The Carbon Cycle for Middle School Science

2 days ago

4 min read

The Carbon Cycle describes how carbon moves through the environment. Carbon exists as a gas in the atmosphere and as a solid as a part of rocks. Carbon is also a part of plants and animals. It is incredibly important to life as we know it.

If you would like a copy of the picture book, you can get it along with the reading passage, flashcards, and comprehension activities at Teachers Pay Teachers.

The Carbon Cycle

The carbon cycle describes how carbon moves through the environment. Carbon is a special element because it is essential for life. On Earth, every organism is full of carbon. It is in sugars, proteins, fats, DNA, and almost every other part of an organism. Because carbon is both a part of life on Earth and the rocks on Earth, it has two cycles: the rapid cycle and the long-term cycle.

The rapid cycle shows how carbon moves through the atmosphere and organisms. When plants photosynthesize, they use light energy from the Sun to turn the carbon from carbon dioxide into sugar, which is made up of long chains of carbon.

Four things can happen to the carbon inside of plants after photosynthesis. First, the plant can use the carbon to live and grow. While plants make food through photosynthesis, they have to turn the food into energy to use it. Plants, like animals, use cellular respiration to convert sugar into carbon dioxide, water, and energy. They use the energy to grow and release the water and carbon dioxide as waste products. Plants return about half of the carbon dioxide they use in photosynthesis to the atmosphere through cellular respiration.

Second, if an animal eats the plant, the animal will convert the sugar from the plant into energy through cellular respiration. The animal will use the energy and release the water and carbon dioxide as waste products.

Third, if a plant burns in a forest fire, carbon from the plant is released as carbon dioxide and ash.

Fourth, if the plant, or the animal that eats the plant, dies, it will decay, and bacteria will use the sugar from the plant in cellular respiration and return some carbon to the atmosphere as carbon dioxide. The carbon not processed by the bacteria and other microorganisms becomes trapped in the soil.

The carbon trapped in the soil can become a part of the long-term cycle if it becomes sedimentary rock. While carbon in the rapid carbon cycle changes frequently, the carbon in the long-term cycle can stay in the same place for hundreds of millions of years.

In the long-term cycle, carbon moves from the atmosphere to the lithosphere through the rain. When the carbon, from carbon dioxide, and water combine, they form carbonic acid. Raindrops contain tiny amounts of this acid. Over millions of years, the carbonic acid in the rain dissolves rocks in a process called chemical weathering. The rocks release ions, including calcium ions. Rivers carry these ions to the ocean, where the calcium ions combine with dissolved carbon to form calcium carbonate.

Some animals that live in the ocean also produce calcium carbonate to make their shells and other hard body parts. Some of the calcium carbonate from the rocks and the animals falls to the ocean floor as sediments. Over millions of years, more and more sediments put pressure on the bottom layers, and they turn into sedimentary rock.

Sedimentary rock is one type of rock found in Earth's lithosphere. The solid rocks of the lithosphere make up giant plates that float on the hot, liquid magma of the asthenosphere in the mantle. Sometimes, these plates will collide, and the heavier plate dives underneath the other plate at a subduction zone. When the solid rock from the heavier plate reaches the mantle, the heat melts it, and it becomes a liquid rock called magma.

After the sedimentary rock melts, the carbon from the sediments floats around in the magma. Eventually, it is released back into the atmosphere when a volcano erupts and spews gases and ash into the sky.

The rapid and long-term carbon cycles overlap when organisms die, and the carbon from their bodies becomes trapped in rock. Sometimes, organisms, usually plants, die and are covered by other material so quickly that they don't have time to decay. Over millions of years, they become coal, oil, or natural gas, otherwise known as fossil fuels.

When we burn fossil fuels, we are causing more overlap between the rapid carbon cycle and the long-term carbon cycle. We are adding carbon to the atmosphere faster than plants or rain can remove it. As a result, more carbon dioxide dissolves in the ocean, making the water more acidic, which is dangerous for the plants and animals that live there. Carbon dioxide is also a greenhouse gas that traps heat from the Sun in the atmosphere.

Eventually, the carbon cycle will rebalance the carbon in the environment because a warmer Earth causes more water to evaporate and then fall as rain. Over millions of years, the rain will dissolve existing rocks and trap the excess carbon from the atmosphere in new sedimentary rocks at the bottom of the ocean. The Earth will recover, and scientists are working to ensure that humans will be around to see it.