1 / 83

OUR OCEAN PLANET

OUR OCEAN PLANET. OUR OCEAN PLANET SECTION 1 – OUR OCEAN PLANET. REVISION HISTORY. 1. OUR OCEAN PLANET. 1. OUR OCEAN PLANET. 1.1 THE OCEAN. 1.1 THE OCEAN. 1.1 THE OCEAN. 1.1 THE OCEAN

yves
Télécharger la présentation

OUR OCEAN PLANET

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. OUR OCEAN PLANET OUR OCEAN PLANET SECTION 1 – OUR OCEAN PLANET

  2. REVISION HISTORY

  3. 1. OUR OCEAN PLANET 1. OUR OCEAN PLANET

  4. 1.1 THE OCEAN 1.1 THE OCEAN

  5. 1.1 THE OCEAN 1.1 THE OCEAN Although we refer to our planet as Earth, the most dominant physical feature of our planet is the ocean which covers more than 70% of the planet’s surface. The total area covered by ocean is about 362 million sq km (140 million sq miles) with an average depth of 3,720 m (12,200 ft). The ocean so dominates the planet and is so important to us that Earth should perhaps be thought of as the “ocean planet”. Our planet’s ocean is connected by currents and can thus be considered to be one continuous ocean. However, it is customary to divide it into 5 individual oceans, namely, the Pacific, Atlantic, Indian, Antarctic (or Southern) and Arctic Oceans. We can also further divide the Pacific and Atlantic Oceans into the North and South Pacific, and the North and South Atlantic Oceans.

  6. 1.1 THE OCEAN

  7. 1.1 THE OCEAN An “ocean” is a very large body of saltwater while a “sea” is a much smaller body of saltwater that is considered part of its closest ocean. Thus, the Coral Sea is considered part of the Pacific Ocean while the Caribbean Sea is considered part of the Atlantic Ocean. The term "sea" is often given to a saltwater area on the margins of an ocean (e.g. the Mediterranean Sea is beside the Atlantic). A sea is also often enclosed or partially enclosed by land while an ocean is on the margin of land. The difference is not entirely precise and there are exceptions to the general definition. The ocean generally looks blue because seawater does not absorb blue light from sunlight. When sunlight hits the water, the blue light is scattered in all directions making the ocean look blue. In seas or oceans that appear to be green, the colour is generally due to plants in the water. The northern Atlantic and Pacific Oceans, for example, are green near the coast because of a rich abundance of plants in the water. In contrast, the clear blue waters of the Caribbean Sea indicate the absence or reduced number of plants.

  8. 1.1 THE OCEAN The ocean covers a number of ocean basins including the North Pacific, South Pacific, North Atlantic, South Atlantic, Indian and Arctic basins. An ocean basin at the bottom of the sea is composed of numerous underwater islands, trenches, mid-ocean ridges, rift valleys and sea mounts. The sea bed may move as a result of lithospheric plate activity. Volcanic activity also occurs underwater which can cause violent land-forming activity. Earth’s highest peaks, deepest valleys, and flattest, largest plains are all in the ocean. We will explore some of the ocean’s features in the rest of this section. The ocean is not a just a large static volume of water but a highly dynamic system. Each ocean has large surface circulating currents that transport warm surface water from the equator towards the poles, and cool polar water towards the equator. These currents are called “gyres” and they travel clockwise around ocean basins in the northern hemisphere, and anti-clockwise in the southern hemisphere.

  9. 1.1 THE OCEAN Interconnected circulation systems powered by the force of the Earth’s rotation (Coriolis effect) and the Sun’s heat transports water from the surface of the ocean to the bottom of the ocean and back again. The driving force in this vertical mixing process is differences in water density – cooler deep water is denser than warmer surface water resulting in vertical mixing. The shape of ocean basins and adjacent land masses also influence the path of both surface circulation and deep mixing. At sea level, a variety of forces, such as the Sun and Moon, act on the ocean to stir and move the water. This movement can be gentle as the lapping of water at the ocean’s edge, or extremely violent with huge waves that can destroy whole swathes of coastline.

