Category Geography

FROM WHERE IN THE SUPERCONTINENT DID ANTARCTICA BREAK AWAY?

Gondwana was an ancient supercontinent that broke up about 180 million years ago. The continent eventually split into landmasses we recognize today: Africa, South America, Australia, Antarctica, the Indian subcontinent and the Arabian Peninsula.

According to plate tectonic evidence, Gondwana was assembled by continental collisions in the Late Precambrian (about 1 billion to 542 million years ago). Gondwana then collided with North America, Europe, and Siberia to form the supercontinent of Pangea. The breakup of Gondwana occurred in stages. Some 180 million years ago, in the Jurassic Period, the western half of Gondwana (Africa and South America) separated from the eastern half (Madagascar, India, Australia, and Antarctica). The South Atlantic Ocean opened about 140 million years ago as Africa separated from South America. At about the same time, India, which was still attached to Madagascar, separated from Antarctica and Australia, opening the central Indian Ocean. During the Late Cretaceous Period, India broke away from Madagascar, and Australia slowly rifted away from Antarctica. India eventually collided with Eurasia some 50 million years ago, forming the Himalayan Mountains, while the northward-moving Australian plate had just begun its collision along the southern margin of Southeast Asia.

Credit: Britannica

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WHAT IS CONTINENTAL DRIFT?

In the early 20th century, German scientist Alfred Wegener termed the movement over geological time of Earth’s major landmasses- Europe, the Americas, Africa, Australia, Asia and Antarctica- as ‘continental drift’. However, the modern day term is plate tectonics. Wegener suggested that landmasses may have pulled apart or pushed together to create new landforms. For example, he found evidence for this when he discovered fossils in Norway that indicated they originated in a tropical climate.

Continental drift describes one of the earliest ways geologists thought continents moved over time. Today, the theory of continental drift has been replaced by the science of plate tectonics.

The theory of continental drift is most associated with the scientist Alfred Wegener. In the early 20th century, Wegener published a paper explaining his theory that the continental landmasses were “drifting” across the Earth, sometimes plowing through oceans and into each other. He called this movement continental drift. 

Pangaea

Wegener was convinced that all of Earth’s continents were once part of an enormous, single landmass called Pangaea.

Wegener, trained as an astronomer, used biology, botany, and geology describe Pangaea and continental drift. For example, fossils of the ancient reptile mesosaurus are only found in southern Africa and South America. Mesosaurus, a freshwater reptile only one meter (3.3 feet) long, could not have swum the Atlantic Ocean. The presence of mesosaurus suggests a single habitat with many lakes and rivers.

Wegener also studied plant fossils from the frigid Arctic archipelago of Svalbard, Norway. These plants were not the hardy specimens adapted to survive in the Arctic climate. These fossils were of tropical plants, which are adapted to a much warmer, more humid environment. The presence of these fossils suggests Svalbard once had a tropical climate.

Finally, Wegener studied the stratigraphy of different rocks and mountain ranges. The east coast of South America and the west coast of Africa seem to fit together like pieces of a jigsaw puzzle, and Wegener discovered their rock layers “fit” just as clearly. South America and Africa were not the only continents with similar geology. Wegener discovered that the Appalachian Mountains of the eastern United States, for instance, were geologically related to the Caledonian Mountains of Scotland.

Pangaea existed about 240 million years ago. By about 200 million years ago, this supercontinent began breaking up. Over millions of years, Pangaea separated into pieces that moved away from one another. These pieces slowly assumed their positions as the continent we recognize today.

Credit: National Geographic Society

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WHY DO CREATURES GO EXTINCT?

Extinction is when an entire population of a particular creature disappears from Earth. Though it sounds drastic, extinctions are quite common in Earth’s history. Scientists believe that 99 per cent – over five billion species that ever lived – have become extinct since the beginning of life. This could have happened due to reasons of lack of food or disastrous events like asteroids hitting Earth. In recent times, the speed at which species are becoming extinct has increased due to human activity.

The most common cause of extinction is a sudden, serious change in a species’ habitat. A habitat is the surroundings in which an animal lives. Animals can rarely survive such sudden change. Their food supply may be wiped out. They may also lose shelter or other things that they need to survive.

Many things can change a species’ habitat. Floods, fires, droughts, volcanoes, and other natural events may be causes. People also change the environment in ways that drastically affect animals. People clear forests and drain wetlands. They build dams that disrupt the flow of rivers. They build cities on land that animals need to survive. They also create harmful pollution.

Some changes that cause extinction affect only a small area. Others are large enough to affect the entire world. A fire or other local event may cause the extinction of animals that live only in that region. A sudden change in the global climate might wipe out an animal species that lives in many parts of the world.

