gr7 - Moon and Earth relationships - NS.pdf

Uni t 1 Sol ar ene rgy and the Earth What you alread y know .-When ttie no In Grade 4 you learnt · fro,6m the Su_n, lt. but summer in that the Sun is made [ spring, of hot gas and gives ond south get : ~ get equal sun. out heat and light. _:;. v The Sun provides hegt :,) $' 1' and light to the Earth...

Uni t 1 Sol ar ene rgy and the Earth What you alread y know .-When ttie no In Grade 4 you learnt · fro,6m the Su_n, lt. but summer in that the Sun is made [ spring, of hot gas and gives ond south get : ~ get equal sun. out heat and light. _:;. v The Sun provides hegt :,) $' 1' and light to the Earth .J -;;- that living things can survive. You also Tearn t that the Earth moves around the Figure 15.1 Differing amoun ts of solar energy Sun in a pathw ay reach the Earth. called an orbit. nort✓ • ~ ~~a -~~~,, ~ In Grade 5 you discovered that the Earth takes about 365¼ days to travel once around the Sun, this is called a year. Other focus points of your studies were that the Earth spins on its own axis and the Earth takes approximately 24 hours to spin once - this is called a day. In Grade 6 you tearnt that during rotatio n the side of the Earth facing the Sun experiences daytim e and the oppos ite side of the Earth experiences night time. In the series of lessons that follow you will build on this knowledge and learn about how the tilt of the Earth and its rotatio n and revolution give rise to the seasons that are experienced on Earth and their relation to time. ,w A • ' Topic 15 The relation ship of the Sun to the Earth Planet Earth and Beyond 1. Describe the Earth's axis 2. How long does it take for the Earth to rotate once on its axis? 3. Name the star that lies at the centre of the solar system . . 4. How long does it take for the Earth to revolve around the Sun? Lesson 1 Solar energy and the Earth's seasons The Sun radiates heat and light in all directions. However, not all places on Earth receive the same amount of heat and light (solar energy). Let's explore the reasons why all places on Earth do not receive the same amount of solar energy. It is possible that the reasons for the seasons lie in space? SEPTEMBER Figure 15.2 The Sun radiates heat and light in all directions. Fa ct s which will help you underst d ho w se as on s an occur: . . nee in 24 hours. • The Earth rotates on its axis o m to be still, bu t it is • The Earth under your feet ma y see_ S . t pa s it or bit s th e un . spinning around hke a o n angle of 23,50 fro m • The Earth is tilted towards the Sun at a the vertical. Axis - N -- s Figure 15.3 The Earth is angled towards the Sun. • Figure 15.4 The Ea rth rot ate s on thi s ax is. The angle of the tilt is measured from th e Ea rth 's ax is at th e centre of th e Earth . W ha t is th e Earth's axis? The Earth's axis is an i!f,aginary line thr ough th e ce ntr e of th e Earth running from t he North Pole to th e So uth Pole. Th ink of the axis as as if it were a sti ck th at is pushed thr ou gh th e ex ac t middle of an orange from the stem to the navel of th e or an ge. I The changing seasons seasons: the divisions of the year into spring, summer, autumn and winter equator: an imagina ry line around the Earth Seasons occur because.the Earth is tilted slightly to one side. This affects the amoun t of light and heat that different parts of the Earth receive from the Sun on its yearly orbiL The angle of the tilt of the Earth is the same all the time. However, this means that places are either tilted toward s the Sun or away from it at different times of the year as the Earth revolves around the Sun. The result is that some places receive more light and heat at specific times of the year than they do at ·other. This pattern creates changing weathe r conditions as certain months of the year are hotter than others, and the length of day and night varies accordingly, giving us characteristic seasons during the year. Summer happens in th~ southern , hemisphere when the South Pole leans towards S\JJl Figure 15.5 The changin g seasons Places between the equator and the poles have four seasons: spring, summer, autumn and winter. At the equator, places are not as affecte d by the Earth's tilt because the Sun is always directly overhead. They tend to have a more consta nt climate . • Topic 15 The relationship of the Sun to the ~ At the poles, only the summer/winter diff erence is very clear. If the Earth were not tilted in