KS4 Changes to the Earth and atmosphere

1. KS4 Changes to the Earth and atmosphere

2. The Atmosphere

3. The Earth was formed about 4500 million years ago. The very first atmosphere mainly consisted of hydrogen and helium gases. Frozen giant planets like Saturn and Jupiter still have atmospheres like this but on the warmer, smaller Earth these light gases were largely lost into space. Jupiter Saturn In the beginning -

4. During the first billion years on Earth there was intense volcanic activity. This produced the next early atmosphere. It would have contained large quantities of carbon dioxide (CO2), along with methane (CH4) , and ammonia (NH3). This is rather like the atmosphere on Mars and Venus today. The Earth’s atmosphere would also have contained water vapour which condensed to form the oceans. Mars Venus The early atmosphere

5. Carbon dioxide reacted with rocks and much became trapped in them. The evolution of algae some 3000 million years ago, and subsequently plants which successfully colonised 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

6. 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. Nitrogen makes an appearance

7. 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

8. Activity Copy the timeline and arrange the blue boxes in appropriate places along the line. Now 4500 million 3000 million 2000 million 1000 million 500 million 200 million H2O N2 O2 No gases CO2 NH3 CH4 H2 and He Volcanoes Algae Plants

9. All positions are approximate Answer No gases Plants Algae Volcanoes Now 4500 million 3000 million 2000 million 1000 million 500 million 200 million O2 N2 H2O CO2 NH3 CH4 H2 and He

10. What was the main gas in the atmosphere around 3500M years ago? Where did this gas come from? What process led to reduction in CO2 levels? What gas protects life from harmful UV radiation? What % of the present atmosphere is oxygen? Activity Carbon dioxide Volcanoes Photosynthesis Ozone 21%

11. 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? Activity 100% carbon dioxide nitrogen 50% Composition percentage oxygen now 0% 5000 3000 0 Time (millions of years) Approx 4,000M Approx 3,300M Approx 2,000M

12. Find the words in the word-search Write a sentence about how each has played a part in the evolution of the Earth’s atmosphere. Activity Ammonia Carbon dioxide Helium Hydrogen Methane Nitrogen Oxygen Ozone Photosynthesis Volcano

15. 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?

16. From air trapped in Antarctic ice, we have a good idea of CO2 concentrations going back 160,000 years. 200ppm CO2 300ppm CO2 Greenhouse effect 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?

17. 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 means: the more CO2 there is, the hotter planet Earth is! Earth More CO2 balanced same temp Earth Greenhouse effect Heat loss Heat from sun Heat loss Heat from sun hotter And hotter! And hotter

18. The Earth’s Structure

19. The Earth’s Structure Beneath the atmosphere the Earth consists of 3 main layers:

20. 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 decay of radioactive elements like uranium. 1300 km 1110 km 3000 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. 5500 C Inner core Outer core

21. 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. 2900km The mantle Mantle

22. 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

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

24. Attach labels to the correct part of the diagram. Atmosphere Outer core Crust Mantle Inner core

25. Plate Tectonics

26. 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/year this can have huge effects over long periods of time. Tectonic plates

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

29. 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 a super-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

30. Continental Drift

31. The theory is supported by several pieces of evidence. For example, if we consider Africa and South America there is: The “jig-saw 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! Jig Saw fit Similar rocks and fossils Evidence for Continental Drift

32. Plate boundaries

33. volcanoes result from the rising magma (melted oceanic plate) 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 whilst the oceanic plate subducts (goes underground)

34. Find the words and write a sentence about how each one has something to do with plate tectonics. Drift Earthquake Fossil Jigsaw Magma Pangaea Plates Subduct Volcano Activity