  10. 1.1 THE OCEAN

  11. 1.1 THE OCEAN 1.1.1 Plate Tectonics The Earth can be divided into three basic layers, namely, the core, mantle and crust. Plate tectonics explains the movement of the continental crust in the upper layer of the Earth. Heat and magma from the interior of the Earth rises and cools as it reaches the upper mantle. This causes movements of the Earth’s crust and shifting of large sections of the crust known as “tectonic plates”. Plate tectonics cause ocean basins, earthquakes, mountains, volcanoes and faults to form. This dynamic process, driven by the heat deep inside the Earth, is what sets the Earth apart from any other planet. It is now recognized that the surface of the Earth has at least 7 major plates and a large number of smaller ones, all floating on the partly molten layer of the mantle beneath. Some of these plates carry continents while others are purely oceanic. The areas where these plates meet are called “plate boundaries”. Different types of powerful natural phenomena occur at these boundaries depending on the type of boundary.

  12. 1.1 THE OCEAN 1. DIVERGENT BOUNDARY At a divergent boundary, plates are moving apart as hot magma rises and moves upwards to the surface of the earth. When the magma reaches the surface, it cools and solidifies to form a new crust. Imagine two giant conveyor belts, facing each other but slowly moving in opposite directions as they transport newly formed oceanic crust away from the ridge crest. This process continues over many millions of years and eventually results in the formation of an ocean basin. Examples include the Mid-Atlantic Ridge which spread apart to form the Atlantic Ocean and the Red Sea. Divergent boundaries may give rise to volcanoes and earthquakes.

  13. 1.1 THE OCEAN 2. CONVERGENT BOUNDARY At a convergent boundary, the plates move toward each other. If an oceanic plate and continental plate collide, the denser oceanic plate is forced underneath the continental plate, forming a subduction zone. As the oceanic plate is forced below the continental plate, it melts and becomes magma. The magma collects to form a magma chamber and may rise up through cracks in the continental crust. As pressure builds, a volcanic eruption may occur. When two continental plates push towards one another, the continental crust is squashed together and forced upwards to form mountain belts. This is how the Himalayas were formed. Convergent boundaries may give rise to mountains, volcanoes, faults, and earthquakes.

  14. 1.1 THE OCEAN 3. TRANSFORM BOUNDARY At a transform boundary plates slide horizontally past each other. Transform boundaries do not create or destroy land and often give rise to earthquakes and major faults but not volcanoes. A well-known example is the San Andreas Fault, which runs through the state of California in the USA. Volcanic and earthquake activity is frequent at active plate boundaries and can be extremely violent. For example, in the Pacific Ocean, the "ring of fire" is a rough ring or circle stretching from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America. It is where the Pacific Plate interacts with other plates such as the Indo-Australian and North American plates. Over 75% of the world's active and dormant volcanoes are found along the ring of fire.

  15. 1.1 THE OCEAN In the Caribbean, the island of Monserrat has an active volcano that began erupting in 1995 and it is still continuing to so today. The North American tectonic plate is subducting beneath the Caribbean plate and forming the entire Lesser Antillean Island Arc system. The island arc is a series of volcanic islands that are formed as a result of this convergent tectonic activity. In the figure below, some of the Earth's major plates are shown with dotted lines indicating the plate boundaries. An arrow indicates the direction in which the plate is moving. The “ring of fire” is also outlined with a solid line. Note that the figure is only an approximation and is not intended to be definitive.

  16. 1.1 THE OCEAN REFERENCES & FURTHER READING http://www.mvo.ms/ http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/Maps/map_plate_tectonics_world.html http://www.bbc.co.uk/schools/gcsebitesize/geography/platetectonics/index.shtml http://pubs.usgs.gov/gip/dynamic/understanding.html

  17. 1.1 THE OCEAN 1.1.2 Sea Level Sea level is the average height of the ocean relative to the land taking into account the differences caused by tides. The sea level is not constant but changes over time. 1. SHORT TERM Some short-term causes of sea level changes include: (a) Tides The tides, which are caused by the gravitational pull of the Moon and the Sun on the Earth, regularly change the sea level so that it oscillates between high tide (the highest sea level) and low tide (the lowest sea level). (b) Storm Surges Storm surge is caused primarily by high winds pushing water toward the shore causing the sea surface to rise. The wind causes the water to pile up higher than the ordinary sea level. (c) Seawater Expanding/Contracting Sea levels also change as sea water expands and contracts when ocean water warms and cools. (d) Flooding River runoff levels or flooding due to seasonal differences in the amount of rainfall can also cause changes to sea level.

