P1,P2,P3 OCR 21 ST CENTURY SCIENCE

1. P1,P2,P3OCR 21ST CENTURY SCIENCE Revision from BBC Bitesize I want to…. Jump to P1 Jump to P2 Jump to P3 Start from beginning Created by green500 TES

2. P1 • THE EARTH IN THE UNIVERSE • INCLUDING: • Earth, stars, galaxies and space • How the Earth is changing • Seismic waves

3. Earth, stars, galaxies and space • Earth, stars, galaxies and space • The Earth is one of the eight planets orbiting the Sun, and there are many other members of the Solar System including asteroids, moons and planets. Data provides the answers to many questions on this subject, but some questions remain unanswered. • The Earth and the Universe • The Universe is considered to be everything there is, though most of it is thought to be empty. • Much is now known about the Earth and the place of the Earth in the Universe, for example: • the diameter of the Earth is 12,800km (7,953 miles) • the diameter of the Sun is 109 times that of the Earth’s • the Earth is 150 million km (93 million miles) from the Sun • the distance to the nearest star is four light years.

4. Earth, stars, galaxies and space • The Solar System • The Earth is just one of the eight planets orbiting the Sun, which is a star. The orbits all lie in the same plane, and the planets all go round in the same direction. • There are many other members of our Solar System: • asteroids are much smaller than planets, and orbit the Sun. Most of the asteroids are between the planets Mars and Jupiter, but some come close to the Earth • moons orbit planets. Most are tiny. Only a few are as large as our Moon, which is nearly a sixth of the diameter of the Earth • comets have different orbits to those of planets, spending much of their orbital time far from the Sun. Comets are similar in size to asteroids, but are made of dust and ice. The ice melts when the comet approaches the Sun, and forms the comet’s tail.

5. The Sun • The Sun • Nearly all of the mass in our Solar System is in the Sun. The Sun is very large. Its diameter is 109 times the Earth's. The Sun is the source of nearly all the energy we receive. For many years, it was a mystery as to where this came from and this baffled the leading scientists. It is now understood that the nuclear fusion is the energy source. In nuclear fusion, smaller nuclei come together and form larger nuclei. For example hydrogen nuclei are joined together to make helium nuclei. This releases enormous amounts of energy. • hydrogen nucleus + hydrogen nucleus   →   helium nuclei • In stars larger than our Sun helium nuclei can be fused together to create larger atomic nuclei. As the Earth contains many of these larger atoms, like carbon, oxygen, iron, etc, scientists believe that our Solar System was made from the remains of an earlier star.

6. Stars form from massive clouds of dust and gas in space Gravity pulls the dust and gas together

7. How stars and planets are formed • How stars and planets are formed • As the gas falls together, it gets hot. A star forms when it is hot enough for anuclear fusion reaction to start. This releases energy, and keeps the star hot. The outward pressure from the expanding hot gases is balanced by the force of the star's gravity. This happened about 5 billion years ago. This is quite recent in the history of the Universe, which is currently believed to be 14 billion years old. • Gravity pulls smaller amounts of dust and gas together, which form planets in orbit around the star.

8. Looking at the sky • Looking at the sky • The radiation that distant stars and galaxies produce gives us information about the distances to stars, and about how they are changing. In the future, this may allow us to find out if life exists on planets around some of these stars. • Everything we know about stars and galaxies has come from the light, and other radiations, that they give out. This has become more difficult to see from the Earth’s surface, as light pollution from towns and cities interferes with observations of the night sky. • Looking at the sky with the naked eye shows the Sun, Moon, stars, planets and a few cloudy patches called nebulae. When telescopes were invented and developed, astronomers could see that some of the nebulae were in fact groups of millions of stars. These are galaxies. • Parallax • Powerful telescopes allowed astronomers to answer a question that had baffled scientists since the astronomer Copernicus (1473-1543) first suggested that the Earth moved around the Sun. If the Earth moves, you would expect to see a different view of the stars at different times of the year, in the same way as the room you are in looks slightly different if you move your head to one side. That is to say everything seems to move in the opposite direction to your head, but the objects close to you seem to move more. This effect is called parallax. So if the Earth was moving, why did the stars always look the same? • The answer to the question was revealed by more powerful telescopes. These showed that nearby stars do seem to move from side to side and back every year when compared with very distant stars, but that the amount of movement is tiny.

