Planet Earth was formed 4.6 billion years back from the identical nebula cloud of gas and dust that the Sun as well as the other planets had been formed. However, Earth then was very various from Earth now and it would have been difficult for life to exist on it.
Actually, it is only quite lately in the Earth's 4,600,000,000 year long life that life, like modern-day life, has been possible, initial with the dinosaurs over 200,000,000 years back and now with humans and other animals. The Earth is still getting formed now. It still has a molten centre that causes volcanoes to sometimes erupt and plates on the surface are continually swimming, which means that they collide with other plates and result in earthquakes.
The planet provides no oxygen in its atmosphere with no ozone layer, therefore poisonous uv rays from the Sun strike the surface straight. The molten centre of the planet is still very hot and volcanoes erupt continually, forming the mountains and landscapes of the planet. Water droplets, contained in the planet's atmosphere, cannot settle as liquid or ice since the surface is really hot.
The planet has cooled and volcanic eruptions are less common. Water is now permitted to settle and forms oceans. Green algae forms inside the water, which photosynthesises and creates oxygen that is put into the air. The oxygen forms a layer of ozone that protects the Earth from dangerous ultraviolet rays from the Sun. Land drifts apart to start forming continents.
Life starts developing in the type of trees and plants. These generate more oxygen. Earth features a cooler temperature, with adjustable weather. This weather (rain, snow, wind, frost) leads to the tops of the ancient volcanoes to wear away, producing lower ground. Dinosaurs eventually develop, ruling the planet. Flowers are afterwards formed, along with insects.
Life was wiped off the face of the planet. It is considered that a huge meteorite or comet strike the Earth's surface, causing clouds of dust that suffocated the dinosaurs and other animals on the planet. Circumstances on the planet were suffocating as dangerous chemicals were unable to leave the planet's atmosphere, and life-giving energy through the Sun could not get into. After settling again, the Earth was ideal for life and the ancestors of humans developed.
Earth is still developing. Volcanoes still erupt, the earth still shakes, weather still forms landscapes. Creatures develop. Some go extinct, others adjust to the changing planet. No one knows what the future holds. The air is getting more polluted and the temperature on the planet is gradually increasing. Earth stays a target for meteors, comets and asteroids travelling via space. There is always an opportunity that one may strike the planet eventually and ruin life as we know it. Perhaps, the planet will be reborn again as the dust settles