Exercises: Origin of the Atmosphere, Hydrosphere, and Oxygen

Earth's first atmosphere was replaced by a second one produced mainly by volcanic outgassing. Define outgassing in your own words, and name two gases that volcanoes release in large amounts.

Scientists think that water-bearing comets and asteroids contributed to Earth's oceans. Identify the Earth system (geosphere, hydrosphere, atmosphere, or biosphere) that holds most of Earth's liquid water today, and state the process by which water vapor in the early atmosphere became liquid water on the surface.

Cyanobacteria were among the first organisms to release oxygen as a by-product. Name the process they used, and write the two main raw materials (reactants) of that process.

Mateo's notes say: "Early Earth's atmosphere was mostly oxygen and nitrogen, like today's." Explain why this statement is incorrect. In your answer, name the gas that dominated the atmosphere's oxygen-free composition besides water vapor and nitrogen, and say where it came from.

Compare volcanic outgassing and comet impacts as sources of Earth's water. For each source, describe what it supplied and give one reason scientists consider it important. Then explain why neither source alone is considered a complete explanation by every scientist.

Banded iron formations are layered rocks that formed in ancient oceans about 2.5 to 1.8 billion years ago. Dissolved iron reacted with oxygen and settled out as iron oxide layers. Explain what this evidence tells you about when and where oxygen was first produced, and why oxygen did not build up in the atmosphere immediately.

Aaliyah is writing a CER (claim, evidence, reasoning) response to the question: "How did early life change Earth's atmosphere?" Write a complete response. Your claim should address oxygen. Use at least two pieces of evidence (for example, banded iron formations, fossil stromatolites, or the rise of an ozone layer), and in your reasoning explain how the changing atmosphere affected the hydrosphere, the geosphere, and the biosphere.

Suppose atmospheric oxygen rose from almost 0% to about 21% of the atmosphere over roughly two billion years. Evaluate this statement: "The rise of oxygen was a gradual, steady increase that benefited all life." Give at least two reasons why it was neither purely steady nor beneficial to all organisms, and describe one way the new oxygen made a later development in life, such as complex cells that use oxygen, possible.