Activity type Activity 2.3 Plates on the move
The surface of the Earth In 1912 Alfred Wegener, a German meteorologist, published a small is like a thin, hard crust book ‘The Origin of the Continents and Oceans’. He proposed that the floating on a denser Earth’s crust is divided up into many plates. These plates appear to layer of semi-molten rock float and move across the Earth’s surface. All the plates are moving. (the asthenosphere or This movement has completely changed the appearance of the Earth’s upper mantle). surface over geological time. It also explains many phenomena related to the distribution of flora and fauna, geological patterns around the world, and the formation of the world’s great mountain ranges. It took Alfred Wegener (1880 – 1930) almost 50 years for his theory to be widely accepted by the scientific world. Today it is one of the foundation ideas of geology.
The crust is cracked FOSSIL EVIDENCE FOR into several sections PLATE TECTONICS. called tectonic plates. These float on the semi-solid mantle The locations of certain below and move slowly over long fossil plants and animals periods of time. This process is called on widely separated continental drift. Australia sits on the continents would form Indo-Australian plate, which is the definite patterns if the fastest moving plate on Earth. We continents were re-joined are drifting northwards at a rate of (as shown by the bands of around 6 cm/year. colours).
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The RING OF FIRE shows the boundary of the Pacific Plate. It is the largest tectonic plate on Earth. It is having a rough time at the moment. As it slowly (but quickly in geological terms) moves towards the north west it is colliding and grinding past several other plates. The result of these violent interactions is the Ring of Fire.
? What does the Ring of Fire surrounding the Pacific Ocean tell us about what is happening beneath the Earth’s surface?
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TYPES OF TECTONIC PLATE BOUNDARIES A CONVERGENT BOUNDARY occurs where one plate is pushed beneath another. These often happen near the edges of continents. When these occur in the middle of an ocean there are often islands created. Can you find an example of this near Australia using the map provided on the previous page?
A DIVERGENT BOUNDARY occurs when two plates pull apart. Most happen in the middle of oceans and are called mid-ocean ridges where new ocean floor is made. Can you see on the previous page a divergent boundary that is not in the middle of an ocean? When a divergent boundary occurs on land it is called a continental The Himalayas and the Andes are rift boundary. There is one of these two of the world’s mightiest mountain currently forming in north Africa. It ranges. They are both the result of is called the Great Rift Valley. a collision at convergent boundaries TRANSFORM BOUNDARY between tectonic plates. These A mountain ranges are quite young. The Himalayas (or conservative boundary) occurs The Andes when two plates slide past each The Himalayas began rising around other; e.g. the San Andreas fault in 50 million years ago, and the Andes Click here to learn more about the structure of the Earth California. around 30 million years ago. and how tectonic plates have moved over time.
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