9. Finding the distance of a star using parallax The second nearest star to us is Proxima Centauri. The Sun is the nearest. It seems to move through an angle of 1.5 seconds between January and June. As one second = 1/60 of a minute, and one minute = 1/60 of a degree, this tiny movement, which is less than a thousandth of the diameter of the Moon, needed powerful telescopes and accurate measurement to observe.

10. Light Pollution & telescopes • In the last 200 years, it has become very difficult to make astronomical observations in industrialised countries such as the UK. This is not just because of cloudy weather or air pollution. It is due to the bright lights found in cities and towns, and on roads. This light pollution means that it is hard for many people to see more than a few of the very brightest stars at night. • Telescopes • Telescopes are now placed in the few remote, dark places left on our planet, or out in orbit around the Earth. • The Very Large Telescope is part of the Paranal Observatory that is built on top of the Cerro Paranalmountain, which is 2,635 m high, in the Atacama Desert in Chile.

11. More On Telescopes • Telescopes in space, such as the Hubble Space Telescope, can observe the whole sky. They are above light pollution and above dust and clouds in the atmosphere. However, they are difficult and expensive to launch and maintain. If anything goes wrong, only astronauts can fix them.

12. Beyond Our Solar System • Beyond our Solar System • The Sun is 150 million km(93 million miles) from the Earth, but that’s a tiny distance compared with the distance to other stars, or other galaxies. Larger units of distance are used for these measurements. One popular measurement is the light-year. • Light-years • A light-year is the distance light travels in a year. Light travels very fast (300,000 km/186,282 miles per second), and takes only about eight minutes to reach us from the Sun. It takes over four years to reach us from the next nearest star (Proxima Centauri), and 100,000 years to cross the Milky Way galaxy. We say that the distance to the next nearest star is four lightyears, and the diameter of the Milky Way is 100,000 light years. • The most distant galaxies observed are about 13,000 million light-years away. However, measuring distances to other stars, and to very distant galaxies, is not easy, so the data is uncertain.

13. Measurement uncertainties • Measurement uncertainties • When initial distances to stars were being established more than one method was employed. After establishing distances of nearby stars using the parallax method, the 'brightness method' was used to approximate distances to further stars. Other methods were also used. • Each method had its own assumptions. For example, with the parallax method an assumption made is that during the total time in which the measurement is taking place, distance remains constant between the two stars. • As methods were reliant on each other, a certain level of uncertainty is found in the results. A cluster of young stars in the Small Magellanc Cloud dwarf galaxy

14. Ideas about Science • Ideas about science - developing explanations • Different explanations can be developed to illustrate the theory that the dinosaurs were destroyed by an asteroid impact. • Data and explanations • Data statements tell you facts, and may contain measurements. For example, look at these three statements: • asteroids are small objects orbiting the Sun • some asteroids have orbits close to the Earth • the dinosaurs died out at about the same time as a large crater was made in Mexico. • Explanations seek to explain the data, and formulating an explanation requires imagination and creativity. One explanation is that an asteroid collision may have killed off the dinosaurs. The asteroid impact would have created dust that blocked out light and heat from the Sun.

