1- Water on Earth 2- Oceans and seas / continental waters 3- Uses, risks and problems of water

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1 Contents: I- Relief 1- Structure of the Earth and relief formation 2- Shaping of relief 3- Types of relief II- Water 1- Water on Earth 2- Oceans and seas / continental waters 3- Uses, risks and problems of water Unit 2- Relief and water on Earth Now you all know what Geography is and what its purposes are, we can start the study of our planet. To start with, we are going to analyse the Geosphere, that is to say the relief and landforms of the Earth. In the second part of this unit, we will investigate the Hidrosphere, in other words, the water of our planet in all its forms. As a result, we will have a whole description of two of the three main parts of the Earth, and it will only leave the study of the Atmosphere to complete this issue (unit 3). However, it is also time to face one of your more awful nightmares concerned with Geography: studying the physical maps. But don t worry, we are going to begin with an easy one, the World map, only for remind what you already know. The other maps will be studied in unit 4. I- Relief 1- Structure of the Earth and relief formation Do you know what the theory of tectonic drift 1 is? Probably not, but if I say to you that 350 million years ago there was only a big continent called Pangaea (literally all the Earth), you would tell me that you already knew it. A scientist named Alfred Wegener was the author of this theory one century ago, claiming that in the past there was just a huge continent (Pangaea) surrounded by one big ocean (Panthalassa). The internal forces of the Earth broke this continent and so during the past 150 million years our world has been changing until its present distribution. That is the reason why if you 1 Deriva continental 1

2 stare at a world map you may say it is like an enormous jigsaw puzzle. In order to understand this process we have to remember how the internal structure of the Earth is. In other words, we must know how the Geosphere is divided: As you can see, the Earth is divided into three different layers: 2

3 - The inner one is the core or endosphere; - The second layer is the mantle, the biggest one and composed of magma (molten rocks) which can be ejected by volcanoes (lava); - The outermost layer is the crust, which is divided between the continental crust and the oceanic crust. Moreover, the lithosphere (the rigid crust and upper mantle) is divided in tectonic plates which are floating on molten rocks in a very slowly movement. Both oceanic and continental plates are constantly producing movements of collision and separation, and that is the reason why the continents have been travelling during the past, and still go on. Watch this video and figure out how the Earth is thought to be in the future: But, how is it possible that these tectonic plates could be moving constantly? Stare at this picture: As you can see, magma is coming up to the surface from inside the Earth through a fissure called oceanic dorsal, which actually is the separation between two oceanic plates. This way, the Earth is creating new land constantly and moving the plates. However, some of these plates are colliding, and that is the place where the crust disappears, creating deep ocean basins and forming the great mountains of the world. 3

4 These collision and separation movements also create faults where earthquakes and volcanoes are usual, and it is the reason why some places are constantly affected by these phenomenons. Let s watch these video: The subduction movement is the origin of some of the biggest earthquakes we have known, even reaching the nine points in the Richter scale! And now, why don t we watch this video to summarize all this information? 2- Shaping of relief Now we know one important thing: the relief of the Earth is constantly changing, although we may don t notice it. Actually, the relief is made up by internal forces (plates tectonic, earthquakes, volcanoes, etc.) and by external forces which shape the natural forms. We have learnt something about the first ones, although we can say something else. For example, the process which creates mountain ranges and landforms is called orogenesis, and it is the origin of the big mountains of the world (folding the Earth s surface), the volcanoes and the fault- block where earthquakes are usual. You only have to take a look at the world map and you can realize that the biggest mountains have been lifted by the collision of two tectonic plates. Fault block diagram Watch carefully this video and try to understand how an earthquake is formed. As you can see, these enormous forces have been shaping our planet since the beginning of time, but there are other agents which are transforming the shape of our planet, the external agents. We can find three external agents which are water, wind and living beings (leaving apart the human action over the Earth s surface). All these agents 4

