According to data for 2022, science knows about the existence of 2.16 million animal species. The most diverse in the world are insects, followed by mollusks, and only then vertebrates. Our planet is still poorly studied, so scientists predict that humanity has several million more previously unknown living creatures to discover. All living creatures are distributed in various corners of the globe: many animals live in tropical forests, some prefer deserts, and some have managed to get used to life in the cold corners of the planet. It is unlikely that many people thought about this, but here is an interesting question: how did animals appear on different continents and islands? Why do kangaroos live in Australia, and penguins in the Southern Hemisphere?
Little is said about the history of the spread of animals on Earth, although this is an extremely interesting topic. Source: tury.ru
Contents
- 1 How life developed on Earth
- 2 How the Earth changed millions of years ago
- 3 How animals evolved
- 4 Distribution of animals on Earth
How life developed on Earth
Life on Earth appeared approximately 4.1 billion years ago. The very first ancestor of all life on our planet was a microscopic organism, which is known by the acronym LUCA (Last Universal Common Ancestor). It consisted of only one cell, and without it, neither animals nor humans would exist on Earth today.
This is what the common ancestor of all living organisms LUCA looked like. Source: involta.media
At first, life existed only in water, in the form of various microbes. Over time, single-celled organisms turned into multicellular ones, they became larger. Then some species developed to such an extent that they came out of the water and began to live on land. In order to survive in different conditions, they changed their appearance, grew skin or fur, acquired sharp teeth for hunting other animals or long necks for eating leaves of tall trees.
How the Earth changed millions of years ago
Over billions of years, the face of our planet has been constantly changing. Today, the land is divided into continents like Eurasia, Africa, North and South America, and so on. But it wasn't always like that — for example, between 335 and 175 million years ago, the land was a supercontinent called Pangea. All the animals that existed in ancient times lived on this huge patch of land.
Supercontinent Pangea. Source: kosmokid.ru
Over time, due to the movement of tectonic plates, the supercontinent Pangea began to disintegrate into separate parts. These processes occurred slowly, over millions of years, and were accompanied by the formation of new oceans and seas. As a result of the disintegration, Pangea split into Laurasia and Gondwana, and then into modern continents. Along with the spread of continents, the ancestors of modern animals migrated and adapted to new conditions in different parts of the planet.
Read also: Why giant insects lived on Earth 300 million years ago
How animals evolved
Over the next millions of years, the ancestors of modern animals, who found themselves on different continents, gradually adapted to the new conditions. From them came modern living creatures, which are the native inhabitants of Australia, Antarctica and other parts of the world.
An example is how kangaroos became uniquely Australian. Marsupials, which include kangaroos, originated in what is now South America about 70-80 million years ago. At that time, the territories of South America, Antarctica, and Australia were connected to form the supercontinent Gondwana.
When Gondwana began to break apart, marsupials migrated from South America through Antarctica to the patch of land that is now Australia. The animals were able to cross Antarctica because millions of years ago it was much warmer there than it is today.
It can be said that the homeland of the kangaroo is South America. Source: drive2.ru
Approximately 40 million years ago, Australia separated from Antarctica so strongly that it turned into an independent, completely isolated continent. Its own climate was formed there, in which marsupials began to evolve independently of other groups of mammals.
The same thing happened with other animals. For example, modern penguins live in the Southern Hemisphere because millions of years ago their ancestors from the order of penguins (Sphenisciformes) ended up there. In the new place, the descendants of the ancient penguins adapted to the cold conditions. They developed a thick layer of fat to protect them from the cold and flippers for swimming after fish and other sea creatures.
This is amazing: Why do penguins fall into a 4-second sleep 10,000 times a day?
The distribution of animals on Earth
Of course, geographical changes are not the only reason why different animals live in different parts of the planet. Some birds have flown to other continents on their own, and fish are often transported to other places during storms. Many species of animals were brought to foreign continents by people. For example, there have never been cats in Australia before – people brought them, and the local nature was not ready for this. Today, cats pose a great threat to many Australian animals, so they are exterminated, and pets are prohibited from being allowed outside.
Cats pose a great threat to the nature of Australia. Source: herpeto-volga.ru
Some islands are home to unique animals that are not found in any other part of the world. For example, giant tortoises live on the Galapagos Islands. And the island of Madagascar has become home to lemurs and other tropical creatures. They are not found in other places because they are accustomed to the surrounding conditions, and they have no ways to migrate to other islands and continents.
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Mosquitoes, ants and other insects are found almost everywhere. This is due to the fact that for hundreds of years they were accidentally spread by people on ships and other means of transportation. And they are very tenacious creatures, capable of getting used to even the most unusual conditions for themselves.