Europe has no desert. Africa, the world's hottest landmass, has no cold climate. Australia has no active volcanoes. Australia has only one country, Australia. Which one of these is not a continent? Answer: France is not a continent. Is Australia a continent or island? Australia is the largest landmass on the continent of Australia.
Oceania is a region made up of thousands of islands throughout the Central and South Pacific Ocean. It includes Australia, the smallest continent in terms of total land area. Are there 5 or 7 continents in the world? All the continents of the world start and end with the same alphabet if you consider North and South Americas as one continent.
What are the 7 regions in the world? Generally identified by convention rather than any strict criteria, up to seven regions are commonly regarded as continents. What is the 8th continent? With this technology, Zealandia is clearly visible as a misshapen mass almost as large as Australia.
Satellite data can be used to visualise the continent of Zealandia, which appears as a pale blue upside-down triangle to the east of Australia Credit: GNS Science. When the continent was finally unveiled to the world, it unlocked one of the most sizeable maritime territories in the world. In addition to New Zealand, the continent encompasses the island of New Caledonia — a French colony famous for its dazzling lagoons — and the tiny Australian territories of Lord Howe Island and Ball's Pyramid.
The latter was described by one 18th-Century explorer as appearing " not to be larger than a boat. Zealandia was originally part of the ancient supercontinent of Gondwana, which was formed about million years ago and essentially lumped together all the land in the southern hemisphere. It occupied a corner on the eastern side, where it bordered several others, including half of West Antarctica and all of eastern Australia. Then around million years ago, "due to a process which we don't completely understand yet, Zealandia started to be pulled away", says Tulloch.
Continental crust is usually around 40km deep — significantly thicker than oceanic crust, which tends to be around 10km. As it was strained, Zealandia ended up being stretched so much that its crust now only extends 20km Eventually, the wafter-thin continent sank — though not quite to the level of normal oceanic crust — and disappeared under the sea. Despite being thin and submerged, geologists know that Zealandia is a continent because of the kinds of rocks found there. Continental crust tends to be made up of igneous, metamorphic and sedimentary rocks — like granite, schist and limestone, while the ocean floor is usually just made of igneous ones such as basalt.
When the supercontinent of Gondwana broke up, fragments drifted all across the globe. But there are still many unknowns. The unusual origins of the eighth continent make it particularly intriguing to geologists, and more than a little baffling. For example, it's still not clear how Zealandia managed to stay together when it's so thin and not disintegrate into tiny micro-continents.
Another mystery is exactly when Zealandia ended up underwater — and whether it has ever, in fact, consisted of dry land. The parts that are currently above sea level are ridges that formed as the Pacific and Australian tectonic plates crumpled together.
Tulloch says opinion is split as to whether it was always submerged apart from a few small islands, or once entirely dry land. With its mild climate and 39 million-sq-mile million-sq-km range, Gondwana itself was home to a vast array of flora and fauna, including the first four-limbed land animals and later, an abundance of the largest to ever live — the titanosaurs. So, could the rocks of Zealandia be studded with their preserved remains? Fossilised land animals are rare in the southern hemisphere, but the remains of several were found in New Zealand in the s, including the rib bone of a giant, long-tailed, long-necked dinosaur a sauropod , a beaky herbivorous dinosaur a hypsilophodont and an armoured dinosaur an ankylosaur.
Then in , the foot bone of a large carnivore , possibly a kind of allosaur, was discovered in the Chatham Islands, about miles km east of the South Island. Crucially, the fossils all date to after the continent of Zealandia split from Gondwana. The elephant bird stood 3 m 9. However, this doesn't necessarily mean there were dinosaurs roaming over the majority of Zealandia — these islands may have been sanctuaries while the rest was drowned, as it is now.
The plot thickens with one of New Zealand's weirdest and most beloved inhabitants, the kiwi — a dumpy, flightless bird with whiskers and hair-like feathers. Oddly, its closest relative is not thought to be the Moa, which is part of the same group — the ratites — and lived on the same island until its extinction years ago, but the even-more giant elephant bird, which stalked the forests of Madagascar until as recently as years ago.
The finding has led scientists to believe that both birds evolved from a common ancestor that lived on Gondwana. It took million years to fully break up , but when it did, it left behind fragments which have since been scattered all across the globe, forming South America, Africa, Madagascar, Antarctica, Australia, the Arabian Peninsula, the Indian Subcontinent, and Zealandia.
This, in turn, suggests that at least part of now-submerged Zealandia has remained above sea level the whole time. Except around 25 million years ago the entire continent — even possibly the entirety of New Zealand — is thought to have been plunged underwater. So what happened? Today, tectonic plates continue to slowly slide around the surface, just as they have been doing for hundreds of millions of years. Geologists believe the interaction of the plates, a process called plate tectonics , contributed to the creation of continents.
Studies of rocks found in ancient areas of North America have revealed that the oldest known pieces of the continents began to form nearly four billion years ago, soon after Earth itself formed. At that time, a primitive ocean covered Earth. Only a small fraction of the crust was made up of continental material.
Scientists theorize that this material built up along the boundaries of tectonic plates during a process called subduction. During subduction, plates collide, and the edge of one plate slides beneath the edge of another. Once melted, the rock became lighter. Called magma , it rose through the overlying plate and burst out as lava. When the lava cooled, it hardened into igneous rock. Gradually, the igneous rock built up into small volcanic islands above the surface of the ocean. Over time, these islands grew bigger, partly as the result of more lava flows and partly from the buildup of material scraped off descending plates.
