Question

components of the atmosphere

when earth formed 4.6 billion years ago from a hot mix of gases and solids, it had almost no atmosphere. the surface was molten. as earth cooled, an atmosphere formed, eventually evolving to its current form. many factors are thought to have contributed to the formation of the earth’s atmosphere. (choose 3)

• cyanobacteria are responsible for first adding oxygen to the earth’s atmosphere.

• the current atmosphere contains more carbon dioxide than the earliest atmosphere.

• the early earth atmosphere formed mainly from gases produced by cyanobacteria.

• the early earth atmosphere formed mainly from gases spewed from volcanoes.

• plants are responsible for bringing atmospheric oxygen up to its current level.

Explanation:

1. Cyanobacteria are responsible for first adding oxygen to the Earth’s atmosphere: Cyanobacteria (blue - green algae) are known to be the first organisms to perform photosynthesis, which releases oxygen. This was a key event in the evolution of the Earth's atmosphere, so this statement is correct.
2. The current atmosphere contains more carbon dioxide than the earliest atmosphere: The earliest atmosphere of the Earth was rich in carbon dioxide, methane, ammonia, etc. Over time, processes like photosynthesis (removing carbon dioxide) and the formation of carbonate rocks have reduced the amount of carbon dioxide in the current atmosphere. So this statement is incorrect.
3. The early Earth atmosphere formed mainly from gases produced by cyanobacteria: The early Earth's atmosphere was formed mainly from volcanic outgassing (gases like water vapor, carbon dioxide, sulfur dioxide, etc. spewed from volcanoes) long before cyanobacteria evolved. Cyanobacteria were responsible for adding oxygen later. So this statement is incorrect.
4. The early Earth atmosphere formed mainly from gases spewed from volcanoes: When the Earth was young and still cooling, volcanic activity was very intense. Volcanoes released large amounts of gases like water vapor, carbon dioxide, nitrogen - related gases, etc. which formed the early atmosphere. This statement is correct.
5. Plants are responsible for bringing atmospheric oxygen up to its current level: After the initial oxygen production by cyanobacteria, the evolution of plants (especially land plants) further increased the oxygen levels in the atmosphere through photosynthesis, bringing it to the current level. This statement is correct.

Answer:

• Cyanobacteria are responsible for first adding oxygen to the Earth’s atmosphere
• The early Earth atmosphere formed mainly from gases spewed from volcanoes
• Plants are responsible for bringing atmospheric oxygen up to its current level