Category Science

Earthquakes are one of the most destructive forces on Earth. They happen quite frequently, though most of them are relatively minor. Powerful quakes, depending on where they happen, cause severe damage, toppling buildings and sometimes killing many thousands of people. They happen when tension created by the movement of the Earth’s tectonic plates is released, causing the rocks to shift and break suddenly. The incredible amount of force required to break the rocks is what makes earthquakes so devastating.

If your heart beats rapidly during an earthquake, it still doesn’t compete with high-frequency waves generated by the quake. These waves shake the ground faster than your ticker’s thrumming and cause the most damage to smaller structures, such as house­­s.

Researchers now have a new explanation for the source of these poorly understood high-frequency seismic waves. The longer a fault heals between earthquakes, the faster the waves once the fault finally breaks again, according to a new study detailed in the Oct. 31 issue of the journal Nature.

“We can think of a fault as just as crack or a cut in the ground. When they heal, it may not be all that different than how a cut in your skin heals. There are physical and chemical changes that occur right on the surface,” said Gregory McLaskey, lead study author and a postdoctoral researcher at the U.S. Geological Survey in Menlo Park, Calif.

Though the next quake may not be bigger in terms of magnitude, it could be much more intense, with more rapid shaking, he said.

“It doesn’t just affect the strength of it, it affects the way the ground will shake when it ruptures. The more the fault has healed, the more rapid vibrations and jolts will be produced when the earthquake does come,” McLaskey told OurAmazingPlanet.

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The whole of the Earth’s crust is subject to continental drift, including the ocean floor. Most of the tectonic plates are both continental (part of the land) and oceanic (part of the ocean floor). Evidence of movement on the sea bed is found in different magnetic alignments in the rock and volcanic activity on the ocean floor.

Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources. The structure of the oceans, starting with the continents, begins usually with a continental shelf, continues to the continental slope – which is a steep descent into the ocean, until reaching the abyssal plain – a topographic plain, the beginning of the seabed, and its main area. The border between the continental slope and the abyssal plain usually has a more gradual descent, and is called the continental rise, which is caused by sediment cascading down the continental slope.

The mid-ocean ridge, as its name implies, is a mountainous rise through the middle of all the oceans, between the continents. Typically a rift runs along the edge of this ridge. Along tectonic plate edges there are typically oceanic trenches – deep valleys, created by the mantle circulation movement from the mid-ocean mountain ridge to the oceanic trench.

Hotspot volcanic island ridges are created by volcanic activity, erupting periodically, as the tectonic plates pass over a hotspot. In areas with volcanic activity and in the oceanic trenches there are hydrothermal vents – releasing high pressure and extremely hot water and chemicals into the typically freezing water around it.

Deep ocean water is divided into layers or zones, each with typical features of salinity, pressure, temperature and marine life, according to their depth. Lying along the top of the abyssal plain is the abyssal zone, whose lower boundary lies at about 6,000 m (20,000 ft). The hadal zone – which includes the oceanic trenches, lies between 6,000–11,000 metres (20,000–36,000 ft) and is the deepest oceanic zone.

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Fossilized remains found in different parts of the world are good evidence that the continents were once joined together. Remains of the same animal have been found in both South America and Africa, which means it must have lived at a time when the continents were part of the same land mass. Plant fossils of the same type and age have been found all over the world, and geologists have identified parts of the same mountain range in different continents.

Alfred Wegener collected diverse pieces of evidence to support his theory, including geological “fit” and fossil evidence. It is important to know that the following specific fossil evidence was not brought up by Wegener to support his theory. Wegener himself did not collect the fossils but he called attention to the idea of using these scientific doc   uments stating there were fossils of species present in separate continents in order to support his claim.

Geological “fit” evidence is the matching of large-scale geological features on different continents. It has been noted that the coastlines of South America and West Africa seem to match up, however more particularly the terrains of separate continents conform as well. Examples include: the Appalachian Mountains of eastern North America linked with the Scottish Highlands, the familiar rock strata of the Karroo system of South Africa matched correctly with the Santa Catarina system in Brazil, and the Brazil and Ghana mountain ranges agreeing over the Atlantic Ocean.

Another important piece of evidence in the Continental Drift theory is the fossil relevance. There are various examples of fossils found on separate continents and in no other regions. This indicates that these continents had to be once joined together because the extensive oceans between these land masses act as a type of barrier for fossil transfer. Four fossil examples include: the Mesosaurus, Cynognathus, Lystrosaurus, and Glossopteris.

The Mesosaurus is known to have been a type of reptile, similar to the modern crocodile, which propelled itself through water with its long hind legs and limber tail. It lived during the early Permian period (286 to 258 million years ago) and its remains are found solely in South Africa and Eastern South America. Now if the continents were in still their present positions, there is no possibility that the Mesosaurus would have the capability to swim across such a large body of ocean as the Atlantic because it was a coastal animal.

