Until the mid 19th century, scientists assumed that the continents were fixed in place and subjected to only vertical movements such as those motions which create mountain ranges. By the mid 19th century, when the coastlines of the Atlantic Ocean had been accurately mapped, geologists noticed that the East coasts of North and South America could be closely fitted against the West coast of Europe and Africa. Some scientists suggested that all of the present continents once formed a single, very large land mass which had split into many pieces eons ago. Two parts pulled apart to create the Atlantic Ocean. Like most scientists who propose radical new ideas, these geologists were initially ridiculed. However Alfred Wegener, a German meteorologist, did a careful analysis of the continental fit early in the 20th century. He revived the concept that the continents once formed a single land mass, which he called Pangaea. He noted "many striking similarities between the fossil plants and reptiles on the opposite coasts" of the Atlantic ocean. 1 He showed that the same formation of three layers of rock occurs in many areas of the world: a glacial deposit called tillite at the bottom, a layer composed of sandstone, shale and coal; and a basalt lava flow on top. He speculated that the layers were formed in a part of Pangaea, which later broke up and drifted apart to form some of the continents we see today. 2 Few geologists accepted this theory until two discoveries were made in the 1950s:
 | The study of paleomagnetism -- magnetism in rocks: The magnetic field of molten rock forms when it has cooled down sufficiently to pass through its Curie temperature. It preserves the direction of the earth's magnetic field as it existed at that time. By drilling a hole through undisturbed rock, the top layer will be found to be magnetized in the current direction of the earth's magnetic field. But layers underneath are found to be magnetized in alternating directions. This showed that the earth's magnetic field reverses directions every few hundred thousand years. |
| The discovery of a continuous ridge of undersea mountains in the middle of the Atlantic and Pacific oceans: Molten material from deep in the earth "heaps up to form the ridge, and it also moves out sideways from the ridge like a pair of giant conveyor belts." As it cools, it is magnetized in the direction of the Earth's magnetic field. Every few hundred thousand years, the Earth's field is reversed. This can be detected in the form of "alternating regions of normal and reversed magnetic directions symmetrically disposed on both sides of the ridge." 1 The sea floor is spreading as new material continually wells up from within the earth. "...if one were to push the continents bordering the Atlantic together (reversing the drift that is going on at present), the continents would meet at the Mid-Atlantic Ridge and close up on the ocean that now separates them." 1 |
The current theory, accepted by most geologists, is that the earth has an outer shell made up of six to eight large tectonic plates and many smaller ones. "Tectonic" comes from the Greek world "tekton" which means "builder." These relatively rigid masses of rock slide over the mantle. The mantle is composed of hot, soft rocks underneath the plates. Some geologists suggest that the mantle is in motion and carries the plates along with it.
About the South Asian tsunami:
Near Sumatra Island in Indonesia, there is a complex structure of tectonic plates involving the Burma plate, with the India and Australia plate to the west and the Sunda and Eurasian plates to the east. These plates are continually grinding against each other. They move very slowly -- only at about the rate, on average, that a human fingernail grows. Serious problems happen at subduction zones where one plate dives underneath the edge of an adjoining plate. Force builds up -- sometimes over hundreds of years -- until a rupture occurs and generates a violent earthquake. On 2004-DEC-26 -- the day after Christmas -- at 0758 local time (0058 GMT), an unusually powerful rupture occurred which generated a magnitude 9.15 earthquake "about [100 miles] 160 kilometers...off the coast of Indonesia's Sumatra Island at a depth of about [6.2 miles] 10 kilometers...." 3 It was the strongest earthquake anywhere on earth since the magnitude 9.2 quake which hit Prince William Sound, Alaska, in 1964. "The strongest quake on record hit Chile in 1960 and measured 9.5 on the Richter scale." 4 The energy in earthquakes increases by a factor of ten for each one point increase in the open-ended Richter scale. Thus a magnitude 9 earthquake contains a thousand times the energy of a magnitude 6 earthquake.
The earthquake was detected by sensors at earthquake observatories round the world. Quakes approaching 9 on the Richter scale are capable of generating a tsunami. This earthquake sent a sea surge in the Indian Ocean which probably reached speeds of 270 mph (450 km/hr) in open water. After about three hours, it approached Sri Lanka. It slowed down to perhaps 27 mph (45 km/hr) as it neared land, where it was squeezed upwards to produce a wave capable of massive destruction. 3
The first sign from land of a tsunami is that water is sucked away from the beach. In some areas, this tsunami exposed the ocean bottom near the shore, stranding fish. Many villagers rushed to collect the fish, were hit by the sea surge, and killed.
In early 2005-FEB, scientists at NASA said that the earthquake that caused the tsunami disrupted the Earth's rotation and shaved 2.68 microseconds from the length of each day. The North Pole shifted by about one inch. The planet is now slightly less oblate -- that is, not quite as flattened at the poles. 8
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Reducing the death toll from the next tsunami:
It is quite impossible to rearrange tectonic plates, prevent earthquakes, or prevent tsunamis. But there are ways to minimize some of the devastation and loss of life:
| Where possible, establishing a green belt of trees at the shore to adsorb some of the force of the sea surge. |
| Educating people who live near the ocean to be aware that the first sign of an oncoming tsunami may be a retraction of the water from the shore. If they see that happening again, they need to move inland as fast as possible. |
| Developing evacuation programs to evacuate to higher floors of strongly constructed buildings and/or a sufficient distance from the shore line. |
| Develop a warning system such as the one that currently exists in the countries bordering the Pacific Ocean. Such a system is being implemented worldwide. |
Benefits of the motion of the tectonic plates:
It is difficult to talk about the benefits of tectonic plates with the realization that their motion created a tsunami which recently snuffed out the lives of about 155,000 people. However, the same shifting of tectonic plates that causes earthquakes and generated the South Asia tsunami is also partly responsible for life on earth.
Dr. Donald J. DePaolo, a geochemist at the University of California, Berkeley, said:
"It's hard to find something uplifting about 150,000 lives being lost. But the type of geological process that caused the earthquake and the tsunami is an essential characteristic of the earth. As far as we know, it doesn't occur on any other planetary body and has something very directly to do with the fact that the earth is a habitable planet." 5
If tectonic plates existed elsewhere in the solar system's approximately 70 planets and moons, they would have produced mountain ranges of the type seen on Earth. None have been seen.
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