The Structure of the Earth
The Earth has a layered structure including the core, mantle and crust. The crust and upper mantle are cracked into large peices called tectonic plates. These plates move slowly but can cause earthquakes and volcanoes where they meet.
The earths crust, its astmosphere and oceans are the only sources of the resources that humans need.
The earth is almost a sphere. There are its main layers, starting with the outermost
- Crust (relatively thin and rocky)
- Mantle (has the properties of a solid, but can flow very slowly
- Core (made from liquid nickel and iron)
The radius of the core is just over half the radius of the earth. The core itself consists of a solid inner core an a liquid outer core. The earths atomostphere surrounds the earth.
The earths crust and upper part of the mantle are broken into large peices called tectonic plates. These are constantly moving at a few centimetres each year. Over millions of years the movement allows whole continents to shift thousands of kilometres apart. This process is called continental drift.
- The plates move because of covection currents in the earths mantle.
- These are driven by the heat produced by the natural decay of radiocactive elements in the earth .
- Where tectonic plates meet, the earths crust becomes unstable as the plates push against each other, or ride under or over each nother.
- Earthquakes and volcanic erruptions happen at the boundries between plates, and the crust may 'crumble' to form mountain ranges.
- It is difficult to predict exactly when an earthquake might happen and how bad it will be, even in places known for having earthquakes.
- The theory of plate tectonics and continental drift was proposed at the beginning of the last century by a german scientist, Alfred Wegener.
- Before Wegener developed his theory, it was thought that mountains formed because the earth was cooling down, and in doing so contracted
- This was believed to form wrinkles, or mountains in the earths crust
- If this idea was correct, mountains would be spread evenly over the earths surface
- Wegener suggested that mountains were formed when the edge of a drifiting continent collided with another, causing it to crumble and fold.
- For example, the himalayas were formed when India came into contact with Asia.
- It took more than 50 years for Wegeners theory to be accepted.
- One of the reasons that is was difficult to work out how whole continents could move: It was not until the 1960s that enough evidence was discovered to support the theory fully
Volcanoes and Earthquakes
- Two types of Tectonic Plates
- Oceanic plates occur under the oceans
- Continental plates form the land
- Oceanic plates are denser than continental plates. They are pushed down underneath continental plates if they meet
- Where tectonic plates meet, the earths crust becomes unstable as the plates slide past eachother, push against eachother or ride under or over one another.
- Earthquakes and volcanic eruptions happen at the boundries between plates.
- Magma (Molten rock) is less dense than the crust. It can rise to the surgace through weaknesses in the crust forming a volcano
- Geologists study volcanoes to try to predict future eruptions.
- Volcanoes can be very destructive, but some people choose to live near them because volanic soil is very fertile
The movement of tectonic plates can be sudden and disastrous, causing an earth quake. Difficult to predict when and where an earthquake will happen.
Energy Transfer by Heating
- Heat can be transferred from place to place by conduction, convection and radiation.
- Dark matt surfaces are better at absorbing heat energy than light shiny surfaces.
- Heat energy can be lost from homes in many different ways and there are ways of reducing these heat losses.
The Modern Atomsphere
The earths atmosphere has remained much the same for the past 200 million years.
- The two main gases are both eleemtns and account for about 99 percent of the gases in the atmosphere.
- About 4/5 or 80% nitrogen (a relatively unreactive gas)
- About 1/5 or 20% oxygen (the gas allows and animals and plants to respire and for fuels to burn)
- The remaining gases, such as carbon dioxide, water vapour and noble gases such as argon are found in much smaller proportions
Oxygen in the Air
The percentage of oxygen in the air can be measrued by pasing a known volume of air over hot copper and measuring the decrease in volume as the oxygen reacts with it/
- copper + oxygen > copper oxide
- 2Cu +O2 > 2CuO
Gas syringes are used to measure the volume of gas in the experiment. The starting volume of air used is often 100cm3 to make the analysis of the results easy, but it could any convinent volume.
