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How did Earth form?

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. 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 occasionally 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 Billion 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 Billion 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 Million 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 Million Years Ago

Life was wiped off the face of the planet! It is believed that a huge meteorite or comet 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.

TOP TEN FACTS ABOUT EARTH

Fact One

Earth is the only planet in the Solar System to have water in its three states of matter: as a solid (ice), a liquid (sea, rain, etc.) and as a gas (clouds). These are all shown below. Water is, of course, the most important liquid for life.

Fact Two

Earth is almost five billion years old, although life (resembling life as we know it) has only existed on the planet for the last 150 million to 200 million years. This means that life has only been present on Earth for only 5%-10% of its lifetime.

Fact Three

Earth and Mercury are the two most dense planets in the Solar System. This means that particles inside the planet are most closely packed together.

Fact Four

The length of time it takes for Earth to orbit the Sun is 365 and a quarter days. To make up this extra quarter which isn't counted at the end of a year, we have an extra day every four years on 29th February. The next Leap Year will be in 2012.

Fact Five

Earth is gradually slowing down. Every few years, an extra second is added to make up for lost time. Millions of years ago, a day on Earth will have been 20 hours long. It is believed that, in millions of years time, a day on Earth will be 27 hours long.

Fact Six

The centre of the Earth, its core, is molten. This means that it is liquid rock which sometimes erupts onto the surface through volcanic eruptions. This core is 7,500°c, hotter than the surface of the Sun!

Fact Seven

Earth is the only planet in the Solar System not to be named after a mythical God.

Fact Eight

Despite being called Earth, only 29% of the surface is actually 'earth.' The rest of the planet's surface (71%) is made up of water.

Fact Nine

From a distance, Earth would be the brightest of the planets. This is because sunlight is reflected off the planet's water.

Fact Ten

Earth is the only planet in the Solar System known to be geologically active, with Earthquakes and volcanoes forming the landscape, replenishing carbon dioxide into the atmosphere and erasing impact craters from meteors.