  18. 1.1 THE OCEAN (e) Earthquakes/Landslides Undersea earthquakes can generate huge waves called tsunamis that can temporarily change sea level. Abrupt landslides in the sea can also change sea levels. 2. LONG TERM Some long-term causes of sea level changes include: (a) Plate Movement Sea levels can change as shifting plates cause the volume of ocean basins and the height of the land to change. (b) Glaciers Melting Sea levels can rise as mountain glaciers melt and the water enters the ocean. (c) Icecaps Melting Sea levels can rise as icecaps break off and enter the ocean. Note that the sea level rises when the ice first enters the ocean not when the sea ice melts because the ice is already displacing an equivalent volume of water. REFERENCES & FURTHER READING http://www.weatherincayman.com/tideprediction.html http://www.tide-forecast.com/locations/GrandCayman-CaymanIslands/tides/latest http://tidesandcurrents.noaa.gov/sltrends/sltrends.html

  19. 1.1 THE OCEAN 1.1.3 Sea Floor The sea floor is divided into a number of geographically distinct areas depending on depth, plate tectonic zone, and distance from the coast: 1. CONTINENTAL SHELF The Continental Shelf lies between the coast and the 200 m (660 ft) depth contour. The Continental Shelf surrounds the continents on earth but occupies only 7.5% of the sea floor. The shelf corresponds to the submerged portion of the continental crust. 2. CONTINENTAL SLOPE The downward slope of the Continental Shelf increases abruptly at the seaward edge to form the Continental Slope, which occupies 8.5% of the sea floor. At a depth of about 3,000 m (9,842 ft), the slope flattens out to a gradient of 1:100 and the beginning of the Continental Rise. 3. CONTINENTAL RISE The Continental Rise is typically a thick flattish wedge of sediment that runs from about 3,000 m (9842 ft) to 4,000 m (13,123 ft). At around 4,000m (13,123 ft) the Continental Rise levels out again to an almost imperceptible gradient (1:1000 or less) to meet the Abyssal Plain.

  20. 1.1 THE OCEAN 4. ABYSSAL PLAIN The Abyssal Plain extends from about 4,000 m (13,123 ft) to 6,000 m (19,686 ft). It is a huge flat floor of an ocean basin that is covered with a layer of sediment. It covers over 50% of the ocean area and is the single largest environment on Earth. 5. OCEAN TRENCH The deepest places on the earth's surface are known as Ocean Trenches. These trenches are like deep wounds in the ocean floor. They form when two tectonic plates collide and one subducts beneath the other, forming a depression. The deepest trench, the Mariana Trench, extends to a depth of 11,033m (36,198 ft). 6. SUBMARINE RIDGES In some oceans, narrow, elongated ridges, resembling mountain ranges on the land, rise from the sea floor as a result of plate tectonic collisions. These are called “Submarine Ridges”. Peaks of these ridges may rise above sea level to form islands.

  21. 1.1 THE OCEAN

  22. 1.1 THE OCEAN Some of the features of the sea floor are as amazing as those we see on land. For example: DEEPEST TRENCH The Mariana Trench, which is located in the western Pacific Ocean southeast of the Mariana Islands, is the deepest point on Earth. At 11,033 m (36,198 ft), the Mariana Trench is farther below sea level than Mount Everest is above it. The Cayman Trench (also known as the Bartlett Deep or Bartlett Trough) lies on the floor of the Caribbean Sea between Jamaica and the Cayman Islands. This relatively narrow trough has a maximum depth of 7,686 m (25,216 ft) and is the deepest point in the Caribbean Sea. TALLEST MOUNTAIN Mountains are generally measured from sea level, in which case Mount Everest (8,848 m; 29,028 ft) is the tallest. However, Mauna Kea on Hawaii’s Big Island rises 10,203 m (33,476 ft) from the depth of the Pacific Ocean floor. Measured from base to peak, Mauna Kea is the tallest mountain on earth.

  23. 1.1 THE OCEAN GLOBAL MID-OCEAN RIDGE The ocean ridges form a great mountain range wound around the Earth like the seam on a baseball. The global mid ocean ridge is about 64,000 km (40,000 miles) long and is the single largest topographic feature on Earth. Several smaller mid-ocean ridges make up the global mid-ocean ridge, one of the best-known being the Mid-Atlantic Ridge which runs down the centre of the Atlantic Ocean.

