Werkstuk: Earth
Introduction:
The Earth's crust is really thin. If you draw a line it will still be too thick to be in scale. The crust differences under continents and under oceans. Under the continents it's about 35 km thick and this crust is made up of mostly basalt rock, made of silicate (SiO rich crystalline rockformations), and is rich in iron (Fe) and magnesium (Mg). Under the oceans, the crust is about 5 km thick and this crust is made up of SiO poor crystalline rockformations, which evolved from recycling of basaltic oceanic crust. So actually, the crust we live on isn't as strong as we all think. It is too thin for the measures of our Earth and not strong enough to resist the pressure of our Earth's mantle. The mantle of the Earth is about 3000 km thick and exists of a thick liquid stonelayer, just underneath the Earth. The metallic core has a liquid outer portion and a solid inner part. The pressure of the core is much bigger than the atmospheric pressure. The crust is made up of segments, which are known as plates that move about slowly. Over millions of years, these movements changed the architecture of the continents as the plates interact. These plates are constanually being created and destroyed, but the rates of creation and destruction are very high for oceanic plates and very low for continental plates.
Continental drift:
The shapes and sizes of the continents have never been the same. They are continually changing, although it happens really slow. It is known that they move a few centimetres a year. In 1915 a book over drifting continents, was published by Alfred Wegener. The book was about an ancient "supercontinent" that scientist called Pangaea. This "supercontinent" consisted of what we now call Africa, South America and North America. When Pangaea started to break up some 300 million years ago, Africa wasn't connected to North America anymore forming two continents, called Laurasia and Gondwanna. Later, these two continents started to split up as well, because the Atlantic Oceans began to grow in the place where Africa split away from South America. After some thousands of years they became Africa, Europe, South America and Asia. It seems that the Earth's processes continually either split supercontinents apart or move them together, a cycle that takes hundreds of years.
It also happens that two continents started to move towards each other. They started to press against each other, meaning that some parts started to crumble away and that the borders of the plates were pushed up making mountains. Because of the congestion of hot mantle material, the ocean floor in the middle of the oceanic ridges, will be broken and will be pushed away from eachother. The into existing coming crevice will directly be filled up with hot mantle material that clots and new rockformations form. The first stage of this process is visible in the big African Gully. In the far future Africa will be split into two continents. The warmth needed for this congestion of hot mantle material is probably descended of the falling apart from radioactive elements in the Earth's mantle.
What happened?:
Forty years after Alfred Wegener put forward his controversial continental drift theory, technological advances revealed a great deal of information about the ocean's floor. Two research scientists, called F. Vine and D. Matthews, suggested in 1963 that the ocean was made up of younger rock than the continents. This let to the all-embracing theory of plate tectonics, which divides the World into plates, made up of partly ocean and partly continents.
Oceanic plates are being created along massive rifts. Materials (magma) well up from within the Earth along these rifts. If under an ocean, the materials add to the oceanic plate spreads from the rift zone. If under a continent, the rifts may crack the continental plate(s) under which they form, causing the continental plate(s) to spread from the rift. Once the opening rift connects with a current ocean, a new ocean forms as the pieces of continental plate spread and the rift area is filled with water. Under the ocean surface, mountains from as further magma rises from within the Earth. The ocean plate continues to expand. The area where plates are moving apart is called a zone of divergence. While some plates are expanding, the others must undergo destruction. Areas in which plates are undergoing destruction are called zones of subduction. The oceanic material is being pushed into the Earth and is remelted. As the ocean plates expand, the continental plates are separated. Both types of plates are drifting. Driven by the pressure of the expanding ocean plate, mountain building occurs as these plates crash into other plates. The lava of the mantle is continuously moving and has a reaction on the plates. This is how, what we call "the continental drift", happens.
Evidence supporting the theory of continental drift:
Evidence that proves Continental drift is true and not merely a theory, can be divided into two general continents. The studying of fossils from different periods in the Earth's history is one of these categories. The other category is the studying of rocks and other geographical features and occurrences.
