How an Oxygen-Rich Atmosphere Developed Flashcards

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What was the level of oxygen in the Earth's early atmosphere compared with today?

The early atmosphere had almost no oxygen. Today the atmosphere is about 21% oxygen.

Which type of organisms were the first to release large amounts of oxygen into the atmosphere?

Simple organisms that do photosynthesis, such as algae in the oceans and early plants, were the first to release a lot of oxygen.

What is the word equation for photosynthesis?

carbon dioxide + water → glucose + oxygen (in the presence of light)

How did photosynthesis change the amount of oxygen in the atmosphere?

Photosynthesis made oxygen as a product. Over a very long time this caused the amount of oxygen in the air to increase.

How did photosynthesis affect the amount of carbon dioxide in the atmosphere?

Photosynthesis used carbon dioxide as a reactant. This slowly reduced the level of carbon dioxide in the air.

Why did it take millions of years for the atmosphere to become rich in oxygen?

At first there were only a few photosynthetic organisms. It took millions of years for enough of them to grow and release enough oxygen.

About what percentage of the Earth's atmosphere is oxygen today, after it became oxygen-rich?

About 21% of the atmosphere is oxygen today.

How did higher oxygen levels help animals to evolve?

Animals use oxygen for aerobic respiration. This process releases lots of energy, so more complex animals could live and evolve.

What is the ozone layer and how did rising oxygen levels allow it to form?

The ozone layer is a layer of ozone gas high in the atmosphere. It formed from oxygen. It blocks harmful ultraviolet radiation and helped life to survive on land.