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Name: ANSWER KEY A Journey on the Ocean Floor (Starting on page 41 of the Text Book) The features of the ocean floor contain mountain ranges, steep valleys, and vast plains. Not only that, but all of these features under the ocean tend to be much larger than the similar features on land. Label the following diagram of the ocean floor using the list of words given below: Continental Shelf, Continental Slope, Abyssal Plain and Mid-Atlantic Ridge The greatest influence in shaping the ocean floor is the movement of the Earth’s crust through the tectonic processes. When two plates are pushed apart, the underlying magma oozes up and quickly hardens, and forms long, undersea mountain chains called ocean ridges. These ridges are the youngest areas of the sea floor and are still being formed by volcanic eruptions underneath the ocean. With each new eruption, the new material pushes the tectonic plates further apart. Chain of Volcanoes also called a “ridge”. In the illustration to the left, indicate the location AND name of the feature created when two plates are forced apart by the upwelling of Magma. At some point, the plates moving apart from the mid-ocean ridge must come in contact with other plates. When two plates collide, the smaller plate is forced to bend steeply down beneath the larger dense plate. When this happens, this a trench is formed. One of the deepest trenches is called the Marianas Trench. It extends 11 km below sea level. Between the high mountain ranges at the centre of the basin and the deep trenches at their edges, the ocean floors are very flat. These wide, open features of the deep sea are called abyssal plains. They are formed of thick deposits of sediment, up to 1 km deep in places. The sediments come from the continents, brought to the ocean by rivers. They reach the sea floor by great underwater landslides that can be either started by earthquakes, or simply by the force of gravity. Questions 1. Scientists speculate that most of the water that originally formed the oceans several billion years ago came from two different courses. List these two sources: (i) Comets (ii) Volcanoes 2. What are the wide, flat areas of the ocean basin called? Abyssal Plain. 3. What is the name of the ocean floor where two tectonic plates are moving apart? Ridge or a chain of volcanoes. 4. How did the continents move into their current location? This is due to the movement of the tectonic plates. The magma in the mantle moves the plates, which in turn moves the continents which are held by the plates. 5. Explain how erupting volcanoes contributed to the formation of oceans? 1. Volcanoes helped to provide water to the early Earth by producing gases (oxygen and hydrogen) which formed water. 2. When volcanoes form from the hardening of magma, they push the continents and plates apart helping to form a “sink” called an ocean basin. Over time, this makes the ocean basin bigger and also helps to change the features of the ocean floor. 6. Briefly describe the following feature of the ocean floor and explain how it formed? Ocean Floor Features Ridge What does it look like? How is it formed? The upwelling of magma from the mantle, which squeezes through the plates and hardens.