HOW WAS EARTH FORMED?
Planet Earth was formed 4.6 billion years ago from the same nebula cloud of gas and dust that the Sun and the other planets were formed (similar to the one pictured to the left). However, Earth then was very different from Earth now, and it would have been impossible for life to exist on it. In fact, it is only quite recently in the Earth's 4,600,000,000 year long life that life, resembling modern-day life, has been possible, first with the dinosaurs over 200,000,000 years ago and now with humans and other animals. The Earth is still being formed now. It still has a molten centre which causes volcanoes to ocassionally erupt, and plates on the surface are constantly "swimming" meaning that they collide with other plates and cause earthquakes. On this page, we will look at how Earth may have settled to become like the planet it is now.
4,000,000,000 YEARS AGO
This is an artist's impression of what Earth looked like 4 billion years ago. The planet has no oxygen in its atmosphere and no ozone layer, so poisonous ultraviolet rays from the Sun hit the surface directly. The molten centre of the planet is still extremely hot, and volcanoes erupt constantly, forming the mountains and landscapes of the planet. Water droplets, contained in the planet's atmosphere, cannot settle as liquid or ice because the surface is so hot.
1,000,000,000 YEARS AGO
The planet has cooled and volcanic eruptions are less common. Water is now allowed to settle, and forms oceans. Green algae forms in the water, which photosynthesises and produces oxygen which is put into the air. The oxygen forms a layer of ozone which protects the Earth from poisonous ultraviolet rays from the Sun. Land drifts apart to begin forming continents.
400,000,000 YEARS AGO
Life begins developing in the form of trees and plants. These produce more oxygen. Earth has a cooler temperature, with changeable weather. This weather (rain, snow, wind, frost) causes the tops of the ancient volcanoes to wear away, creating lower ground. Dinosaurs eventually develop, ruling the planet. Flowers are later formed, along with insects.
65,000,000 YEARS AGO
Life was wiped off the face of the planet! It is believed that a huge meteorite hit the Earth's surface, causing clouds of dust which suffocated the dinosaurs and other creatures on the planet. Conditions on the planet were suffocating as poisonous chemicals were unable to leave the planet's atmosphere, and life-giving energy from the Sun could not enter. After settling again, the Earth was suitable for life, an the ancestors of human beings developed.
TODAY
Earth is still developing. Volcanoes still erupt, the earth still shakes, weather still forms landscapes. Creatures evolve. Some die out, some develop. The creatures that die out do so because they are not suitable for the planet's current conditions. Creatures that survive and flourish do so because they are more adapted to the new conditions. Nobody knows what the future holds. The air is becoming more polluted, and the temperature on the planet is gradually increasing. Earth's protective ozone is wearing away. Earth remains a target for meteors, comets and asteroids travelling through space. There is always a chance that one may hit the planet eventually and destroy life as we know it. Perhaps, the planet will be reborn again as the dust settles.
Selasa, 25 Agustus 2009
tugas explanation acep luki XI IPA 5
Nama : Acep Luki Lukman Hakim
Kelas : XI IPA 5
Absen : 31
How the Earth Formed
The earth was formed in the same way as the sun, planets, stars. At first the earth was a hot glowing ball of white hot gases with a temperature that was millions of degrees Fahrenheit. This was caused by particles of gases being drawn together and compressed, giving off a lot of heat. This happened millions of years ago.
Finally the earth cooled down. The ball of gas slowed down from spinning and the color changed from white to yellow to red to not giving off any light at all.
The earth contracted, getting smaller and the gases changed to liquid as they cooled. Heavier materials drew to the center of the earth. The heavier liquid settled at the middle of the earth. As the earth cooled more, a solid crust formed over the over the liquid material. As the crust cooled, it got wrinkled and burst open in spots. Gradually cracks formed in the crust. Water that formed under the earth's crust escaped from the cracks in the earth and soon water vapor formed above the earth. This lead to cloud formation. Larger droplets formed in the clouds and as they were pulled to the earth by gravity came the first rainfalls. The rain at first evaporated as soon as it hit the earth. Later, as the earth continued to cool, the rain stayed on to form lakes and oceans. At first the water was all fresh water, but as it had chemicals from the earth's crust mix in, the water of the oceans became salty. At one time the earth was all water on its surface.
Later pressure and heat in its center pushed up solid portions of the earth that became land forms. Sometimes the land would sink back down and other portions arise.
About three million years ago, the earth cooled a great deal and great sheets of ice called glaciers covered its surface. As the ice spread over the land, it gouged great valleys, rivers and lakes into the earth. About 8000 years ago the last glaciers melted, with the earth more as it is today.
Kelas : XI IPA 5
Absen : 31
How the Earth Formed
The earth was formed in the same way as the sun, planets, stars. At first the earth was a hot glowing ball of white hot gases with a temperature that was millions of degrees Fahrenheit. This was caused by particles of gases being drawn together and compressed, giving off a lot of heat. This happened millions of years ago.
Finally the earth cooled down. The ball of gas slowed down from spinning and the color changed from white to yellow to red to not giving off any light at all.
The earth contracted, getting smaller and the gases changed to liquid as they cooled. Heavier materials drew to the center of the earth. The heavier liquid settled at the middle of the earth. As the earth cooled more, a solid crust formed over the over the liquid material. As the crust cooled, it got wrinkled and burst open in spots. Gradually cracks formed in the crust. Water that formed under the earth's crust escaped from the cracks in the earth and soon water vapor formed above the earth. This lead to cloud formation. Larger droplets formed in the clouds and as they were pulled to the earth by gravity came the first rainfalls. The rain at first evaporated as soon as it hit the earth. Later, as the earth continued to cool, the rain stayed on to form lakes and oceans. At first the water was all fresh water, but as it had chemicals from the earth's crust mix in, the water of the oceans became salty. At one time the earth was all water on its surface.
Later pressure and heat in its center pushed up solid portions of the earth that became land forms. Sometimes the land would sink back down and other portions arise.
About three million years ago, the earth cooled a great deal and great sheets of ice called glaciers covered its surface. As the ice spread over the land, it gouged great valleys, rivers and lakes into the earth. About 8000 years ago the last glaciers melted, with the earth more as it is today.
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