5 produce erosion, transportation and deposition which constantly are creating new landscapes, sometimes in a very particular way (just think about the Pedriza). Water is a fundamental agent in these processes, sometimes eroding itself the land (rivers, seashores or glaciers) or combined with others agents (freezing or oxidizing the rocks). Moreover, it is necessary for the plants and animals which create the biological erosion (roots, dens, etc.). 3- Types of relief Therefore, we have seen the main internal and external agents which create the different types of relief of our planet. Now it is time to learn something else about them, and we are going to begin with the continental and costal reliefs. You probably already know that emerged land is only a quarter of the whole crust of the Earth, but you must know that even under the sea we can find the continental shelf, so the border between land and sea is not so clear; in fact the continental land reaches some kilometers offshore until the continental slope. In this picture you can see the main land and costal forms: All these relief forms are so common that you probably know examples of all of them, so you have to add these words to your geographical vocabulary! As you can see, these forms are produced by the combination of internal and external forces, being the erosion, transportation and deposition the origin of many of them. On the other hand, we can find the ocean relief quite boring because the lack of diversity in its forms. The reason is that the ocean ridges are constantly creating new soil which is barely modified. In fact, the bottoms of the oceans basins are large plains (abyssal plains) at a depth between 3 and 6 kilometers. The ocean trenches are located in the subduction zones between two tectonic plates, reaching the deepest areas of the world. In the areas where this relief touches with a continent, we can find the 5

6 continental slopes (a big and steep precipice of several kilometers) and the continental shelves, flat areas of 300 meters depth that reach the cost and very rich in living beings). II- Water on Earth 1- Water on Earth Look carefully at this graphic and think about it. As you probably know, planet Earth is also known as the blue planet because 75% of its surface is water. But, does it mean that mankind can use this resource with no limits at all? Actually, the access to water is a big problem for several hundred of millions people every day, and it is considered to be one of the main causes for future wars. If we only consider the fresh water (3% of water on Earth), we can notice that the accessible water is so scarce that we must keep it unpolluted and use it responsibly. However, if we take a look at the main rivers, lakes and aquifers we realized that it is not always a reality. Therefore, we are going to separate the study of water on Earth in two main topics. First of all, you are going to learn about the oceans and seas and the continental waters. After that, we will discuss about the risks and problems that affect this issue. 2- Oceans and seas / continental waters Now we know that only a few water on Earth is fresh. However, salt water is hugely important for humankind. For example, ocean currents can determinate the climate of our planet (Do you know something about El Niño?). And don t forget that cold currents are essential for fishermen all around the world. 6

7 The main characteristics of sea water are salinity, density and temperature, and this produces the differences between the seas on Earth. Moreover, sea water has different movements. On the one hand, there are waves produced by wind that erode the seashore constantly, modifying the landscape. On the other hand, there are periodic high and low tides produced by the gravitational pull of the Moon and Sun, which can be used to obtain energy. In the end, there are ocean currents with different salinity and temperature that move around the seas like rivers (Do you remember Nemo?). Cold currents born in the poles and produce dry weather (West coast deserts) and low temperatures. Hot currents cause higher temperatures and wet weather because of the evaporation, and are originated in the equatorial zone. To sum up, we can say that sea currents are the heating of the Earth, and if the climate change modifies these currents (as it seems to be happened), weather disasters would be more usual. Continental waters Although continental waters are only the 3% of the whole water on Earth we must study its multiple forms and the multiple ways we need them for (drinking water, irrigation, fluvial travelling, etc.). The first kind of inland water we can find are rivers, with enormous diversity of flow rate and length, but vital for human societies. Rivers can be tributaries if they flow into other rivers, and sometimes they can disappear in dry seasons, but usually all of them have the following parts: - Upper course, where we can find the source of the river, with a little flow rate but big erosion. 7

8 - Middle course, where tributaries join the main course. The stream transports sediments that create rich valleys for agriculture. - Lower course, where we can find the wider channel and the water moves slowly so it deposits sediments that can create deltas in the river mouth. In any case, big rivers always produce the creation of big cities and civilisations, such as the Egyptian, because of the possibilities of irrigated agriculture and travelling through the river. Something similar happens with lakes and ponds all over the world, very important for the economy of societies that live nearby. Other forms we can find inland waters are underground water, which can be found in aquifers all around the world and it can be extracted through wells, and glaciers, today disappearing of many mountains of the world because of the climate change. the rivers create V valleys. As you can see in this diagram, a glacier is just a river of ice that create a big cirque basin in the summit of the mountain; the tongue goes down the mountain eroding the rocks and creating a valley that forms a U, as 3- Uses, risks and problems of water Throughout this unit we have seen some of the uses that humanity has made of water. Do you remember any of them? Nowadays agriculture, fishing, merchandise and many other activities use the rivers and seas, and even the UNESCO calculates that 75% of people will live near the costs in Even mining and energy industries are looking to the oceans as a new source once the inland ones are running out. This increasing pressure over the water sources of the planet is producing both flood disasters and water scarcity, as long as the climate change is affecting the weather in the Earth. Moreover, pollution is hugely affecting to rivers, lakes, aquifers and seas, so some of them cannot be used for fishing or irrigating crops. 8

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