The Evolution of Earth's Atmosphere

The Earth's atmosphere has evolved significantly over 4.6 billion years. Initially dominated by volcanic gases, it was primarily composed of carbon dioxide. As the Earth cooled, water vapor condensed to form oceans, which absorbed carbon dioxide, leading to the formation of sedimentary rocks. Photosynthesis by plants and algae further transformed the atmosphere by reducing carbon dioxide and increasing oxygen levels. Some plants became fossil fuels, storing carbon and preventing its return to the atmosphere. This process led to the current atmospheric composition of 80% nitrogen and 20% oxygen.

What were the primary gases released by volcanoes in the early Earth's atmosphere?

• Hydrogen and helium

• Oxygen and nitrogen

• Carbon dioxide and water vapor

• Methane and ammonia

How did the formation of oceans affect the carbon dioxide levels in the atmosphere?

• Increased carbon dioxide levels

• Decreased carbon dioxide levels

• Had no effect on carbon dioxide levels

• Increased oxygen levels

What process in plants and algae contributed to the increase of oxygen in the atmosphere?

• Photosynthesis

• Fermentation

• Decomposition

• Respiration

What happened to some plants and algae that prevented carbon dioxide from returning to the atmosphere?

• They evaporated into the atmosphere

• They decomposed completely

• They were covered in sediment and formed fossil fuels

• They were consumed by animals

Approximately how many years ago did the Earth's atmosphere reach its current composition?

• 4.6 billion years ago

• 1 billion years ago

• 2.7 billion years ago

• 200 million years ago