Fossilised remains of the same breed of dinosaur have been found on different continents. An example of this being that fossils of a dinosaur called Mesosaurus were found on both sided of the Atlantic Ocean, in South America and Africa, but absolutely not in any other location. If the continents did not actually drift, as the theory suggests, then it would have been necessary for the dinosaurs to swim from one continent, across the Atlantic in order to reach the other continent. The Atlantic Ocean is however to big for even a dinosaur to swim. Another example is the dinosaur Lystrosaurus, of which fossils were found in both Antarctica and South America. The current climates in these two places are entirely different, which therefore suggests that Antarctica and South America must have once been joined together. This piece of evidence suggests that the continents South America and Africa were joined together and have since the time of the Mesosaurus, split apart, and drifted away from each other. Just as the fossils of the same dinosaurs have been found in different parts of the world, so too have the fossils of plants. The same species of plants have been found on opposite sides of the oceans. If the theory of the Continental Drift is not correct and the continents on the Earth's surface have always been in the same location that they are now, then the following examples would not have been possible. If the theory is not correct, then it would have been necessary for the seeds of the plant on one continent to have been carried by the wind, across the ocean, to another continent. But it is simply not possible for seeds to be carried so far. This therefore means that at one time, the continents must have been joined together, enabling the plants to grow together. When the continents broke apart, the plants eventually died and were fossilised at different parts of the Earth. If this alone is not enough evidence, the fact that some of these fossilised plants were found on continents with a cold climate should be. These plants would never have survived in such cold climates and this proves that either the climate of the Earth has changed drastically, which is not very likely or that the continents have drifted apart, to parts of the world with different climates.
When the geologists study hardened basalt, the iron within it points to where the Magnetic North Pole was hardened. As molten rock has erupted from inside the Earth almost ever since it began, the hardened Basalt that the geologist have examined have dated from several million years ago, to over 300 million years ago. It has been found out that the iron, in the most recent specimens of Basalt indicates that the Magnetic North Pole was in an area that we now call the Arctic Circle. The older Basalt, however, shows that the Magnetic North Pole was somewhere on the Antarctica continent. We know that it is not possible for the Magnetic Poles to move so drastically and that the North Magnetic Pole could once have been somewhere on Antarctica. This therefore means, that the continent of Antarctica must once have been in a completely different location, thus proving that the continental drift is a fact. When we studied the rocks around the world it showed that glaciers were once in the places where we would now not think possible. One such a place where glaciers have been found to exist, is the Sahara Dessert in Northern Africa. This place is very hot, with little water, not the place most would expect to have found glaciers. The fact that there were once glaciers here suggest that one of the two things are true. Either million years ago the continents of the Earth were in the same position as now and that the climates were totally different. Or that the climate was pretty much the same as now and the continents were in different positions, with the Sahara Desert being located on one of the poles.
Conclusion:
The continents have once been connected to each other, but after some millions of years they moved apart. Once they will move back to each other again. This is proved by the studying of rocks and by fossils of plants and dinosaurs, which were found Antarctica, South America, Africa and on both sides of the Atlantic Ocean. It is a never-ending cycle.
List of literature:
CD-ROM: Encarta '98
Publisher: Microsoft
CD-ROM: Word '97
Publisher: Microsoft
Book: Wetenschap voor de jeugd
Publisher: Seam Junior
Book: Junior weet en kijk boeken Part: Jij en de aarde
Publisher : Lekturama
Book: Geofinale hv
Author: B. Tolner m.m.v. E.C Pierhagen en J.C. Smits
Book: Eyewitness science Part: Earth
Publisher: Dorling Kindersley Limited
Book: De aarde, wonderlijk en geheimzinnig Part: Meesterwerken van de natuur Publisher: Reader's Digest
Book: Adembenemende Natuurwonderen en Fascinerende Landschappen
Publisher: Reader's Digest
Book: Wist u dat?
