Scientists generally think the Earth came into existence 4.6 billion years ago. If you could have seen it back then, you wouldn't have recognized it; it wouldn't have looked anything like the Earth we know now .So what did it look like And how did the Earth start to support life?
For the first 700 million years, huge pieces of solid rock floated in a sea of magma-the same magma that comes out of volcanoes as lave today. This cooling magma released water vapor, creating the oceans. However, there was no oxygen, and the air couldn't support life.
Then, about 3.5 billion years ago, single-celled blue-green cyanobacteria started to exist.Originally,they survived on chemicals within the water.However,slowly they changed. Over time, they developed the ability to turn energy from the sun into food.Little,the cyanobacteria helped turn the atmosphere into breathable air.
Stromatolites were also living on Earth 3.5 billion years ago. Part rock and part living things, they also helped create Earth's breathable air.By about 2.4 billion years ago, the level of oxygen in the atmosphere had risen enough for other things to live.
Scientists believe the very first land plants appeared, and produced oxygen, around 470 million year’s ago-millions of years before the first reptiles and mammals. At first, the plants were small and grew slowly. Over time, however, the plants developed stronger stems. Little by little, they grew taller and bigger.
Earth has seen an amazing series of changes. We can still see these processes today. For example, volcanoes still erupt, creating new land, and plants continue to make oxygen-juts as they have for billions of years