space, there. would be no seasons anywhere on Earth - and day and night would always be exactly the same length. Cool fact: In places near the poles, such as north ern Norway, the Sun never sets for about six months of the yea r. It stays jus t above the horizon at night, which is why these places are known as the 'Lands of the Midnight Sun'. Basically there is daylight for half the year and dark for the other half of the year. 21 Mar ch Da~ s ore the som e leng th n both "ort n and sout h ~ern sohe re 21 Dec e~b er the Arcu c :s 1r con stan t darkness 21 Scp~_t::r····:--_,,~r crs;_:r.., r.,Jr)> :: ~qi_;c;:_or ErJ,.J_~- .._;, r;1 ~:, ·s ,.. ,..;t_ i_;1t8 rJ ".CJ:. r~;rJ~ C/ r~ ,','r]'j S 1_1;; S'."J neir .._~-1 c_;r rj from th';; ;'~ •r ~j, J ; • Figure 15.6 The orbiting Earth around the Sun creates seasons. As the Earth orbits the Sun, it spins on an axis tha t is tilted at approximately 23,5° in•-felation to the ver tical. It is always tilted the same angle, so in June the North Po le is turned towards the ~un and in December it is turned aw ay from the Sun. This means that in June the Northern He misphere has summer and it is winter in the south. Six months later the situation is reversed, so it is summer in the south and winter in the north. ,., • • Top ic 15 The relationship of the Sun to the Ear th hemisphere: half of the Earth, divided by the Equator When it is summer iri South Africa it is winter in Europe. · ' · Why? When it is summer in· Sou~h Africa, it is winter in Europe. In December, the southern point of the Earth's axis, the South Pole, leans towards the Sun. Places in the southern half of the world (Souther~ Hemisphere), such as South Africa, will then have summer. At the same time, places in the northern half, including Europe, have winter. This phenomenon is the result of the Earth's movements of rotation and revolution that are taking place combined with the Earth's tilt. @ hem winter and southe mmer happen when the misphere is tilted towards \ Sun Figure 15.7 When it is summer in South Africa, it is winter in Europe The closer you are to a heater the warmer you will be. The same principle applies to the Earth-Sun · system. The Sun's energy, heat and light, becomes heat that we can feel and light that can see when it is broken up by a solid object. This is heating by radiation, which you learnt about in Topic 11. The .Sun heats the Earth and the Earth heats the air around it. So the closer to the ground the warmer it will be. Also the stronger the source of heat, the warmer it will be - summer will be warmer as more solar energy is received. Differing amounts of solar energy lead to the seasons. This solar energy is called insolation, the amount of heat and light Earth receives from the Sun. in-sol-ation ~i~ incoming lnsolation: incoming solar radiation (heat and light) solar radiation . If the Southern Hemisphere receives more solar energy than the Northern Hemisphere it is summer in the Southern Hemisphere. When the Northern Hemisphere is tilted . towards the Sun, it receives more solar energy and it is summer there. ~ - . • Topic 15 The relationship of the Sun ·to the Earth . . summerin \ . ' north ern hemi sphe re (June) ~ . - ': .· .... ·.· ·.... su111mer in · :· . · .sout t,.e rn hemi sphe re . ;-(Qy cemb er) Figure 15.8 Seasons in the hem isphe res Word bank Solstices and equinoxes solstice: two dates, 22 December and 21 June, when the Sun reaches its high est point in the sky directly overhead one of the tropics, giving all places on Earth their long est or shor test day or nigh t of the year depending on ' whe ther they are in the northern or southern hemisphere There are three fact ors tha t create seasons: Distance from the equator is also a factor, the amo unt of insolation (solar radiation) the Earth receives, as well as the revolution of the Earth around the Sun and the tilt of the Earth on an axis of 23,5° as it rotates. T~e mid-winter and mid-summer positions of the Ear th in relation to the Sun are called the win ter and sum mer sols tice s. In the Southern Hemisphere, the sum mer .sols tice is on 22 December and the win ter sols tice is on 21 Jun e. The reverse is the case in the Northern Hemisphere. The sum mer solstice has the longest day and the win ter sols tice has the sho rtes t day in the yea~ ,- / 0 • Topic 15 . The relationship of the Sun to the Eart h The spring and autumn equinoxes are on 21 March and 22 September. Length of