Publisher: Reader's Digest
Book: Geheimen van moeder aarde
Publisher: Lekturama
Book: Schatten van de aarde Part: Geschiedenis van de aarde
Publisher: De Agostini
Internetsites:
http://www.uni-kassel.de/~roehing/welcome.html
http://www.chem.wsu.ecu/phs298/288-ContPlate.html
http://www.masw.nodak.eud/hssdiw/mearte/notes/cdrift/htm
http://www.infoplease.lycos.com/ipa/A0004440.html
http://www.dev.onfoplease.com/ipa/A0001745.html
http://kids.nasa.gov/archive/Pangaea/evidence.html
The Earth's crust is really thin. If you draw a line it will still be too thick to be in scale. The crust differences under continents and under oceans. Under the continents it's about 35 km thick and this crust is made up of mostly basalt rock, made of silicate (SiO rich crystalline rockformations), and is rich in iron (Fe) and magnesium (Mg). Under the oceans, the crust is about 5 km thick and this crust is made up of SiO poor crystalline rockformations, which evolved from recycling of basaltic oceanic crust. So actually, the crust we live on isn't as strong as we all think. It is too thin for the measures of our Earth and not strong enough to resist the pressure of our Earth's mantle. The mantle of the Earth is about 3000 km thick and exists of a thick liquid stonelayer, just underneath the Earth. The metallic core has a liquid outer portion and a solid inner part. The pressure of the core is much bigger than the atmospheric pressure. The crust is made up of segments, which are known as plates that move about slowly. Over millions of years, these movements changed the architecture of the continents as the plates interact. These plates are constanually being created and destroyed, but the rates of creation and destruction are very high for oceanic plates and very low for continental plates.
Continental drift:
The shapes and sizes of the continents have never been the same. They are continually changing, although it happens really slow. It is known that they move a few centimetres a year. In 1915 a book over drifting continents, was published by Alfred Wegener. The book was about an ancient "supercontinent" that scientist called Pangaea. This "supercontinent" consisted of what we now call Africa, South America and North America. When Pangaea started to break up some 300 million years ago, Africa wasn't connected to North America anymore forming two continents, called Laurasia and Gondwanna. Later, these two continents started to split up as well, because the Atlantic Oceans began to grow in the place where Africa split away from South America. After some thousands of years they became Africa, Europe, South America and Asia. It seems that the Earth's processes continually either split supercontinents apart or move them together, a cycle that takes hundreds of years.
It also happens that two continents started to move towards each other. They started to press against each other, meaning that some parts started to crumble away and that the borders of the plates were pushed up making mountains. Because of the congestion of hot mantle material, the ocean floor in the middle of the oceanic ridges, will be broken and will be pushed away from eachother. The into existing coming crevice will directly be filled up with hot mantle material that clots and new rockformations form. The first stage of this process is visible in the big African Gully. In the far future Africa will be split into two continents. The warmth needed for this congestion of hot mantle material is probably descended of the falling apart from radioactive elements in the Earth's mantle.
What happened?:
Forty years after Alfred Wegener put forward his controversial continental drift theory, technological advances revealed a great deal of information about the ocean's floor. Two research scientists, called F. Vine and D. Matthews, suggested in 1963 that the ocean was made up of younger rock than the continents. This let to the all-embracing theory of plate tectonics, which divides the World into plates, made up of partly ocean and partly continents.
Oceanic plates are being created along massive rifts. Materials (magma) well up from within the Earth along these rifts. If under an ocean, the materials add to the oceanic plate spreads from the rift zone. If under a continent, the rifts may crack the continental plate(s) under which they form, causing the continental plate(s) to spread from the rift. Once the opening rift connects with a current ocean, a new ocean forms as the pieces of continental plate spread and the rift area is filled with water. Under the ocean surface, mountains from as further magma rises from within the Earth. The ocean plate continues to expand. The area where plates are moving apart is called a zone of divergence. While some plates are expanding, the others must undergo destruction. Areas in which plates are undergoing destruction are called zones of subduction. The oceanic material is being pushed into the Earth and is remelted. As the ocean plates expand, the continental plates are separated. Both types of plates are drifting. Driven by the pressure of the expanding ocean plate, mountain building occurs as these plates crash into other plates. The lava of the mantle is continuously moving and has a reaction on the plates. This is how, what we call "the continental drift", happens.
Evidence supporting the theory of continental drift:
Evidence that proves Continental drift is true and not merely a theory, can be divided into two general continents. The studying of fossils from different periods in the Earth's history is one of these categories. The other category is the studying of rocks and other geographical features and occurrences.