15. Predictions • Predictions • A good explanation will explain data, and link together things thatwere not thought to be related. It should also make predictions. • asteroids often contain the rare metal iridium - data • a huge asteroid impact would send iridium dust throughout the world - prediction • sedimentary rocks from the time the dinosaurs died out contain iridium - data • when the asteroid crashed, the iridium came from the dust tha tblocked out the Sun - explanation. • Data and predictions can be used to test an explanation, but you have to be careful. When an observation agrees with the prediction, it makes you more confident in the explanation, but it does not prove that the explanation is true. • The opposite is also correct. When an observation disagrees with a prediction, it makes you less confident in the explanation, but it does not prove that the explanation is wrong. The data may be faulty. • The asteroid theory is not the only one about the death of the dinosaurs. Other are: • there were huge volcanic eruptions in India at the time the dinosaurs died out - data • big volcanic eruptions cause dust clouds thatblock out the Sun - data • the big Indian eruptions could have killed out the dinosaurs by cooling the Earth - explanation. • Unanswered questions • Not all scientific questions have answers at this time. For some of the questions there is not enough data yet. An example of this is the question: is there life on distant planets? For other questions, there may never be the data you need. An example of this is: what happened before the ‘Big Bang’ when the Universe was created?

16. Galaxies • Galaxies • Galaxies contain thousands of millions of stars. For many years, it was thought that our galaxy, which is the Milky Way, was the only one that existed, and that the blurry nebulae that could be seen were clouds of dust and gas in the Milky Way. • Observations of many of these nebulae by astronomers such as Edwin Hubble showed they were in fact galaxies outside the Milky Way, and that distant galaxies are all moving away from us. • The beginning and end of the Universe • Hubble’s observations led to the ‘Big Bang’ explanation of the beginning of theUniverse, and set a date for this at 14,000 million years ago. • There are many questions left unanswered about the beginning and end of the Universe. Observations suggest it contains a lot of ‘dark matter’ that cannot be seen, and this is not yet clearly understood. • Perhaps the Universe will continue to expand in the way it is at the moment. Perhaps gravity will eventually win and pull all the fleeing galaxies back together again. Better observations of very distant galaxies and a better understanding of the mysterious ‘dark matter’ are needed before these will be understood. • Hubble’s Law- Higher tier • The astronomer Edwin Hubble (1889-1953) measured the distance to many galaxies, and also the speeds with which they are moving away from us. He found a strong correlation between these factors.

17. Some galaxies do not fit exactly on the line of correlation This correlation is summed up in Hubble’s Law which says that the speed at which a galaxy moves away from us is proportional to its distance from us. The causal link which explains this law is that space itself is expanding. As the Universe expands, galaxies that are already further apart will increase in separation even more, and so move away at higher speeds.

18. Age of the Universe • Age of the Universe • The development of powerful telescopes allowed astronomers to see distant galaxies. The light observed was shifted towards the red end of the spectrum. This phenomenon is known as red-shift. The degree to which light has been shifted indicates how fast the galaxies are moving away. • In general, the further away the galaxy is, the faster it is moving away from the Earth. The motions of the galaxies themselves suggest that space itself is expanding. • It is estimated that the Universe is approximately 13.7 billion years old. Evidence suggests that our Solar System formed around 4.5 billion years ago, so it is around one-third the age of the Universe. • The eventual fate of the Universe is hard to predict due to the uncertainty in measuring such large distances and studying motion of distant objects. A better idea of the mass of the Universe would lead to better predictions.

19. How the Earth is changing • The theory of plate tectonics is now well established. Continental drift is happening as tectonic plates move, with earthquakes and volcanoes often occurring around their edges. • Evidence from rocks • Rocks provide evidence for changes in the Earth. In 1785 James Hutton presented his idea of a rock cycle to the Royal Society. He detailed ideas oferosion and sedimentation taking place over long periods of time, making massive changes to the Earth’s surface. • Geologists can use other evidence from the rocks themselves such as: • looking at cross-cutting features (rock that cuts across another is younger) • using fossils (species existed/ became extinct during certain time periods) • deepness of the rock (younger rocks are usually on top of older ones). • This kind of evidence only shows that some rocks are older than others. To get a more accurate idea of the age of rocks radioactive dating is used.