days are equal to length of nights. equinox: two I I j ' - dates, 21 March and 22 September, when the Sun's toys fall directly on the equator. All places on the earth experience equal night and day - 12 hours each 21 December 21 Ju·ne Summer solstice (in northern hemisphere) Winter solstice On northe Summer solstice (in soutti Wint~r solstice (in southern hemisphere) hemisphere) 0 0 Arctic circle 66½ N Arctic circle 66½ N North North Pole , , ~!;1fg"h~ 1~\ ~ ~- }"'~~ 1, Figure 15.q The summer and winter solstices At the equator, temperatures do not change much with the seasons. The further away from the equator, the greater the difference in summer and winter temperatures. The further away from the equator, the greater the differences in the length of day and night in winter and in summer. At the equato r there are approx imately twelve hours . sun's rays are spread of dayligh t and twelve hours of darkness out over a large .area every day. Heating the Earth - dispersed energy When the solar energy falls more directly on the Southern Hemisphere, the solar energy is spread over a s,:naller area and this concentration of energy results in it being summer, the hotter season, in the Southe rn Hemisphere. Figure 15.10 Disperse d solar energy 0 . . • Topic 15 The relationship of the Sun to the Earth .l( ~ Study Figure 15.11. At the equator and in the tropics (areas which lie as far as latitudes 23,5° north and south of the equator), the Sun's rays strike the Earth's surface almost directly. The Sun's energy is concentrated so these are the hotter places in the world and temperatures are higher. Near the polar areas, the $un's rays strike the surface at an angle and the energy is dispersed. The same amount of energy that is absorbed here in these temperate latitudes is spread over a far larger area in the polar regions. In fact, the area near the poles is roughly twice the area that is heated near the equator. Word bank latJtude: a measurement of how for away a place is from the equator dispersed: spread out or scattered The difference in the degree of solar heating at various latitudes is the main reason why air masses are set in motion, generating the world's weather systems. Warm air rises from the Earths' surface giving rise to low pressure areas, and cool air sinks towards the Earths' surface giving rise to high pressure areas. As the warm air rises the cool air moves in to take its place. This movement of air from areas of high pressure to low pressure generates wind. Wind contributes to the world's weather systems. It transfers heat and water vapour. ~ __ ..._______,;;,;. F~gu~e 15.11 Warm air rising creates areas of low pressure smkmg colder air creates areas of high pressure (HP). {LP) and ~e amount of solar energy detennines the amount of heat . th air, measured as temp t Th' in e . era ure. is affects air pressure th t . rise to moving air (wind) which t . · a gives . Th' con ains water vapour needed ~ rain. is weather varies from t ,or season o season. A • W1 Topic 15 The relationship of the S un to the Earth How the Sun's rays strike the Earth If you were to travel either northwards or southwards from the equator you would find that in general the weather would get colder. One reason for this drop in temperature is that the rays of the Sun strike the Earth at different angles in different places. The diagram given shows how the heating effect of the rays depends upon the angle at which they strike the ground. X and V are bundles of the Sun's rays with equal heating power when they reach the atmosphere. Think abou t it like this: bundle of rays Y Look at the diagrams alongside and work out: How many squares 1. would bundle X have to heat? How many squares 2. would bundle V have to heat? The Sun's rays strike Earth at different angles because the Earth's surface is curved. bundle of rays X Figure 15.12 Areas heated by midday Sun on 21 March · . \ • Topic 15 The relationship of the Sun to the Earth • S.ome ~ays are longer than others 21 March + 21 Septef!1ber 21 December The Sun on any particular day is highest in the sky at midday, and the higher the Sun is the greater its power to heat the Earth. s N The following three diagrams show how the height of the midday sun differs from one time of the year to another. As the height of the Sun in the sky changes, so the season changes too. On 22 December the Sun is almost directly overhead the southern tropic. The days are longer. On the 22 December the Sun does not set at the South Pole. In June the days are dark, the Sun is largely invisible. · Figure 15.13 Equatorial lands , .