KS4 Chemistry

1. KS4 Chemistry Earth and Atmosphere

2. Contents Earth and Atmosphere Development of the atmosphere O3 and CO2 The Earth’s structure Plate tectonics Rocks Summary activities

3. The Earth was formed about 4,500 million years ago. During the first billion years there was intense volcanic activity, which produced the early atmosphere. This would have contained large quantities of carbon dioxide (CO2) and water vapour. Methane (CH4) and ammonia (NH3) are thought to have also been present. This is rather like the atmosphere on Mars and Venus today. The water vapour condensed to form the oceans. Mars Venus The early atmosphere

4. Carbon dioxide reacted with rocks and much became trapped in them. The evolution of algae some 3,000 million years ago, and subsequently plants which successfully colonized the Earth’s surface, led us towards the present atmosphere. Their photosynthesis replaced carbon dioxide with oxygen. Over a period of time, billions of tonnes of carbon dioxide became locked up in fossil fuels. Earth Photosynthesis increased oxygen levels Oxygen levels increase

5. 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. 1% 21% Nitrogen Oxygen Other 78% Nitrogen appears

6. Copy the timeline and arrange the blue boxes in appropriate places along the line. Atmosphere timeline Now 4,500 million 3,000 million 2,000 million 1,000 million 500 million 200 million H2O N2 O2 No gases CO2 NH3 CH4 H2 and He Volcanoes Algae Plants

7. All positions are approximate Timeline answers No gases Plants Algae Volcanoes Now 4,500 million 3,000 million 2,000 million 1,000 million 500 million 200 million O2 N2 H2O CO2 NH3 CH4 H2 and He

8. Use the graph to estimate the answers. How long ago was the atmosphere 75% CO2? How long ago were the CO2 and N2 levels in the atmosphere equal? How long ago was the atmosphere 50% nitrogen? 100% carbon dioxide nitrogen 50% Composition percentage oxygen now 0% 0 5,000 3,000 Time (millions of years) Changing gas levels Approx 4,000M Approx 3,300M Approx 2,000M

9. Contents Earth and Atmosphere Development of the atmosphere O3 and CO2 The Earth’s structure Plate tectonics Rocks Summary activities

10. 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. Earth Ozone: a vital filter 3O2 2O3 oxygen ozone Harmful UV rays stopped with ozone layer Harmful UV rays reach Earth’s surface without ozone layer

11. The carbon cycle

12. CO2 release or consumption?

13. Over millions of years the carbon cycle has maintained a constant, low percentage (approx. 0.03%) of carbon dioxide in the atmosphere. In 1860, the CO2 level was about 289 ppm (parts per million). Here is a table showing the CO2 levels over a recent 10-year period. Carbon dioxide and temperature • What percentage change is this and does it matter?

14. From air trapped in Antarctic ice, we have a good idea of CO2 concentrations going back 160,000 years. 200ppm CO2 300ppm CO2 Changing CO2 concentrations We also know the temperatures over the same period. The very warm interglacial period of 130,000 years ago was accompanied by CO2 levels of around 300 ppm. The previous great Ice Age had CO2 levels around 200 ppm. Which label goes with each picture?

15. Normally the Earth absorbs heat and emits heat at the same rate. Because of this the temperature remains constant. Certain gases, like CO2 and methane, act like a greenhouse. They let heat in but do not let it out. This is called the greenhouse effect. This means that the more CO2 there is, the hotter planet Earth is! Earth More CO2 balanced same temp Earth The greenhouse effect Heat loss Heat from sun Heat loss Heat from sun hotter And hotter! And hotter

16. Contents Earth and Atmosphere Development of the atmosphere O3 and CO2 The Earth’s structure Plate tectonics Rocks Summary activities

17. The Earth’s structure Beneath the atmosphere the Earth consists of 3 main layers:

18. The temperature is high and the outer core is molten. Towards the centre, high pressure makes the inner core solid. Intense heat is generated in the inner core by the decay of radioactive elements like uranium. 1,300 km 1,110 km 3,000 km The core The core extends to about half the radius of the Earth. It is made mostly from iron and nickel and is where the Earth’s magnetic field comes from. It is very dense. 5,500 C Inner core Outer core

19. The mantle extends outwards from the core to the crust: a distance of about 2,900 km. It is mostly a semi-molten liquid upon which the Earth’s crust floats. The heat coming from the core generates convection currents in the viscous mantle that cause the crust above to move. 2,900km The mantle Mantle

20. The crust is the thin layer of rock at the surface upon which we live. Eight elements make up over 98% of the Earth’s Crust – although they are virtually entirely in the form of compounds. % 20-60 km The crust Crust

21. I’m a viscous semi-solid withconvection currents circulating in me. I’m iron and nickel too, but I’m liquid. I just hang around on the outside. I’m really very thin and am mostlysilicon, oxygen and aluminium. I am dense, very hot, made mostly ofsolid iron and nickel. What am I? Mantle Outer core Atmosphere Crust Inner core

22. Sections of the Earth Atmosphere Outer core Crust Mantle Inner core

23. Contents Earth and Atmosphere Development of the atmosphere O3 and CO2 The Earth’s structure Plate tectonics Rocks Summary activities

