Why are kangaroos only found in Australia? Detailed answer

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Why are kangaroos only found in Australia? Detailed answer

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Why are kangaroos only found in Australia?

Even 200 years ago, no one knew about the existence of kangaroos, except for the natives. They were first seen by explorers and settlers in Australia. Kangaroos certainly have a pouch, and in Australia many mammals have pouches. Australia and the islands adjacent to it are the place where most of the marsupials live. Marsupials are one of the orders of mammals.

The first mammals appeared over 100 million years ago, during the time of the dinosaurs. Some were marsupials and some were placental. Placental mammals provided food for unborn babies in the mother's body. In marsupials, a bag served for this purpose. The cubs were born very small and developed in the mother's pouch.

When the climate changed on Earth, the dinosaurs became extinct. Mammals multiplied and developed extremely. They have become the main animals on Earth. It turned out that placental animals are more adapted to new conditions than marsupials. They have a better developed brain, and the cubs develop much better inside the mother's body than in the bag.

In almost all parts of the world marsupials have disappeared. They could not compete for living space with other mammals. But this did not happen in Australia and South America. Scientists believe that once Australia was connected to Southeast Asia by a chain of islands or an isthmus, and marsupials spread across Australia at a time when highly developed placental mammals had not yet appeared there. They had no rivals, and therefore they felt great and developed.

Author: Likum A.

Random interesting fact from the Great Encyclopedia:

What is uranium?

Uranium has existed on earth for billions of years, but most people did not know about it until after the creation of nuclear weapons and nuclear power plants. Uranium is one of the heaviest chemical elements. It is a metal and its content in the earth's crust is higher than such well-known elements as mercury and silver.

Deposits of uranium ores have been discovered in many regions of the globe. Their deposits are especially large in Russia, Canada, the USA, Zaire and some other countries. Pure metallic uranium glistens just like silver. However, if you hold it for several minutes in air, the surface of a piece of metal tarnishes and acquires a brown tint. A film of uranium oxide is formed on it - a compound of uranium with oxygen, and the process of its formation is called oxidation. The film, formed on the metal surface, prevents the penetration of oxygen into the sample and further development of the oxidation process.

The main difference between uranium and the vast majority of other elements is that it has natural radioactivity. This means that the uranium atoms themselves are gradually changing, while emitting certain types of rays invisible to the eye. These rays are of three types, called alpha, beta and gamma radiation. In the process of changes undergone by uranium atoms, they turn into another radioactive element. The same thing happens with the new element, and a new portion of radiation is released. This continues until a new element is formed that is not radioactive. There are 14 stages in this chain of transformations. On one of them, the well-known element radium is formed, and on the last, lead.

Lead is a non-radioactive element, and therefore the chain of transformations ends on it. The complete process of converting uranium to lead takes billions of years. Uranium has several isotopes. Isotopes are atoms of the same element that have different atomic weights, which are indicated by numbers after the name of the element.

Uranium-235 is used as a material for atomic bombs and fuel for nuclear power plants. Another element - plutonium, used for the same purposes - does not exist in nature, and it is obtained from uranium using special devices.

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