  24. 1.1 THE OCEAN REFERENCES & FURTHER READING http://hypertextbook.com/facts/2001/BeataUnke.shtml http://www.redcomet.org/Preview/Ces5xPrv.html http://smithsonianeducation.org/educators/lesson_plans/science_technology.html http://www.msstate.edu/dept/geosciences/CT/TIG/WEBSITES/RESEARCH/Christine_Oxenford/index.html

  25. 1.1 THE OCEAN 1.1.4 Depth Zones Scientists have divided the ocean into layers or "zones" based on the penetration of light and depths which extend from the surface to the bottom of the ocean as follows: 1. EPIPELAGIC ZONE (PHOTIC ZONE) The Epipelagic zone extends from the surface to a depth of 200 m (656 ft). The water in this zone is fairly well mixed and, under ideal conditions, sunlight can penetrate the entire zone. Temperatures in the Epipelagic zone vary with climate and season but the worldwide average temperature of the surface zone is 22°C. 2. MESOPELAGIC ZONE (TWILIGHT ZONE) The Mesopelagic Zone extends from a depth of 200 m (656 ft) to 1,000m (3281 ft). This zone is also called the twilight zone and the mid-water zone. The sunlight in this zone is extremely faint. It is in this zone that we begin to see the twinkling lights of bioluminescent creatures. A great variety of strange and bizarre fish are also found here. 3. BATHYPELAGIC ZONE (DARK ZONE) The Bathypelagic Zone extends from a depth of 1,000 m (3,281 ft) down to 4,000 m (13,123 ft). The only visible light in this region is the light produced by bioluminescent life forms. The water pressure at this depth is crushing but a surprisingly large number of creatures can be found. Sperm whales can dive down to this level in search of food. Most of the animals that live at these great depths are black or red in colour due to the lack of visible light.

  26. 1.1 THE OCEAN 4. ABYSSOPELAGIC ZONE (“ABYSS”) The Abyssopelagic Zone extends from a depth of 4,000 m (13,123 ft) to 6,000 m (19,686 ft). Its name comes from a Greek word meaning "bottomless". The water temperature of this zone is near freezing and there is no light at all. Very few creatures can be found at these depths because of enormous pressure. Most organisms found at these depths are invertebrates and include basket stars and tiny squids. 5. HADALPELAGIC ZONE (“TRENCHES”) The Hadalpelagic Zone extends from a depth of 6,000 m (19,686 ft) to 10,000 m (32,810 ft). This zone is mostly found in deep water trenches and canyons. In spite of the pressure and cold temperature, life can still be found in this zone, particularly invertebrates, such as sea stars and tubeworms, which thrive at these depths.

  27. 1.1 THE OCEAN

  28. 1.1 THE OCEAN 1.1.5 Oceans Past/Oceans Present The ocean and continents didn’t always look the same as they do today. In the past, one huge ocean called Panthalassa surrounded the supercontinent of Pangaea because of plate (tectonic) movements. Pangaea was a C-shaped landmass that was spread across the equator. The body of water that was enclosed within the resulting crescent has been named the Tethys Sea. The break-up of Pangaea took place about 180 million years ago, first into the two supercontinents Gondwanaland (to the south) and Laurasia (to the north), and thereafter into the continents we have today.

  29. 1.1 THE OCEAN The sequence of maps to the right (adapted from the USGS) shows how Pangaea continued fragmenting to form today’s ocean basins. As the plates moved apart along divergent boundaries to create new ocean basins, convergent boundaries resulted in subduction and recycling of crustal material into the mantle. The Earth's current continental landmasses formed and eventually moved to their current positions. REFERENCES & FURTHER READING http://pubs.usgs.gov/gip/dynamic/dynamic.html http://mineralsciences.si.edu/tdpmap/

  30. 1.2 WATER 1.2 WATER

  31. 1.2 WATER 1.2 WATER 1.2.1 What is Water? Water is the most abundant resource on our planet. One molecule of water is made up of one atom of oxygen and two atoms of hydrogen, which is written as the chemical formula H2O. The two hydrogen atoms lie at 105° to each other. This arrangement results in the hydrogen end having a slightly positive charge and the oxygen end a slightly negative charge. Since opposite charges attract, individual water molecules come together through a weak attraction called a “hydrogen bond”. Hydrogen bonds allow water to exist in different states: 1. Ice (Solid) When water is frozen, the molecules are held by hydrogen bonds in a hexagonal structure. 2. Water (Liquid) As the temperature rises, ice turns into water, the molecules move freely, forming and breaking hydrogen bonds. 3. Water Vapour/Steam (Gas) As the temperatures rises even further and the molecules vibrate faster, the hydrogen bonds break, the molecules are set free, and the liquid becomes water vapour. At high temperatures, water becomes steam.