Note that there is some ait in the tube with the copper turnings. The oxygen in this air will also react with hot copper, causing a small error in the final volume recorded. It is also important to let the appartatus cool down at the end of the experiment otherwise the final reading will be to high
The Early Atmosphere
Scientists believe that the earth was formed about 4.5 billion years ago. Its early atmosphere was probably formed from the gases given out my volcanoes. It is believed that there was intense volcanic activity for the first billion years of the earths existense.
The early atmosphere was proably mostly cabron 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.
Mars and Venus today
It is thought that the atmosphere of Mars and Venus today, which contain mostly carbon dioxide, are similar to the early atmosphere of the earth.
- Carbon Dixiode - 95.3 96.5
- Nitrogen - 2.7 3.5
- Argon- 1.6 Trace
- Oxygen, water vapour and other gases - Trace Trace
- Green = Venus
- Red = Mars
Life on Earth
There is evidence that the first living things appeared on Earth billions of years ago. There are many scientific theoryies to explain how life began. One theory involves the interaction between hydrocarbons, ammonia and lightning.
The Miller-Urey experiment
Stanley Miller and Harold Urey carried out some experiments in 1952 and published their results in 1953. The aim was to see if substances now made by living things could be formed in the conditions thought ot have existed on the early earth.
- Two scientists sealed a mixture of water, ammonia, methane and hydrogen in a sterile flask.
- The mixture was heated to evaporate water to produce water vapour.
- Electric sparks were passed through the mixture of water vapour and gases, simulaiting lightning
- After a week, contents were analysed
- Amino acids, the building blocks for protiens were found
- The Miller-Urey experiment supported the theory of a 'primordial soup', the idea that complex chemicals needed for living things to develop could be produced naturally on the early earth
Oxygen and Carbon Dioxide
The earths early atmosphere is believed to have been mainly carbon dioxide with little or no oxygen gas. The earths atmophsere today contains around 21% oxygen and 0.04% carbon dioxide. SO how did the proportion of cabron dioxide in the atmosphere go down, and the proportion of oxugen go up?
Plants and algae carry out photosynthesis. This process used cabron dioxide from the atmosphere (with water and sunlight) to produce oxygen (and glucose). The appearance of plants and algae caused the production of oxygen, which is why the proportion of oxygen went up.
Decreasing carbon dioxide
Photosynthesis by plants and algae used carbon dioxide from the atmosphere, but this is not the only reason why the proportion of carbon dioxide went down.
- Dissolving in the oceans
- The production of sedimentary rocks such as limestone
- The production of fossil fuels from the remains of dead plants and animals
Oxygen and Carbon Dioxide 2
Today, the burning of fossil fuels (coal and oil) is adding carbon dioxide to the atmosphere faster than it can be removed.
This means that the level of carbon dioxide in the atmosphere is increasing, contributing to global warming. It also means that the oceans are becoming more acidic as they dissolve increaing amounts of carbon dioxide. This has an impact of the marine environment, for example making the shells of sea creatures thinner than normal
Fractional distillation of liquid air
78% of the air is nitrogen and 21% is oxygen. These two gases can be seperated by fractional distillation of liquid air.
Liquefying the air
Air is filtered to remove dust, and then cooled in stages until it resched -200 degrees. At this temperature it is a liquid. Liquefied.
The liquefied air is passed into the bottom of a fractionating column. Just as in the columns used to seperate oil frations, the column is warmer at the bottom than it is at the top.
- The liquid nitrogen boils at the bottom of the column.
- Gaseous nitrogen rises to the top, which it is piped off and stored.
- Liquid oxygen collects at the bottom of the column the boiling point of argon- the noble gas that forms 0.9% of air- is close to the boiling point of oxygen so a second fractionating column is often used to seperate argon from the oxygen
Fractional distillation of liquid air 2
Uses of Nitrogen and Oxygen
- Liquid nitrogen is used to freeze food
- Food is packaged in gaseous nitrogen to increase its shelf life
- Oil tankers are flushed with gaseous nitrogen to reduce the chance of explosion
- Oxygen is used in the manufature of steel and in medicine