People can cause extinctions more directly as well. Some species have been hunted to extinction. The passenger pigeon is one example of this. Humans killed millions of the birds over many years. The last one died in the early 1900s.

Dinosaurs first appeared on Earth about 215 million years ago. They were the most important land animals for more than 150 million years. By 65 million years ago, however, the dinosaurs had died out.

Many scientists believe that a large asteroid, or rock from space, caused this mass extinction. When the asteroid hit Earth, the impact caused drastic changes. Thick dust and other materials blocked the sun. Temperatures dropped, and plants could not grow. The dinosaurs could not survive the cold temperatures and lack of food. But early species of birds and mammals did survive.

Credit: Kids Britannica

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WHAT IS EVOLUTION?

Life has existed on Earth for millions of years. Living forms and creatures have inhabited almost all of Earth and over the years have changed and transformed from the way they existed many years ago. This transformation and modification in features and functions in living beings is called evolution – though it is believed that a few creatures, like the modern cockroach and the crocodile, have not changed since the era of dinosaurs.

Evolution is a process that results in changes in the genetic material of a population over time. Evolution reflects the adaptations of organisms to their changing environments and can result in altered genes, novel traits, and new species. Evolutionary processes depend on both changes in genetic variability and changes in allele frequencies over time.

The study of evolution can be performed on different scales. Microevolution reflects changes in DNA sequences and allele frequencies within a species over time. These changes may be due to mutations, which can introduce new alleles into a population. In addition, new alleles can be introduced in a population by gene flow, which occurs during breeding between two populations that carry unique alleles. In contrast with microevolution, macroevolution reflects large-scale changes at the species level, which result from the accumulation of numerous small changes on the micro-evolutionary scale. An example of macroevolution is the evolution of a new species.

One mechanism that drives evolution is natural selection, which is a process that increases the frequency of advantageous alleles in a population. Natural selection results in organisms that are more likely to survive and reproduce. Another driving force behind evolution is genetic drift, which describes random fluctuations in allele frequencies in a population. Eventually, genetic drift can cause a subpopulation to become genetically distinct from its original population. Indeed, over a long period of time, genetic drift and the accumulation of other genetic changes can result in speciation, which is the evolution of a new species.

Credit: Scitable by nature education

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HOW ARE FOSSILS FORMED?

When a plant or animal is buried quickly, it gets enclosed in sediment before it decomposes. As pressure transforms this sediment into rock, a hollow mould of the organism is formed. Gradually minerals seep into this hollow and harden over time to form a detailed, three-dimensional cast. Soft tissue organisms are preserved as impressions between layers of sediment. Perfectly preserved fossils of insects and other small forms of life have also been found trapped inside hardened tree sap.

The most common way an animal such as a dinosaur fossilises is called petrification. These are the key steps:

1. The animal dies.

2. Soft parts of the animal’s body, including skin and muscles, start to rot away. Scavengers may come and eat some of the remains.

3. Before the body disappears completely, it is buried by sediment – usually mud, sand or silt. Often at this point only the bones and teeth remain.

4. Many more layers of sediment build up on top. This puts a lot of weight and pressure onto the layers below, squashing them. Eventually, they turn into sedimentary rock.

5. While this is happening, water seeps into the bones and teeth, turning them to stone as it leave behind minerals.

This process can take thousands or even millions of years.

Credit: Natural History Museum

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WHY IS THE STUDY OF FOSSILS USEFUL?

Fossils, both plant and animal, are a valuable source of information on how life has evolved on Earth – they are a window into the past. They also provide insight on ecological, climatic and environmental changes that have taken place over the ages.

1. Beginnings of life. Apart from the sheer wonder they see the morphology of giant creatures millions of years ago from studying their fossil remains, fossils teach us about the beginnings and transformations of life itself.

2. Ecosystems. Fossils help us understand the environment where extinct life forms once existed.

3. Human origin. Paleo-anthropologists study the beginnings of human life, from the tools our ancestors used, the food they ate, their physical adjustments, to their social behaviour and migration.

4. Age of the country. All living organisms inhabited the Earth only at certain intervals and are reflected in the fossil record in sequence by each layer of rocky sediment.

5. Our past and future. The study of fossils also leads to discoveries and understandings of processes on Earth that may be of benefit to mankind.

It is wonderful for everyone to find stones that sometimes have figures of animals inside and out. People learn from fossils – Whether fossils are from humans or dinosaurs, they may not learn much about the species and cultures that existed in the past. Fossils give us educated guesses about the evolution of different species and what the climate looked like in the past.

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