  32. 1.2 WATER Water is able to change between these states by the addition or removal of heat/energy. These transitions occur naturally between the ocean, clouds and land, as we will see later. 1. Melting Melting is the process by which ice (solid) warms up and becomes water (liquid). 2. Sublimation Sublimation is the process by which water changes from a solid (ice or snow) to a gas bypassing the liquid phase. This happens in places such as the Rocky Mountains as dry and warm Chinook winds blow in from the Pacific in late winter and early spring. When a Chinook arrives, local temperatures rise dramatically. When dry air hits the snow, the snow becomes water vapour bypassing the liquid phase. Sublimation is a common way for snow to disappear quickly in arid climates. 3. Evaporation Evaporation is the process by which water changes from a liquid to a gas or vapour when heat is added to water. 4. Condensation Condensation is the process by which warm water vapour in the air cools and changes into liquid water as water droplets. 5. Freezing As liquid water cools further, it becomes a solid (ice).

  33. 1.2 WATER 1.2.2 What is Sea Water? Water is a remarkable substance as it has many unusual properties and can behave in unexpected ways. For example, it is a very good solvent and is able to dissolve many elements. Seawater is a complex solution and is composed of the following: • 96% pure water • 3% sodium chloride (common salt or halite) • 1% other elements (e.g. magnesium, calcium, potassium) Sodium and chlorine are the most abundant elements dissolved in seawater. However, it is the combination of all of the different elements and compounds dissolved in the ocean that make the ocean “salty”. Seawater has unique properties: • it is saline • its freezing point is slightly lower than freshwater • its density is slightly higher that freshwater • its electrical conductivity is much higher than fresh • it is slightly basic (or alkaline)

  34. 1.2 WATER The salt in seawater comes from eroding land, volcanic emissions, reactions at the sea floor, and atmospheric deposition. The amount of dissolved salts in the oceans does not vary greatly from place to place or from time to time throughout the ocean. However, slight differences in salinity along with larger differences in water temperature results in water masses with different densities.

  35. 1.2 WATER 1.2.3 Where Does Earth’s Water Originate? 1. Magma Primordial Earth was an incandescent globe made of magma. All magmas contain water. Water set free by magma began to cool down the Earth’s atmosphere until eventually it became cool enough for the water to stay on the surface as a liquid. 2. Volcanoes Volcanic activity kept (and still keeps) introducing water in the atmosphere thus increasing the surface and ground water volume of the Earth. 3. Comets Scientists suspect that comets made of ice may have collided with the Earth in the past, releasing their water into the oceans.

  36. 1.2 WATER 1.2.4 Where Is All The Water? All the water we will ever have is already here on Earth in one form or another (except possibly for ice-laden comets striking the Earth). Of the total supply of about 1386 million cubic km of water in the world, almost 97% of the total is saline. Of the 3% freshwater, ~69% is locked up in ice and glaciers while ~30% of freshwater is in the ground. Only 1% is readily available for drinking. Fresh surface-water sources, such as rivers and lakes, only constitute about 93,100 cubic kilometers (22,300 cubic miles), which is only 1/700th of 1% of the total water. Yet, rivers and lakes are the sources of water most people use. In considering how precious fresh water is, it is helpful to remind oneself of the following quote: "Water, water, everywhere, And all the boards did shrink; Water, water, everywhere, Nor any drop to drink." The Rime of the Ancient Mariner – Samuel Coleridge

  37. 1.2 WATER

  38. 1.2 WATER 1.2.5 Water Cycle Earth's water is constantly changing states from liquid to vapour to ice to liquid again in a cycle that has operated for billions of years and upon which all life on Earth depends. The “Water Cycle” is driven by the sun which heats water in the ocean. Some of it evaporates into the air as water vapour. Ice and snow can also sublimate directly into water vapour. Rising air currents take the vapour into the atmosphere along with water from evapotranspiration (water transpired from plants and evaporated from soil). Cooler temperatures here cause the vapour to condense into clouds. As air currents move clouds around the globe, cloud particles collide, grow, and fall from the sky as precipitation. Some precipitation falls as snow and accumulates as ice caps and glaciers which can store frozen water for thousands of years. Snow in warmer climates thaws in spring and it flows overland as snowmelt.