~~ une -• --- --- -- -- Figure 15.14 Southern Polar Region ~ 21 December 1 March · 2, September ~ Mid-latitude.regions are those 1 June areas where it is neither very hot nor very cold. In Figure 15.15 you will notice that on 21 December . the Sun is highest in the sky, it is summer and it is also the longest Figure 15.15 Southern mid-latitude regions day of the year. Look at how low the Sun travels ·in the sky in June in the winter. 21 June is the shortest day in the Southern Hemisphere. mid-latitude: mt e Tooic 15 The halfway betwp en the equator: and the Poles ri:1ln+;,.. _ _ In most parts of the world, summer and winter bring different temperatures, because the height of the midday sun differs from one time of the year to another. The length of the day also depends upon the season. 1. After studying the diagram alongsi~e, state whi~h .area shown on the diagram would be hottest, A or ~- III Individual Give a reason fo.r your ·ansvver,., I ' 2. \' Look at Figure 15.17. Dec1de which do the Sun is nearest to b~i,ng .ov South Africa. .. 1 I - .:. • • t• ' 21 March+ 21 September 21 J .......-........ 1<· t •. Decem ":, _ X, Y and Z are bundles of rays with equal heating power when they rea~h the atmosphere s .. N Figure 15.16 How the Sun's rays strike the Earth's surface Figure 15.17 Equatorial lands ; 3. 4. 5. 6. 7. Why do the Sun's rays strike Earth at different angles? Give two reasons. Why are the polar regions often called 'the Lands of the Midnight Sun'? What is the shortest day of the year in South Africa? During which season does South.Africa experience short days? In your own words explain t he meaning of the following t erms: a) equinox ~-.. b) solstice • Topic 15 The relationship of the Sun to the Earth I Lesson 2 Solar energy and life on Earth Without the Sun's energy there would be no life on Earth. How do plants use sunlight? photosynthesis: a process whereby plants use the Sun's energy, carbon dioxide from the air and water from the soil to produce energycontaining food Plants absorb light from the Sun as a source of energy to produce the food they need in order to live and grow. Plants use a process called photosynthesis in order to change sunlight into food. During photosynthesis water and carbon dioxide from the air are converted into sugars that nourish the plant. In Grade 8 you will study the process of photosynthesis more closely. Figure 15.21 Plants make food during photosynthesis. • Topic 15 The relations hip of the Sun to the Ea~ The energy flow into an ecosystem begins with the Sun. Almost all organisms get the energy they need directly or indirectly from the Sun. Primary producers or plants use the Sun's energy in the process of photosynthesis. These producers (plants) are eaten by animals or consumers. When this happens the Sun's energy, in the form of sugars, flows from producer to consumer. When plants and animals die, their remains are broken down by tiny organisms which live in the soil (decomposers). This produces nutrients which the plants absorb through their root systems. Energy flow through an ecosystem ecosystem: a network of interactions among and between organisms in their · environment decomposers: dead plants and animals ore decomposed by organisms called decomposers Energy that arrives as light from the Sun gives us almost all our energy, either directly by its warmth, or by providing the energy for plants to grow. decomposers Breakdown of organic matter soil, minerals ---- - matter absorbed by vegetation secondary consumers carnivores primary consumers herbivores Illfood Figure 15.26 Energy flow through on ecosystem • • ~pie 15 The relationship of the Sun to the Earth Lesson 3 Stored solar energy (fossil fuels) Plants can be converted into coal which is burnt as fuel. Coal, oil and natural gas are fossil fuels, meaning they were formed over millions of years from the remains of plants and small creatures. They store energy from the Sun that was absorbed by plants long ago. Let's explore the process of how coal was formed. Around 300 million years ago, the Earth's climate was very different from the climate now. Steamy tropical swamps grew undisturbed, with massive rain forest trees and strange~ giant ferns. This period lasted for millions of years; old trees died and fell into the