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Continental drift is still happening, and the continents will continue to move in the future. They are unlikely to return to the shape of Pangaea, but a map of the world 150 million years from now could look significantly different from today’s.

Many times in Earth’s past the continents have been dispersed across the globe, kept apart by spreading oceans. But eventually oceans begin to close, and far-flung lands are drawn inexorably together. They fuse in crunching collisions, welding themselves into single vast terrains: supercontinents.

Continents are short-lived unions. Stirred by hot currents below, these great continental collages are destined to break up and once again go their separate ways. It’s the planet’s version of a family Christmas. Except rather than return every year, Earth’s Continent boom-and-bust cycles last 500 million years. Lost worlds litter our planet’s past – the ancestral supercontinents of Ur, Kenorland, Nuna, Rhodinia, and Pannotia.

Earth’s most recent grand union was 250 million years ago, when a continental mashup brought Pangea together. The giant landmass survived a mere 50 million years. It was undone by splits that tugged its American margins free from its African centre, broke apart the antipodean lands and then cleaved an Atlantic rift northward to release the conjoined bulk of Europe and Asia.

Neighbouring landmasses set off on different trajectories. India, originally snug with Madagascar, sped northwards to plough into Asia, thrusting ancient seafloor up into Himalayan peaks. The divorce of Australia and Antarctica left one to drift off into drier desert latitudes while the other languished in polar isolation. As these vast crustal rafts drifted across the globe, so landscapes and life adjusted. Each continent has been fashioned by that escape from Pangea.

But the continents are starting to come together again. North Africa is advancing into Mediterranean Europe, and over the next few tens of millions of years its shores will crumple into a chain of snowy peaks. Australia – the fastest-moving continent – is already beginning to sweep up New Guinea and the Indonesian archipelago en route to a messy pile-up with Asia. Pangea is slowly reassembling. Give the planet a couple of hundred millions years and we’ll have another supercontinent. Geologists even have a name for it: Pangea Ultima.

A glance at a modern map of the world makes it easy to see that all the continents were once joined together. Perhaps the clearest example is the east coast of South America and the west coast of Africa. Their shapes suggest that they would fit closely if brought together.

In the beginning, more than 4.6-billion years ago, the world was a ball of burning gas, spinning through space. At first, super-heated gases were able to escape into outer space, but as the Earth cooled, they were held by gravity to form the early atmosphere.

Clouds began to develop as water vapour collected in the air … And then it began to pour with rain, causing the early oceans to rise up.It took hundreds of millions of years for the first land masses to emerge.

About 250-million years ago, long, long after the Earth had formed, all the continents of the time had joined together to form a super-continent called Pangaea.

This super-continent broke up about 200-million years ago to form two giant continents, Gondwana and Laurasia. Gondwana comprised what is now Africa, South America, Australia, Antarctica and India. The Indian sub-continent lay off the east coast of Africa, before it broke off and moved north rapidly.

It collided with Asia, creating one of the world’s greatest mountain ranges, which extends for more than 2,500 kilometres – the Himalayas. By now, our world had started to look like something we would recognise.

The amazing process of plate tectonics, in which the Earth’s land masses move slowly across the Earth’s crust, is still continuing. Far in the future, some scientists have predicted that the present continents will converge again, to form a new supercontinent.

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There are a number of theories about the causes of continental drift. One puts forward the idea that hot rocks rise through ocean ridges, cool down and then drag the plates downwards. Another theory suggests that the heat from inside the Earth creates movement in the mantle. The resulting currents then shift the plates around. The third idea is the simplest. At the ocean ridges, the plates are higher than elsewhere, resulting in the force of gravity pulling the plates downwards.

The Earth is in a constant state of change. Earth’s crust, called the lithosphere, consists of 15 to 20 moving tectonic plates. The plates can be thought of like pieces of a cracked shell that rest on the hot, molten rock of Earth’s mantle and fit snugly against one another. The heat from radioactive processes within the planet’s interior causes the plates to move, sometimes toward and sometimes away from each other. This movement is called plate motion, or tectonic shift.

Our planet looks very different from the way it did 250 million years ago, when there was only one continent, called Pangaea, and one ocean, called Panthalassa. As Earth’s mantle heated and cooled over many millennia, the outer crust broke up and commenced the plate motion that continues today.

The huge continent eventually broke apart, creating new and ever-changing land masses and oceans. Have you ever noticed how the east coast of South America looks like it would fit neatly into the west coast of Africa? That’s because it did, millions of years before tectonic shift separated the two great continents.

Earth’s land masses move toward and away from each other at an average rate of about 0.6 inch a year. That’s about the rate that human toenails grow! Some regions, such as coastal California, move quite fast in geological terms — almost two inches a year — relative to the more stable interior of the continental United States. At the “seams” where tectonic plates come in contact, the crustal rocks may grind violently against each other, causing earthquakes and volcano eruptions. The relatively fast movement of the tectonic plates under California explains the frequent earthquakes that occur there.

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