  39. 1.2 WATER Most precipitation falls as rain back into the oceans or onto land, where the precipitation flows over the ground as surface runoff. A portion of runoff enters rivers which transports the water towards the oceans. Runoff and ground-water seepage accumulate and are stored as freshwater in lakes. However, not all runoff flows into rivers. Much of it soaks into the ground as infiltration. Some water infiltrates deep into the ground and forms groundwater which can flow or be stored in the rocks for long periods of time. Some infiltration is close to the land surface and can seep back into lakes and the ocean as groundwater discharge, while some groundwater finds openings in the land surface and emerges as freshwater springs. Over time, all water keeps moving, some of which reenters the ocean to start the cycle again.

  40. 1.2 WATER

  41. 1.2 WATER REFERENCES & FURTHER READING http://ga.water.usgs.gov/edu/watercyclehi.html http://www.kidzone.ws/water/

  42. 1.3 ACTIVITIES 1.3 ACTIVITIES

  43. 1.3 ACTIVITIES • 1.3 ACTIVITIES • 1.3.1 Ocean • CORE ACTIVITY • (a) Find and label the world’s oceans: • Pacific Ocean • Atlantic Ocean • Indian Ocean • Arctic Ocean • Antarctic (or Southern) Ocean (b) How many oceans are there? (c) What is the difference between an ocean and a sea? (d) Why is the ocean blue? (e) Why is the ocean sometimes green?

  44. 1.3 ACTIVITIES

  45. 1.3 ACTIVITIES • ANSWERS • (a) Find and label the world’s oceans: • Pacific Ocean • Atlantic Ocean • Indian Ocean • Arctic Ocean • Antarctic (or Southern) Ocean

  46. 1.3 ACTIVITIES

  47. 1.3 ACTIVITIES (b) How many oceans are there? There is just one ocean on Earth but there are many ways to divide it. Many scientists think there are 5 oceans (Pacific, Atlantic, Indian, Arctic and Antarctic (or Southern) Oceans) while others further divide the Pacific and Atlantic Oceans into North and South Pacific and North and South Atlantic. Thus, depending on your view, there may be 1, 5, or 7 oceans! (c) What is the difference between an ocean and a sea? An “ocean” is a very large body of saltwater while a “sea” is a much smaller body of saltwater that is considered part of its closest ocean. Thus, the Coral Sea is considered part of the Pacific Ocean while the Caribbean Sea is considered part of the Atlantic Ocean. The term "sea" is often given to a saltwater area on the margins of an ocean (e.g. the Mediterranean Sea is beside the Atlantic). A sea is also often enclosed or partially enclosed by land while an ocean is on the margin of land. The difference is not precise and there are exceptions to the general definition. (d) Why is the ocean blue? The ocean generally looks blue because seawater does not absorb blue light from sunlight. When sunlight hits the water, the blue light is scattered in all directions making it look blue. (e) Why is the ocean sometimes green? In seas or oceans that appear to be green, the colour is generally due to plants in the water. The northern Atlantic and Pacific Oceans, for example, are green near the coast because of a rich abundance of plants in the water. In contrast, the clear blue waters of the Caribbean Sea indicate the absence or reduced number of plants.

  48. 1.3 ACTIVITIES 1.3.2 Plate Tectonics EXTENDED ACTIVITY (a) Find and label the following major plates in the figure below:

  49. 1.3 ACTIVITIES

  50. 1.3 ACTIVITIES (b) On which plate do the Cayman Islands reside? (c) What is the “Ring of Fire”? (d) The spreading rate of the sea floor along the Mid-Atlantic Ridge averages about 2.5 cm per yr (or 25 km in a million years). If the distance between the U.S. and North Africa is currently 4,830 km, how many years ago were they joined assuming a constant rate of movement?

More Related