swamp, and thick layers of dead wood built up and were covered by mud. The wood did not rot because it was protected from the air by the covering of mud. Sea levels rose and washed more mud and sand over the buried trees. As millions of years passed, the wood was compressed by the layers of mud and sand above, and it was altered to form coal. When we burn coal today, the energy we get is the Sun's energy from 300 million years ago, stored in the remains of the trees that grew then. The oldest coal was formed about 350 million years ago, and the process still continues in swamps. Peat is the earliest stage in the formation of coal. It has not yet been subjected to the pressure that will eventually turn it into a hard material like coal. Oil and gas is formed from the remains of tiny plants and animals that lived in the warm seas. As they died they were buried and squeezed into oil, which then collected in porous (sponge-like) layers of rock. Oil that comes up from the ground is thick and black 'crude' oil, must be refined for use. Non-renewable resources: are they running out? remains of swamp plants were first buried and squeezed to make peat as they were buried deeper, heat and pressure changed the peat to brown cool further pressure changed brown cool to black bituminous coal and finally to anthracite Figure 15.23 How coal is formed Non-renewable resources take a long time to form are in limited supply and cannot be easily replaced. Coal, ~ii and natural gas are examples of non-renewable resources. Humans are using the Earth's store of energy such as coal ' oil and natural gas faster than it is being formed. non-renewable resources: a natural source of limited supply .e Figure 15.24 Coal mining e Topic 15 The relationship of the Sun to the Earth Unit 1 The Earth- Moon relationship In Grade 4 you learnt that the Moon is a ball of rock in space, and that the Moon is smaller than the Earth. You were shown that the Moon is closer to the Earth than to the Sun. Figure 16.1 The Moon is smaller than the Earth. It is held in position by the Earth's gravity. In Grade 6 you learnt that the Moon revolves around the Earth and one revolution takes about a month (about 28 days). Together, the Earth and the Moon revolve around the Sun. e• 1. Name the Earth's natural satellite. 2. Which is larger: the Earth or the Moon? Topic 16 Relationship of the Moon to the Earth - - _ _,, Plane t Earth and Beyon d I Lesson 1 natural satellite: an object in space that orbits a bigger object astronaut: a person who travels in space The position of the Moon and the Earth and the effec ts of gravity The Moon is the Earth's companion in space. The Moon revolves around the Earth continuously, just as the Earth revolves around the Sun. The Moon is the Earth's natural satellite. The Moon is about a quarte r of the Earth's size. The Moon's gravit y is only a sixth of the Earth's gravity. Astronauts can jump easily on the surface of the Moon due to reduced gravity even in heavy space suits. What is gravity? Gravi ty is the force that holds the Universe together. It is the force that keeps the Earth in once piece, keeps us on the ground, plane ts circling the Sun, and the stars togeth er in their galaxies. In fact, every bif of matte r in the Universe has its own gravit ationa l pull and attrac ts every other piece of matter. The streng th of the pull depends on: the mass of objec ts • how far apart the object s are, the distance between them. • Objec ts with a high mass are called f!lassive . object s. Massive objec ts exert a strong : gravit ationa l pull on light objects. Objects that are far away exert little pull on each other. nd th e The more matte r there is in something, a th th closer its partic les are packed toge er, e strong er the gravitational pull. Figure 16.2 The Moon is the Earth's natura l satellite, it orbits the Earth continuously. • -r~nic 16 Relatio nship of the Moon to the Earth The Sun is a very large star and it is the Sun's force of gravit y that holds the plane ts in their orbits . orbit: to circle; the curved course followed by a heavenly body The Earth's gravit y keeps the Moon in its orbit. The Moon, as you learnt earlier, is much smaller than the Earth and therefore has a much lower force of gravity. This explains why astron auts on the Moon's surface are able to jump up high with very little effort. -~ / \ Figure 16.4 Gravity pulls objects toward s the centre of the Earth. Grav