8 & water treatment (2.9)

Question 1

Formation of the early atmosphere and oceans

Answer 1

The Earth’s surface was originally molten for many millions of years. It was so hot that any atmosphere just dispersed into space. Eventually things cooled down a bit and a thin crust formed, but volcanoes kept erupting.
There was intense volcanic activity for the first billion years after the Earth was formed, and the volcanoes gave out lots of gas. Scientists think that these gases went on to form the early atmosphere and the oceans. There are lots of different theories, but the most popular theory suggests that the early atmosphere was probably mostly carbon dioxide (CO), with little or no oxygen (O2). This is quite like the atmospheres of Mars and Venus today. Volcanic activity probably also released nitrogen, which built up in the atmosphere over time, as well as water vapour, and small amounts of methane (CH) and ammonia (NH).
As the Earth cooled, the water vapour in the atmosphere condensed, forming the oceans.

Question 2

Decreasing the amount of carbon dioxide

Answer 2

Although the early atmosphere was mostly carbon dioxide, it didn’t stay that way for long. Most of the carbon dioxide was gradually removed from the atmosphere. This happened in 2 ways.
* Absorption by the oceans
* Absorption by plants and algae

Question 3

Absorption by the oceans

Answer 3

The oceans are a natural store of carbon dioxide. When the oceans formed, a lot of the carbon dioxide from the atmosphere dissolved into them. This dissolved carbon dioxide then went through a series of reactions to form carbonate precipitates that formed sediments on the seabed. When marine animals evolved, their shells and skeletons contained carbonates from the oceans. When they died, they formed sedimentary rocks such as limestone, locking the carbon dioxide away.

Question 4

Absorption by plants and algae

Answer 4

Green plants and algae evolved over most of the Earth. Algae evolved first- about 2.7 billion years ago. Then over the next billion years or so, primitive green plants also evolved. They absorbed some of the carbon dioxide in the atmosphere and used it for a process called photosynthesis.

Question 5

photosynthesis

Answer 5

As well as absorbing the carbon dioxide in the atmosphere, green plants and algae produced oxygen by photosynthesis - this is when plants use light to convert carbon dioxide and water into:

Question 6

Increasing the amount of oxygen

Answer 6

As well as absorbing the carbon dioxide in the atmosphere, green plants and algae produced oxygen by photosynthesis.
As the oxygen level built up in the atmosphere over time, organisms that couldn’t tolerate it were killed off. The increase in oxygen allowed more complex life (like animals), that needed more oxygen, to evolve. The oxygen also created the ozone layer O3 which blocked harmful rays from the Sun and enabled even more complex organisms to evolve.
Eventually, as the levels of O2 increased and CO2 decreased, the atmosphere reached a composition similar to what it is today, with virtually no CO2 left.

Question 7

Test for oxygen

Answer 7

You can test for the presence of oxygen in the lab. To test for oxygen, put a glowing splint inside a test tube containing the gas. If oxygen is present, it will relight the glowing splint

Question 8

What is greenhouse gases?

Answer 8

Greenhouse gases, such as carbon dioxide, methane and water vapour, are present in small amounts in the Earth’s atmosphere. They act like an insulating layer, keeping the Earth warm.

Question 9

What is the greenhouse effect?

Answer 9

All particles absorb certain frequencies of radiation. The sun emits short wavelength electromagnetic radiation which passes through the Earth’s atmosphere, as it isn’t absorbed by greenhouse gases. The short wavelength radiation reaches the Earth’s surface, is absorbed, and then re-emitted as long wavelength, infrared (IR) radiation. This radiation is absorbed by greenhouse gases in the atmosphere. The greenhouse gases then re-radiate it in all directions - including back towards Earth. The IR radiation is thermal radiation, so it warms the surface of the Earth. This is the greenhouse effect.

Question 10

Human activity and greenhouse gases

Answer 10

It’s thought that human activities have caused a rise in greenhouse gas concentrations in the atmosphere. For example, the level of carbon dioxide is increasing.

Question 11

Global Warming

Answer 11

The level of carbon dioxide in the atmosphere has increased because we are adding more CO2 to the atmosphere and less is being removed from it. We are also adding to the amount of other greenhouse gases in the atmosphere, such as methane.
Increased levels of greenhouse gases in the atmosphere enhance the greenhouse effect as more IR radiation is absorbed and radiated back towards Earth, which causes the Earth to get warmer - this is global warming.

Question 12

Increasing energy consumption

Answer 12

Over the last 150 years or so, the world’s human population has shot up, and we’ve become more industrialised. Both factors mean that we’ve increased our energy consumption and are burning more up and more fossil fuels.
Examples
* An increasing global population means that more energy is needed for lighting, heating, cooking, transport and so on.
* People’s lifestyles are changing too. This means that the average energy demand I per person is also increasing (since people have more electrical gadgets and more people have cars or travel on planes, etc.)
Burning more fossil fuels means that carbon, that was ‘locked up’ in the fuels, has been released into the atmosphere in the form of CO2.

Question 13

Deforestation

Answer 13

More people also means more land is needed to build houses and grow food. We’ve been chopping down forests (known as deforestation) to create this extra space. This is a problem as plants absorb carbon dioxide by photosynthesis. So fewer plants means less carbon dioxide is being removed from the atmosphere.