20. Wegener’s theory • Wegener’s theory • Alfred Wegener (1880 - 1930) • Alfred Wegener proposed the theory of continental drift at the beginning of the 20th century. His idea was that the Earth's continents were once joined together, but gradually moved apart over millions of years. It offered an explanation of the existence of similar fossils and rocks on continents that are far apart from each other. But it took a long time for the idea to become accepted by other scientists.

21. Before Wegener • Before 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 Earth's crust. If the idea was correct, however, mountains would be spread evenly over the Earth's surface. We know this is not the case. The heating effect of radioactive materials inside the Earth prevents it from cooling. • Wegener suggested that mountains were formed when the edge of a drifting continent collided with another, causing it to crumple and fold. For example, the Himalayas were formed when India came into contact with Asia. • This slideshow explains Wegener's theory.

22. Earth around 200 million years ago, at the time of Pangaea The single landmass began to crack and divide, due to the slow currents of magna beneath it The positions of the continents today

23. Wegener’s evidence • Wegener’s evidence for continental drift was that: • the same types of fossilised animals and plants are found in South America and Africa • the shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle • matching rock formations and mountain chains are found in South America and Africa.

24. Ideas about science - the scientific community • Publishing and peer review • Scientists report their ideas to the scientific community. They present them at conferences and then write them up in journals or books. • At conferences, other scientists will listen and debate the new ideas. Before journals or books are published, other expert scientists read the new ideas and decide if they are sensible. This is called peer review. • Wegener presented his ideas at a conference in 1912, and then published them in a book in 1915. • Repeating experiments • Scientists do not usually accept the results of experiments until someone else has repeated them to get the same results. It is hard to set up experiments in geology and astronomy, so new theories need support from different observations.

25. MORE • Different explanations • Data often allows more than one possible explanation, so different scientists can have different explanations for the same observations. • Wegener’s ideas could certainly explain similar fossils turning up in different continents, but other geologists thought that there were once ‘land bridges’ between continents, allowing animals to travel between them. • The different backgrounds of different scientists can affect their judgements, so they may have quite different explanations for the same data. • Wegener was trained as an astronomer and a meteorologist. Many geologists did not think that he had the right background to judge geological theories. • Wagener's new explanation becomes accepted • The old geological theory explained mountains as wrinkles made by the Earth shrinking as it cools down. • There was no clear explanation of how continents could move about - a new scientific explanation often needs new supporting evidence to convince scientists that it is correct. • Then, in the 1950s, evidence from magnetism in the ocean floor showed that the seafloors were spreading by a few centimetres each year. This showed movement of large parts of the Earth’s crust, now called tectonic plates. This new evidence allowed Wagener's theory to be accepted. • A scientific explanation is rarely abandoned just because some data does not correspond to it, but it is safer to stick with a theory that has worked well in the past.

26. Seafloor spreading • Seafloor spreading • In the centres of many oceans, there are mid-ocean ridges. At these places, thetectonic plates are moving apart. Molten material, known as magma from inside the Earth oozes out and solidifies. This movement of the mantle is referred to as convection due to heating by the core of the Earth. This process is calledseafloor spreading. It results in seafloors spreading by a few centimetres each year.

28. Inside the Earth • Inside the Earth • All our evidence for changes in the Earth comes from looking at rocks. Folds and fossils in sedimentary rocks, radioactive dating and the weathering of ancient craters show that the oldest rocks are about 4000 million years old. That means the Earth must be at least as old as this. • The only thing that we have been able to observe directly is the Earth’s crust, which is the very thin outer rocky layer. • Evidence from earthquakes shows that the Earth has a very dense core surrounded by a solid mantle.