ity - stops us from falling off the Earth Gravi ty is the force that pulls towar ds the centre of the Earth. No matte r where you stand on the Earth's surface, the ground is alway s down. So, no matte r where you are on Earth, all objec ts fall towards the ground. The force of gravit y depends on the mass or amou nt of material of an objec t - objec ts feel heavy because of their mass. Isaac Newton realised that gravity not only affect s the Earth, but also controls the movement of the planets and the stars, as well as the orbit of the Moon around the Earth. .,, .,,... ~I Figure 16.3 Buzz Aldrin walking on the Moon in 1q6q. This picture was taken by Neil Armstrong. --3Earth ... ... ... ''QI \ I I \ \ I \ ~ ~Mo on \ I \ I \ I ' ~ Orbit of Moon arou nd~' ~r Earth takes 1 month ~ ' •, . --- --~ --/ . Figure 16.5 The Moon revolves around the Earth in a circula r orbit. O • T9pic 16 Relationship of ~he Moon to the Earth _ l Planet Earth and Beyond spring tides: the large high tides, with lower low tides in beween, are produced twice each month when the Sun and Moon are in line so that their gravitational pull is combined neap tides: the small-range tides that occur when the Sun's gravitational pull and the Moon's gravitational · pull are not reinforcing each other Lesson 2 Tides If you spend a full day at the sea you will notice the rise and fall of the level of the ocean caused by the tides. Tides are the daily rise and fall of the levels of the sea. At places along the coast, the' level the waves reach along the beach rises and falls twice during a day-night period (24 hours), as the tide comes in (flows) and goes out (ebbs). When the level of the ocean surface is up, we say that the tide is in - it is high tide or flood tide. When the level of the sea starts dropping, the tide is said to be going out - it is ebb or low tide. If you stay longer than just one day at the sea you might notice something else: the tidal range - the difference between high and low tide - is constantly changing. Twice each month the water reaches a maximum height, and these large tides are called the spring tid~s. Halfway through the monthly cycle the range is _much smaller, and these weaker tides are called neap tides. What is not so obvious is that the tides are caused by the gravity of the Moon. Gravity is the force of attraction that always tries to pull two objects together. The Sun's huge gravitational force keeps the planets in their orbits. Earth's gravitational pull keeps us safely on the Earth's surface. The Moon, too, exerts a pull on the Earth. It has little effect on solid rock, but it does have a very great effect on the water of the Earth's oceans. • Topic 16 Relationship of the Moon to the Earth 2. Demonstrate the pull of gravity by swinging a ball attached to a rope in a circular movement. Tie a rope securely around a soccer ball. Holding the end of the rope tightly, sloV'l(IY swing the ball around in the way shown in the diagram below. (Make sure that nobody is in the way when you swing the ball.) Just as the soccer ball does not go off in a straight line because it is being held by the rope, so too the Moon travels around the Earth in a circular fashion due to the the Earth's gravitational pull. The pull of the rope (towards your hands) is like the Earth's gravitational pull inward towards the centre of the Earth. ~ .;,. . ~ . space probe: satellites designed by . space scientists and engineers for travel in space Figure 16.7 Boy swinging soccer boll attached to rope . - .. . f Cool fact: t · · Space probes rely on gravity to pull them in towards l planets. However, for a·safe landing they·must f slow down their descent by using a parachute. This . . I t wo~ld only work for sm~II planets; the gravitational · pull bf massive planets like Jupiter i·s too great for a paracliute to have -much effect; " l O• Topic 16 Relationship of the Moon to the Earth Figure 16.8 Space . probes rely on gravity to pull them towards the planets. Earth -----· '. 