years old

There is evidence living things existed on Earth at least 3,500 million years

ago

No-one was there to record how life began

The best we can do is study simple organisms and the chemistry of living things to

work out scientific theories

The main theory is that living things developed from molecules that could copy

themselves, rather as DNA does

It is not known how life began on the Earth because there is not enough evidence

available

An experiment by Miller and Urey in 1952 tried to recreate the conditions which

may have been present in the Earths atmosphere around 3 billion years ago

They used a sealed and sterile glass flask with the gases ammonia, methane,

hydrogen and water vapour inside they then passed electrical sparks (simulating

lightning) through the gases for a week

When they analysed the mixture they found many carbon compounds had formed

inside the flask (from the methane gas)


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Some of these compounds were found to be amino acids (used to make proteins)

This suggests the first life forms may have been bacteria able to utilise the

methane and ammonia to live

oil, plasticqwertys & the earth key notes

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