Question 14

Methane and farming

Answer 14

The greenhouse gas methane is also causing problems. Like carbon dioxide, the concentration of methane has also risen a lot in recent years due to increased human activity. For example, in livestock farming, cows produce large amounts of methane. Paddy fields, in which rice is grown, produce a fair bit too. So, the larger the population gets, the more we need to farm to produce food, and the more methane is produced.
Though it’s currently only present in tiny amounts in our atmosphere, the increasing concentration of methane is an issue as it’s a highly effective greenhouse gas,

Question 15

Carbon dioxide and global warming

Answer 15

Historically, temperature change at the Earth’s surface is correlated to the level of carbon dioxide in the atmosphere. Recently, the average temperature at the Earth’s surface has been increasing as the level of carbon dioxide has increased.
Even though the Earth’s temperature varies naturally, most scientists agree that the extra greenhouse gases from human activity (mainly through burning fossil fuels) are causing an increase in temperature. This temperature increase is known as global warming and is a type of climate change. Global warming could even lead to further climate change - which may have lots of effects with negative consequences.

Question 16

Examples of negative consequences of global warming

Answer 16

• An increase in global temperature could lead to polar ice caps and glaciers melting, causing a rise in sea levels, increased flooding in coastal areas and coastal erosion.
• Changes in rainfall patterns (the amount, timing, and distribution) may cause some regions to get too much or too little water. This, along with changes in temperature, may affect the ability of certain regions to produce food.
• The frequency and severity of storms may also increase.
• Changes in temperature and the amount of water available in a habitat may affect wild species, leading to differences in their distribution.

Question 17

Challenges in obtaining climate change data.

Answer 17

The current average global temperature and carbon dioxide level can be worked out pretty accurately, as they’re based on measurements taken all over the world. Historical data is less accurate - less data was taken over fewer locations and the methods used to collect the data were less accurate. If you go back far enough, there are no records of the global temperature and carbon dioxide level at all.
But there are ways to estimate past data. For example, you can analyse fossils, tree rings or gas bubbles trapped in ice sheets to estimate past levels of atmospheric carbon dioxide. The problem with using these kinds of measurements is that they’re much less precise than current measurements made using instrumental sampling. Another issue with measuring carbon dioxide level is the location of sampling. Different areas may have varying carbon dioxide levels and may be unrepresentative of the global level.

Question 18

Mitigating the effects of climate change

Answer 18

To slow down or mitigate climate change, we need to cut down on the amount of greenhouse gases we’re releasing into the atmosphere. To reduce carbon dioxide emissions, we can try to limit our use of fossil fuels. This could be doing things on a personal level, like walking or cycling instead of driving or turning your central heating down.
On a larger scale, the UK government has formed plans to encourage the public and industry to become more energy efficient, to create financial incentives to reduce CO2 emissions, to use more renewable energy and to increase research into new energy sources.
Technology could also be used to reduce some of the effects of climate change. For example, flood defences can be used which could keep homes safe from flooding. However, the long-term effects of climate change are hard to predict, and new technology may have knock-on environmental implications.

Question 19

Sources of water

Answer 19

In the UK, there are a number of sources of water which can be purified provide us with potable water (water that is fit to drink). The main sources of water in the UK are:
* Surface water: from lakes, rivers, and reservoirs. In much of England and Wales, these sources start to run dry during the summer months.
* Ground water: from aquifers (rocks that trap water underground). In parts of south-east England, where surface water is very limited, as much as 70% of the domestic water supply comes from ground water.
* Wastewater: from water that’s been contaminated by a human process, e.g., as a by-product from some industrial processes. Treating wastewater is often better for the environment than simply disposing of it, as wastewater can contain pollutants. How easy wastewater is to treat depends on the levels of contaminants in it.

Question 20

Water purification

Answer 20

Water from some sources is dirtier than from others, and so requires a lot more treatment to make it drinkable. Ground water from aquifers is normally quite clean, but wastewater and surface water need far more treatment.

Question 21

The process of purification

Answer 21

No matter the source, all water must go through a basic process of purification to make it potable. This process includes:
1. Filtration - a wire mesh screens out large twigs, etc., and then gravel and sand beds filter out any solid bits.
2. Sedimentation iron sulphate or aluminium sulphate is added to the water, which makes fine particles clump together and settle at the bottom.
3. Chlorination - chlorine gas is bubbled through to kill harmful bacteria and other microbes.

Question 22

Distilling sea water

Answer 22

In some dry countries, e.g., Kuwait, there’s not enough surface water or ground water, so instead sea water must be distilled to provide potable water. The sea water is boiled to produce steam, which is then condensed - this separates the water from the dissolved salts.
Distillation requires a lot of energy, so it’s really expensive, especially if it’s used to produce large quantities of fresh water. Countries don’t tend to use this if there are other sources of water available.

Question 23

Deionised water

Answer 23

A lot of analytical chemistry involves carrying out experiments to work out what something is, or how a substance will react. For experiments that involve mixing or dissolving something in water, you should use something called deionised water.
Deionised water is water that has had the ions (such as calcium, iron, and copper ions) that are present in normal tap water removed. These ions, although present in small amounts and harmless in tap water, can interfere with reactions. So, using normal water could give your experiment a false result.