24. The crust is made of about twelve plates. These are like big rafts floating on the semi-molten mantle. Convection currents within the mantle cause the plates to move. Although they only move about 2 cm a year this can have huge effects over long periods of time. Tectonic plates

25. Why do plates move?

26. When two oceanic plates move apart molten rock rises to the surface. sea floor spreading oceanic plate magma rising Sea floor spreading

27. On average, the plates only drift about 2cm/year. However, 2cm multiplied by a million is a long way! Scientists think the continents were originally all together in asuper-continent called Pangaea. Over millions of years they have drifted to their present positions on the floating tectonic plates. Pangaea Millions of years Continental drift

28. Continental drift

29. The theory is supported by several pieces of evidence. For example, if we consider Africa and South America there is: The “jigsaw fit”. The similarities in the rock layers from Africa and South America. Similarities in the type and age of fossils. Evidence of related species that definitely did not swim the Atlantic Ocean! Jigsaw fit Similar rocks and fossils Evidence for continental drift

30. Plate boundaries

31. volcano oceanic plate magma rising continental plate Effects at plate boundaries When a continental plate and an oceanic plate meet, the effects include: • plates juddering past each other producing earthquakes • the continental plate buckles upwards while the oceanic plate subducts (goes underground) • volcanoes result from the rising magma (melted oceanic plate)

32. Contents Earth and Atmosphere Development of the atmosphere O3 and CO2 The Earth’s structure Plate tectonics Rocks Summary activities

33. There are three main types of rocks: Igneous – formed when molten rock cools. Sedimentary – formed by the “cementing together” of small grains of sediment. Metamorphic – rocks changed by the effect of heat and pressure. All of these are involved in a continuous flow of rock from the surface underground only to emerge again later as part of the on-going rock cycle. Types of rocks

34. These are rocks formed by the cooling of molten rock (magma). volcano magma Igneous rocks Magma cools and solidifies forming igneous rocks.

35. Igneous rocks divide into two main groups: Intrusive igneous Extrusive igneous • Intrusive igneous rocks, like granite, are formed when magma solidifies within the ground. • Extrusive igneous rocks, like basalt, are formed when magma solidifies above the ground. Types of igneous rocks

36. The more slowly a rock changes from liquid to solid the bigger the crystals grow. • Intrusive igneous rocks that cool really slowly can have very big crystals. Extrusive igneous rocks that cool really quickly can have a glassy appearance. Igneous rocks and crystal size Intrusive igneous rocks, like granite, usually have clearly visible crystals. Extrusive igneous rocks, like basalt, have crystals that are usually small.

37. Surface rocks seem to be gradually reduced in size by weathering processes. Chemical weathering occurs when chemicals, such as those in acid rain, ‘eat’ away certain rocks. Physical weathering relates to rocks being broken down by the action of wind, rain and sun. For example, during the freezing and thawing of water in the cracks of rocks, the expansion of water makes the rocks splinter. The small broken fragments wash into rivers and, eventually, reach the sea where they settle as sediment. Chemical and physical weathering

38. Sedimentary rocks are rocks formed when particles of sediment build up and are “cemented together” by the effect of pressure and minerals. Rocks are broken up by the action of weather sea Sedimentary rocks Sedimentary rocks Fragments washed to the sea

39. Sedimentary rocks tend to have visible grains of sediment. Sometimes they contain fossils. They are usually softer than igneous rocks. Examples of sedimentary rocks are sandstone and mudstone. Getting older Types of sedimentary rocks Sandstone is formed from the cementing together of grains of sand.

40. Metamorphic rocks are formed by the effect of heat and pressure on existing rocks. This can greatly affect the hardness, texture and layer patterns of the rocks. Pressure from surface rocks metamorphic rock forming here magma heat Metamorphic rocks

41. Marble, slate and schist are metamorphic. Limestone is a rock often formed from the sediment of shells. Temperature and pressure cause the rock to reform as small crystals that are much harder. This is marble. It is used as a hard and decorative stone in buildings, sculptures etc. Slate is formed when pressure squeezes mudstone into plate-like grey sheets. It is used in roofing. Schist and mica are formed when mudstone is subjected to very high temperatures and pressure. Again, they contain layers, which is typical of many (but not all) metamorphic rocks. Types of metamorphic rocks

42. Match the rock with the correct description. Give an example of this type of rock. What’s the rock?

43. The rock cycle

44. Contents Earth and Atmosphere Development of the atmosphere O3 and CO2 The Earth’s structure Plate tectonics Rocks Summary activities

45. Glossary (1) • atmosphere – The gases that surround the Earth. • core – The central part of the Earth, divided into a solid inner section and molten outer section. • crust –The outer section of the Earth, made up of plates. • igneous – A rock formed by the crystallization of magma. • mantle – The layer of molten, semi-solid rock under the Earth’s crust. • metamorphic – A rock formed when an existing rock is changed by heat or pressure.

46. Glossary (2) • ozone – A gas made up of three oxygen atoms, which forms a layer that filters harmful UV rays from the sun. • plate – A large section of rock that floats on the Earth’s mantle and forms part of the crust. • plate tectonics – A theory that movement of the Earth’s plates over time is responsible for the current position of continents, and the creation of mountains and volcanoes. • sedimentary – A rock made up of layers of sediment.

47. Anagrams

48. Multiple-choice quiz