29. Cross section showing structure of the Earth The Earth is almost a sphere. These are its main layers, starting with the outermost: The crust, which is relatively thin and rocky The mantle, shown here as dark red, which has the properties of a solid, but can flow very slowly The outer core, shown as orange, which is made from liquid nickel and iron The inner core, shown as yellow, which is made from solid nickel and iron

30. The Earth's magnetic field - Higher tier • The Earth's magnetic field - Higher tier • The typical speed of seafloor spreading is slow: about 10 cm per year. When themagma oozing out of mid-ocean ridges solidifies into rock, the rock records the direction of the Earth’s magnetic field. The Earth’s magnetic field changes with time, and sometimes even reverses its direction. These changes are recorded in the rocks. The same magnetic patterns are seen on both sides of the mid-ocean ridges.

32. Plate tectonics - Higher tier • Plate tectonics - Higher tier • The Earth’s crust, together with the upper region of the mantle, consists of huge slabs of rock called tectonic plates. These fit together rather like the segments on the shell of a tortoise. Although the mantle below the tectonic plates is solid, it does move. This movement is very, very slow – a few centimetres every year. This means that the continents have changed their positions over millions of years.

33. Movement of tectonic plates - Higher tier • Movement of tectonic plates - Higher tier • Volcanoes, mountains and earthquakes occur at the edges of tectonic plates - their creation depends on the direction the plates are moving. • Volcanoes • If the plates are moving apart, as at mid-ocean ridges, volcanoes are produced as molten magma is allowed to escape. This happens in Iceland. • Mountains • If the plates are moving towards each other, the edges of the plates crumple, and one plate ‘dives’ under the other. This is called subduction. It produces mountains, like the Himalayas. The friction of the movement can also melt rocks and produce volcanoes. • This is also part of the rock cycle, because the plate that dives under the other one becomes part of the mantle and emerges much later from volcanoes and in seafloor spreading.

35. MORE • There are two other ways in which mountains can be formed. At destructive margins mountain chains can be formed as plates push against each other. If an ocean closes completely then continents can collide. This occurs slowly but the collision would still result in the formation of a mountain chain. • Earthquakes • If the plates are moving sideways, stresses build up at the plate boundary. When the stress reaches some critical value, the plates slip suddenly, causing an earthquake. It is hard to predict when such an event may happen.

37. Detecting wave motions • Detecting wave motions • A seismometer detects the vibrations of an earthquake. • The vibrations of an earthquake are detected using a seismometer that records the results in the form of a seismogram. • The vibrations that are detected from the site of an earthquake are known as seismic waves.

38. Seismic waves • Vibrations from an earthquake are categorised as P or S waves. They travel through the Earth in different ways and at different speeds. They can be detected and analysed. • P and S waves • A wave is a vibration that transfers energy from one place to another without transferring matter (solid, liquid or gas). Light and sound both travel in this way. • Energy released during an earthquake travels in the form of waves around the Earth. Two types of seismic wave exist, P- and S-waves. They are different in the way that they travel through the Earth. • P-waves (P stands for primary) arrive at the detector first. They are longitudinal waves which mean the vibrations are along the same direction as the direction of travel. Other examples of longitudinal waves include sound waves and waves in a stretched spring.

40. Amplitude, wavelength and frequency • Amplitude, wavelength and frequency • You should understand what is meant by the amplitude, wavelength and frequency of a wave. • Amplitude • As waves travel, they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position. Take care: the amplitude is not the distance between the top and bottom of a wave. It is the distance from the middle to the top.

41. Wavelength and Frequency • Wavelength • The wavelength of a wave is the distance between a point on one wave and the same point on the next wave. It is often easiest to measure this from the crest of one wave to the crest of the next wave, but it doesn't matter where as long as it is the same point in each wave. • Frequency • The frequency of a wave is the number of waves produced by a source each second. It is also the number of waves that pass a certain point each second. The unit of frequency is the hertz (Hz). It is common for kilohertz (kHz), megahertz (MHz) and gigahertz (GHz) to be used when waves have very high frequencies. For example, most people cannot hear a high-pitched sound above 20kHz, radio stations broadcast radio waves with frequencies of about 100MHz, while most wireless computer networks operate at 2.4GHz.