When plates carrying islands subducted, the islands themselves did not descend into the mantle. Their material fused with that of islands on the neighboring plate. This made even larger landmasses—the first continents. The building of volcanic islands and continental material through plate tectonics is a process that continues today.
Continental crust is much lighter than oceanic crust. In subduction zones, where tectonic plates interact with each other, oceanic crust always subducts beneath continental crust. Oceanic crust is constantly being recycled in the mantle. For this reason, continental crust is much, much older than oceanic crust. Wandering Continents If you could visit Earth as it was millions of years ago, it would look very different. The continents have not always been where they are today. About million years ago, most continents were scattered chunks of land lying along or south of the Equator.
By about million years ago, the forces that helped form Pangaea caused the supercontinent to begin to break apart. The pieces of Pangaea that began to move apart were the beginnings of the continents that we know today. A giant landmass that would become Europe, Asia, and North America separated from another mass that would split up into other continents.
In time, Antarctica and Australia, still joined together, broke away and drifted south. The small piece of land that would become the peninsula of India broke away and for millions of years moved north as a large island. It eventually collided with Asia. Gradually, the different landmasses moved to their present locations. The positions of the continents are always changing.
North America and Europe are moving away from each other at the rate of about 2. If you could visit the planet in the future, you might find that part of the United States's state of California had separated from North America and become an island.
Africa might have split in two along the Great Rift Valley. It is even possible that another supercontinent may form someday. Continental Features The surface of the continents has changed many times because of mountain building, weathering , erosion , and build-up of sediment. Continuous, slow movement of tectonic plates also changes surface features. The rocks that form the continents have been shaped and reshaped many times. Great mountain ranges have risen and then have been worn away.
Ocean waters have flooded huge areas and then gradually dried up. Massive ice sheets have come and gone, sculpting the landscape in the process. Today, all continents have great mountain ranges, vast plains, extensive plateaus, and complex river systems.
Although each is unique , all the continents share two basic features: old, geologically stable regions, and younger, somewhat more active regions. In the younger regions, the process of mountain building has happened recently and often continues to happen. The power for mountain building, or orogeny , comes from plate tectonics. One way mountains form is through the collision of two tectonic plates. The impact creates wrinkles in the crust, just as a rug wrinkles when you push against one end of it.
The plate carrying India slowly and forcefully shoved the landmass of India into Asia, which was riding on another plate. The collision continues today, causing the Himalayas to grow taller every year. Recently formed mountains, called coastal ranges, rise near the western coasts of North America and South America. Older, more stable mountain ranges are found in the interior of continents. The Appalachians of North America and the Urals, on the border between Europe and Asia, are older mountain ranges that are not geologically active.
Even older than these ancient, eroded mountain ranges are flatter, more stable areas of the continents called cratons. Every continent has a craton. Microcontinents, like New Zealand, lack cratons.
Cratons have two forms: shields and platforms. Shields are bare rocks that may be the roots or cores of ancient mountain ranges that have completely eroded away.
Platforms are cratons with sediment and sedimentary rock lying on top. The Canadian Shield makes up about a quarter of North America. For hundreds of thousands of years, sheets of ice up to 3.
The moving ice wore away material on top of ancient rock layers, exposing some of the oldest formations on Earth. When you stand on the oldest part of the Canadian Shield, you stand directly on rocks that formed more than 3. North America North America, the third-largest continent, extends from the tiny Aleutian Islands in the northwest to the Isthmus of Panama in the south.
The continent includes the enormous island of Greenland in the northeast. In the far north, the continent stretches halfway around the world, from Greenland to the Aleutians. In between the mountain systems lie wide plains that contain deep, rich soil. Much of the soil was formed from material deposited during the most recent glacial period. This Ice Age reached its peak about 18, years ago.
As glaciers retreated, streams of melted ice dropped sediment on the land, building layers of fertile soil in the plains region. North America contains a variety of natural wonders. Landforms and all types of vegetation can be found within its boundaries. Yellowstone National Park, in the U. Despite its name, Greenland is mostly covered with ice. Its ice is a remnant of the great ice sheets that once blanketed much of the North American continent.
Greenland is the only place besides Antarctica that still has an ice sheet. From the freezing Arctic to the tropical jungles of Central America , North America enjoys more climate variation than any other continent. Parts of the Canadian province of British Columbia and the U. South America is the fourth-largest continent and extends from the sunny beaches of the Caribbean Sea to the frigid waters near the Antarctic Circle.
These islands even host some Antarctic birds, such as penguins, albatrosses, and terns. Early Spanish explorers visiting the islands for the first time saw small fires dotting the land. These fires, made by indigenous people, seemed to float on the water, which is probably how the islands got their name—Tierra del Fuego means "Land of Fire. Many active volcanoes dot the range. These volcanic areas are fueled by heat generated as a large oceanic plate, called the Nazca Plate, grinds beneath the plate carrying South America.
The central-southern area of South America has pampas , or plains. These rich areas are ideal for agriculture. The growing of wheat is a major industry in the pampas. Grazing animals, such as cattle and sheep, are also raised in the pampas region. In volume, the Amazon is the largest river in the world. More water flows from it than from the next six largest rivers combined. Water flows more than meters 3, feet —almost a mile.
The falls are so high that most of the water evaporates into mist or is blown away by wind before it reaches the ground.
0コメント