Fossilised remains of the same breed of dinosaur have been found on different continents. An example of this being that fossils of a dinosaur called Mesosaurus were found on both sided of the Atlantic Ocean, in South America and Africa, but absolutely not in any other location. If the continents did not actually drift, as the theory suggests, then it would have been necessary for the dinosaurs to swim from one continent, across the Atlantic in order to reach the other continent. The Atlantic Ocean is however to big for even a dinosaur to swim. Another example is the dinosaur Lystrosaurus, of which fossils were found in both Antarctica and South America. The current climates in these two places are entirely different, which therefore suggests that Antarctica and South America must have once been joined together. This piece of evidence suggests that the continents South America and Africa were joined together and have since the time of the Mesosaurus, split apart, and drifted away from each other. Just as the fossils of the same dinosaurs have been found in different parts of the world, so too have the fossils of plants. The same species of plants have been found on opposite sides of the oceans. If the theory of the Continental Drift is not correct and the continents on the Earth's surface have always been in the same location that they are now, then the following examples would not have been possible. If the theory is not correct, then it would have been necessary for the seeds of the plant on one continent to have been carried by the wind, across the ocean, to another continent. But it is simply not possible for seeds to be carried so far. This therefore means that at one time, the continents must have been joined together, enabling the plants to grow together. When the continents broke apart, the plants eventually died and were fossilised at different parts of the Earth. If this alone is not enough evidence, the fact that some of these fossilised plants were found on continents with a cold climate should be. These plants would never have survived in such cold climates and this proves that either the climate of the Earth has changed drastically, which is not very likely or that the continents have drifted apart, to parts of the world with different climates.
When the geologists study hardened basalt, the iron within it points to where the Magnetic North Pole was hardened. As molten rock has erupted from inside the Earth almost ever since it began, the hardened Basalt that the geologist have examined have dated from several million years ago, to over 300 million years ago. It has been found out that the iron, in the most recent specimens of Basalt indicates that the Magnetic North Pole was in an area that we now call the Arctic Circle. The older Basalt, however, shows that the Magnetic North Pole was somewhere on the Antarctica continent. We know that it is not possible for the Magnetic Poles to move so drastically and that the North Magnetic Pole could once have been somewhere on Antarctica. This therefore means, that the continent of Antarctica must once have been in a completely different location, thus proving that the continental drift is a fact. When we studied the rocks around the world it showed that glaciers were once in the places where we would now not think possible. One such a place where glaciers have been found to exist, is the Sahara Dessert in Northern Africa. This place is very hot, with little water, not the place most would expect to have found glaciers. The fact that there were once glaciers here suggest that one of the two things are true. Either million years ago the continents of the Earth were in the same position as now and that the climates were totally different. Or that the climate was pretty much the same as now and the continents were in different positions, with the Sahara Desert being located on one of the poles.
Conclusion:
The continents have once been connected to each other, but after some millions of years they moved apart. Once they will move back to each other again. This is proved by the studying of rocks and by fossils of plants and dinosaurs, which were found Antarctica, South America, Africa and on both sides of the Atlantic Ocean. It is a never-ending cycle.
List of literature:
CD-ROM: Encarta '98
Publisher: Microsoft
CD-ROM: Word '97
Publisher: Microsoft
Book: Wetenschap voor de jeugd
Publisher: Seam Junior
Book: Junior weet en kijk boeken Part: Jij en de aarde
Publisher : Lekturama
Book: Geofinale hv
Author: B. Tolner m.m.v. E.C Pierhagen en J.C. Smits
Book: Eyewitness science Part: Earth
Publisher: Dorling Kindersley Limited
Book: De aarde, wonderlijk en geheimzinnig Part: Meesterwerken van de natuur Publisher: Reader's Digest
Book: Adembenemende Natuurwonderen en Fascinerende Landschappen
Publisher: Reader's Digest
Book: Wist u dat?
Publisher: Reader's Digest
Book: Geheimen van moeder aarde
Publisher: Lekturama
Book: Schatten van de aarde Part: Geschiedenis van de aarde
Publisher: De Agostini
Internetsites:
http://www.uni-kassel.de/~roehing/welcome.html
http://www.chem.wsu.ecu/phs298/288-ContPlate.html
http://www.masw.nodak.eud/hssdiw/mearte/notes/cdrift/htm
http://www.infoplease.lycos.com/ipa/A0004440.html
http://www.dev.onfoplease.com/ipa/A0001745.html
http://kids.nasa.gov/archive/Pangaea/evidence.html