0: I ?l> '--- pull of Sun '--- pull of Moon Moon Sun pull of ~-~n ~:~ Earti'l-- ... '~? \ / pull of Moon '~ - Moon Figure 16.q Tidal ranges ore usually small in mid-ocean but can be very large where tidal waters ore funnelled into a boy or up a river mouth. Figure 16.10 The Moon is in line with the Sun at Full Moon and New Moon. The Sun and Moon both exert a pull on the oceans, but even though the Sun is 27 million times heavier than the Moon, it is so far away that its pull is much weaker. However, it still has an effect on tides. When the Sun, Moon and Earth are in line, their con:,bined gravitational pull produces very high and corresponding very low tides called spring tides. The Moon is in line with the Sun at full moon and new moon. When the Sun and the Moon are at right-angles to each other the difference in pull is less obvious and we get much smaller, lower high tides and higher low tides called neap tides. This happens when the Moon is in its first and third quarter phases. centrifugal force: when an object, which is moving around a central point, appears to be moved away from the centre by another force As the Moon travels round the Earth, it pulls the water on the side of Earth nearest to it outwar ds into a bulge. A similar bulge forms on the opposite side of the Earth. This is caused by the water being thrown outwar ds by the Earth's spin, caused by centrifugal force that results from the Earth's rotation. These two bulges travel round the globe, produc ing the two high tides each 24 hour period. If the Earth was covered only with wat~r and the Moon's orbit was directly above the Equator, the tides would be the same all over the world. It is however, not that simple. The oceans are trapped between odd-sh aped landma sses and their basins are broken up by mountain ranges similar to those found on Earth's land surface. Even the Earth's spin affects the way the water moves as it sloshes about. The result is that tides can vary enormously from place to place. In addition, because the Moon's orbit carries the water a long way to the north and south of the Equator, its pull is lopsided, making one of the daily high tides bigger than the other. Figure 16.11 Tides ~ . • Topic 16 Relationship of the Moon to the Earth - ~ V Ecosystems on a shoreline What is a shoreline? The place where the ocean, sea or a body of water meets land is called a shoreline. The shore is the land between the high and low tide water marks. This area along the coast contains unique ecosystems which are able to thrive even though they are subject to fluctuating tidal water levels on a daily basis as well as high levels of salinity. Ocean shoreline ecosystems are tiome to plants and animals that have had to adapt to surviving in its salty, sandy environment. There are several types of shoreline ecosystems, such as sandy shores, mud flats, salt marshes, mangrove forests and tidal pools. Many animals can be found on a shoreline, including sea stars, crabs and insects. Animals living on shorelines adapt to changing tides by burying themselves in the sand during low tide, where they stay until the tide returns. Plant life in shoreline ecosystems varies considerably, ranging from sea oats to mangrove trees. Some shoreline ecosystems such as those in the iSimangliso Wetland Park which is situated on the East Coast of Kwa-Zulu~ Natal, are home to pristine natural ecosystems, ranging from coral reefs and sandy beaches to dune forests and wetlands. Animals include the leatherback and loggerhead turtle that rely on the tides to beach them on the sandy shore so that they can lay their eggs. -~ Rgure 16.12 iSimangliso Wetland Park e e Topic 16 Relationship of the Moon to the Earth 0 t, 1 I \ in a circular tevolves around the.Earth Moorr The .. . . ·· path calle·d 01'.l orbit. . . . · . · • · · All object; eXertJt;gr.ovitotion~l-_pull. ·· s on Qnal purl of ·an object depend_ • · The·grav~tati_ the ITlass·qf. the object.-'·sig qbjects exert more • ~ \ ·· . gravitcitionq!;,p411 thci(l ~rJ!all8r obj~ct_s. ...· . • The greaJei't.h~ di;tqK~iJk~t}!Veen obje¢tS, the less effe·c t the.:grbvitqtiQn~1-~~·w1f ·:<_.·_.·,. :. <_ ·_:_, ·. ·_ . C _.- : • _· Th8 Eaitf s gro~ilati9~0J}~~U;l'JqltJslhe M6on in its · orbit. ·· · --_ ·,:·-.._ .:-."·:·•:/£·:? -~</: ..· ·_-. · · :·• • , • • • • • ' ◄ ◄•· ,..... ·, ' • • -~' • ':-- • The Mo6ri -has its.6Wn;:gr,Qvity~ _which is much weaker than thdt:of the~·Earth - becdu·s·e. it is-so ·much smaller. gravitational pull of ·ocean tides are-caus~.d b.y· .' the Sun·-and the -Moon oii the .Earth. · Tides are predictable and 'repeat at regular intervals. Two high·:and two low tides are experienced -at _coastal places on Earth over a 24 hot1r ·period. Extra •high high tides-and extra ·1ow·low tides are called spring tides. · tidal range is small are called neap re the _ Tides whe_ tides. - • • ' •~ • ' . • I t• ,• ... ' t.~e • ~