42. Wave Speed • Wave speed • Wave speed is the velocity at which each wave crest moves and is measured in metres per second (m/s). The wave speed only depends on the material the wave is travelling through. The distance travelled by a wave is calculated using this equation: • Distance = speed x time • The speed of a wave - its wave speed (metres per second, m/s)- is related to its frequency (hertz, Hz) and wavelength (metre, m), according to this equation: • wave speed = frequency x wavelength • For example, a wave with a frequency of 100Hz and a wavelength of 2m travels at 100 x 2 = 200m/s. • The speed of a wave does not usually depend on its frequency or its amplitude.

43. Radiation Life – P2INCLUDING: • Electromagnetic radiationBenefits and risks Global warmingWaves and communication

44. Light is one of the family of radiations called the electromagnetic spectrum. Some types of electromagnetic radiation are used to transmit information such as computer data, telephone calls and TV signals. • The electromagnetic spectrum • Refraction from a prism • The pattern produced when white light shines through a prism is called the visible spectrum. • The prism separates the mixture of colours in white light into the different colours red, orange, yellow, green, indigo and violet. • In fact, visible light is only part of the electromagnetic spectrum. It’s the part we can see.

46. Photons and ionisation • Photons and ionisation • Electromagnetic radiation comes in tiny ‘packets’ called photons. • The photons deliver different quantities of energy, with radio photons delivering the smallest amount, and gamma photons delivering the greatest amount of energy. • A higher frequency of electromagnetic radiation means more energy is transferred by each photon. • If the photons have enough energy, they can break molecules into bits called ions. This is called ionisation. These types of radiation are called ionising radiation. This radiation can remove electrons from atoms in its path. • In the electromagnetic spectrum only the three types of radiation, which have the photons with most energy, are ionising. These are ultraviolet, X-rays andgamma rays. • Damaging to health - Higher tier • The ions produced when ionising radiation breaks up molecules can take part in other chemical reactions. If these chemical reactions are in cells of your body, the cells can die or become cancerous. This is the reason that ionising radiation can be damaging to health.

47. Energy and intensity • Energy and intensity • The intensity of electromagnetic radiation is the energy arriving at a square metre of surface each second. This depends on two things: the energy in each photon, and the number of photons arriving each second. • To have the same intensity, a beam of red light would need ten times as many photons as a beam of ultraviolet, and a beam of microwaves would need a million times as many. • Energy of 1 ultraviolet photon   =   Energy of 10 red photons   =   Energy of 1,000,000 microwave photons • Absorption of radiation - Higher tier • All forms of electromagnetic radiation deliver energy. This will heat the material that absorbs the radiation. The amount of heating depends on the intensity of the radiation, and also the length of time the radiation is absorbed for.

48. Electromagnetic radiation • An object which gives out electromagnetic radiation is called a source of radiation. • Something which is affected by the radiation is a detector. • Lower intensity of radiation • Further from the source, the detector receives a lower intensity of radiation. As the photons spread out from the source, they are more thinly spread out when they reach the detector. The intensity may also decrease with distance due to partial absorption by the medium it travels through.

49. Ionising radiation • Ionising radiation • Ionising radiation can break molecules into smaller fragments. These charged particles are called ions. As a result, ionising radiation damages substances and materials, including those in the cells of living things. The ions themselves can take part in chemical reactions, spreading the damage. • Ionising radiation includes: • ultraviolet radiation, which is found in sunlight • x-rays, which are used in medical imaging machines • gamma rays, which are produced by some radioactive materials.

50. MORE • Non-ionising radiation • Not all types of electromagnetic radiation are ionising. Radio waves, light and microwaves are among them. • Microwaves • Microwaves are used to heat materials such as food. The molecules in the material absorb the energy delivered by the microwaves. This makes them vibrate faster, so the material heats up. • The heating effect increases if: • the intensity of the microwave beam is increased • the microwave beam is directed onto the material for longer. • So you need to cook food for longer in a less powerful microwave oven. This is why they have power ratings, and food labels recommend different cooking times depending on this.