Compare the chemical composition of the Earth’s atmosphere before bacteria and plants evolved and after they became widespread.
Earth and Space Science
In prior grades students learned about a few of the methods that have made it possible to uncover the history of our planet. In grades 9-11 students learn about the major changes in Earth systems over geologic time and some of the methods used to gather evidence of those changes. Methods include observation and measurement of sediment layers, using cores drilled from the sea bottom and from ancient glaciers, and the use of radioactive isotopes. Findings of Earth history include the existence of life as early as 3.5 billion years ago and major changes in the composition of Earth’s atmosphere.
Evidence for one-celled forms of life-the bacteria-extends back billions of years. The appearance of life on Earth caused dramatic changes in the composition of Earth's atmosphere, which did not originally contain oxygen.