It is believed that the earth was formed nearly 4.6 billion years ago from nebula, a cloud of dust particles and gas. Sun stars and all other planets are formed in a same way. So millions of years ago a hot glowing ball was formed having millions of degree Fahrenheit temperature. Because of this all the gases and particles came together and was compressed, this process gave off a lot of heat. Now the gases start changing to the liquid state. This liquid material came in the middle of earth and settled there as it was heavier than the gases and upper part formed the solid crust. The internal molten center was still very hot because at that time our planet was having no ozone layer and no oxygen. So the ultra violet rays directly strike the earth causing the inner matter to remain liquid.
Many volcanoes erupted, which resulted in the formation of mountains, hills. And water droplets was able to change in liquid because of the high temperature of earth. Now after million years the temperature somewhat lowered and the water vapors start condensing and settled in the oceans. Volcanic eruptions also gradually decreased. Green algae started forming in the water which released oxygen in the air and finally ozone layer was also formed.
After many million years life started on earth in form of trees which has reduced the temperature and now earth has started experiencing changeable weather. During this period dinosaurs existed on the earth. After another thousands of years later it is said that big meteorite stroked the earth and dinosaurs died because of suffocation created by the dust particles caused due to collision. After this all settled and life again started and human beings came into existence.
Earth is still developing and its internal part is still in molten state which causes volcanoes and plates present on the earth’s surface is also colliding with each other which sometimes cause earthquake. Nobody knows in future what will happen. Some species are dying as the conditions are not suitable for them and some new will come to existence.
So we can say that since its formation the earth is in a continuous process of development.