The Road to Life
Scientists generally think the Earth came into istenc 4.6 billion years ago. If you could have seen it back then, you wouldn't have recognize it wouldnt 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 volcanoes laya today. This cooling magma released water vapor! creating the oceans. However, there was n oxygen and the air couldn't support life.
A The first land plants were similar t Then, about 3.5 billion years ago single-celled blue this whisk fern, in Hawaii, USA. cyanobacteria started to exist. onginally, 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 by little, th 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 20 in the atmosphere had risenenough for other things to live.
Scientists believe the very first land plants appea and produced oxygen, around 470 million years 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.
25 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- jst s they have for billions of years.