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What Are Natural Causes That Lead to Increased CO₂ Levels in the Carbon Cycle? — Reading Comprehension

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This NGSS-aligned middle school science passage explains natural causes that increase carbon dioxide levels in the carbon cycle. Students will learn how volcanic eruptions, forest fires, decomposition, and warmer oceans naturally release CO₂ into the atmosphere. The passage highlights important scientific v

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The carbon cycle is the movement of carbon between Earth's atmosphere, oceans, land, and living things. One important part of this cycle is carbon dioxide (CO₂), a gas found in the atmosphere. While humans can increase CO₂ through activities like burning fossil fuels, there are also natural causes that add CO₂ to the atmosphere. These natural events play a major role in keeping the carbon cycle balanced over time.

One natural cause of increased CO₂ is volcanic eruptions. When a volcano erupts, it releases gases trapped deep inside the Earth, including carbon dioxide. Even though volcanic eruptions are not common, they can send large amounts of CO₂ into the air very quickly.

Another natural cause is forest fires. When trees burn, the carbon stored in their trunks, branches, and leaves is released into the atmosphere as carbon dioxide. Forest fires can happen because of lightning strikes, especially during dry seasons. While forests also absorb CO₂ through photosynthesis, fires temporarily flip the process by releasing stored carbon back into the air.

Decomposition is another key source. When plants and animals die, decomposers like bacteria and fungi break them down. This process releases carbon dioxide as the organisms decay. In large ecosystems like wetlands or rainforests, decomposition is constantly adding CO₂ to the atmosphere.

In the ocean, warmer temperatures can cause carbon dioxide to be released from seawater into the air. The ocean normally stores a lot of carbon, but when the water warms up, it holds less gas, and CO₂ is released.

These natural sources are part of Earth’s normal carbon cycle. However, when they happen more often or more intensely—such as during long droughts or warming events—they can lead to higher CO₂ levels in the atmosphere.

Fun Fact: A single large volcanic eruption can release as much CO₂ as several hundred million cars running for a year!

What is the carbon cycle?

Water movement in natureEnergy flow in animalsCarbon moving through Earth’s systemsPlants using sunlight

Which gas is added to the atmosphere during volcanic eruptions?

OxygenHydrogenNitrogenCarbon dioxide

What natural event releases CO₂ from burning trees?

EarthquakesTornadoesForest firesHurricanes

How does decomposition add carbon dioxide to the air?

Plants stop growingBacteria release carbon as they break down dead matterAnimals breathe in CO₂Water traps carbon

Which process removes carbon dioxide from the atmosphere?

Volcanic eruptionsForest firesPhotosynthesisDecomposition

What happens to CO₂ when ocean water gets warmer?