What Is the Carbon Cycle? Definition, Steps, Facts, Earths Atmosphere CO2

What is the carbon cycle and why is it important?

Many people are confused about the impact of the carbon cycle on the plant, but the carbon cycle is one of the most simple and integral biological processes on the planet if you understand its purpose.

Carbon may not be the most abundant element on Earth, but it may very well be the most important.

There are many interesting facts about the carbon cycle, and this article explores components and steps of the carbon cycle as well as the impact humans have upon this life-sustaining process.

So, if you’re wondering, what is the carbon cycle, this guide provide a complete explanation.

What Is Carbon?

Carbon has been called “the backbone of life,” an apt name for an element found in all organic compounds.

Because elemental carbon readily bonds with other elements, oxygen in particular, carbon can be found in many forms.

Carbon’s most common form occurs when a single carbon atom bonds with two oxygen atoms and creates carbon dioxide (CO₂). According to the National Oceanic and Atmospheric Administration (NOAA), carbon dioxide is the fourth most prevalent gas in the Earth’s atmosphere, where it acts as a heat-trapping blanket around the planet.^3,17

The following table shows the primary elements’ contribution to the Earth’s atmospheric composition, according to the NOAA.³

Carbon is essential for all lifeforms, from the world’s largest extant mammal – the blue whale – to the smallest bacterial microbe. Yet, it is found most abundantly in the Earth’s crust.

Soil, rocks, and oceans act as “sinks” for carbon, where the carbon contained in organic matter is released through decomposition or transformed over millions of years through sedimentation.¹⁷

Carbon is an interesting element which can form a diverse group of mineral compounds. Carbon is responsible for fossil fuels such as oil, coal, and gasoline.

It is also the element which forms the beautiful and beloved diamond under precise conditions.¹⁷

Long-Term Carbon Storage and the “Slow Carbon Cycle”

According to the NASA Earth Observatory, most of the planet’s carbon is in long-term storage, contained within rocks and mineral deposits in the Earth’s crust.

Sometimes, this elemental carbon is released as carbon dioxide during volcanic eruptions. (To put this in perspective, humans release up to 300 times more carbon dioxide than volcanoes each year by burning fossil fuels.)

This is part of a process known as the slow carbon cycle.⁷

What Are Carbon ‘Sinks’?

Humans have carbon ‘sinks’ to thank for the amount of carbon on Earth that is trapped. A carbon ‘sink’ is anything (an organism, biome, microbiome, etc.) which absorbs more carbon dioxide than it releases.

Forests and oceans are the primary carbon reservoirs. The ocean alone absorbs up to 31% of atmospheric (CO₂), but increases of carbon dioxide in the ocean lead to more acidic seawater, a danger to less resilient marine life.²¹

One might assume that carbon is a primarily stationary or stagnant element, but it is actually in perpetual movement, through a process called the carbon cycle.

What Is the Carbon Cycle? (Carbon Cycle Explained)

Excess carbon in the atmosphere contributes to global warming, and as the effects of global warming become increasingly apparent, more people are seeking to understand “What is the carbon cycle?”

As discussed earlier, the ‘slow carbon cycle’ is a process whereby carbon gradually moves through rocks, soil, and the atmosphere over hundreds of millions of years. This process is so gradual that it is not an immediate concern for human beings.

The ‘fast carbon cycle’, on the other hand, is extremely crucial!

The ‘fast carbon cycle’ is the process by which elemental carbon, usually in the form of carbon dioxide, travels continually through organic matter, from the atmosphere to the Earth’s surface and back to the atmosphere. In other words, nature is constantly recycling carbon to be used again and again.³²

Interestingly, the amount of carbon on Earth is constant and does not fluctuate. However, the amount of atmospheric carbon is rapidly increasing as more and more carbon is released through human activity.³²

Continue reading to see the carbon cycle explained in depth, and learn why this biological process is so vital.

Carbon Cycle Diagram

Although the carbon cycle is critical to sustaining all life on Earth, it is actually a fairly basic process. View the depiction of its key elements in the simple carbon cycle diagram below.

This carbon cycle diagram illustrates how atmospheric carbon dioxide moves through organic matter.

1. First, atmospheric CO₂ is absorbed by plants and used to make food. The plants expel oxygen into the atmosphere but retain the majority of their carbon composition.
   The plants store the carbon until the time that they die and decompose or until they are consumed and their carbon content transferred to animals.
2. Next, many plants are consumed by animals in their entirety, including their carbon content. Animals expel much carbon back into the air through cellular respiration.
3. Then, plants and animals which have died begin the process of decomposition. Through decomposition, all of the organism’s stored carbon is released back into the soil.
4. Finally, the carbon dioxide in the soil may either be reabsorbed by plants or transported back to the atmosphere.¹⁷

What Is the Carbon Cycle’s Role in Supporting Life on Earth?

As part of the carbon cycle, carbon flows through all living things, but why is carbon necessary and what is the carbon cycle’s specific role in supporting life on Earth?

Most people are aware that trees and other plant life are very important in carbon uptake. But do they know that without the carbon cycle, there would be no food to eat? It is a fact that without the carbon cycle, plants would never have carbon dioxide they need to create carbohydrates.

All plants and the animals that rely on plants for food as well as the animals that rely on those animals for sustenance would all cease to exist! Additionally, carbon keeps the Earth warm enough to support life, is a building block of DNA, and fuels the majority of human industry.³²

Carbon Cycle Facts

The carbon cycle and its relationship to everything the human senses can observe is too often taken for granted. Here are 6 fascinating carbon cycle facts.

1. Carbon is one of the most abundant elements in the universe (4th most abundant to be exact!)¹¹
2. Less than 1% of the carbon on Earth is found in the atmosphere. Over 99% is stored in the Earth’s crust.⁵
3. The amount of carbon on Earth does not change; only the form and location changes. Human activity changes the amount of carbon in the atmosphere.¹
4. Without carbon dioxide in the atmosphere, the Earth would freeze and be uninhabitable.¹¹
5. Carbon dioxide can be trapped by various carbon ‘sinks,’ and the carbon sequestered by the oceans and along the coasts is called blue carbon.³²
6. Some new technologies remove carbon dioxide from the atmosphere through carbon sequestration.¹¹

What Is the Carbon Cycle: Carbon Cycle Steps and Carbon Cycle Elements

The carbon cycle can be broken down into several different processes, but these carbon cycle steps, while circular and continuous, are not necessarily sequential. The following illustration explores and summarizes some of the key carbon cycle elements.

This above illustration shows how the stages of carbon cycle is a complex and important process that plays a key role in maintaining a balanced and healthy environment.

Component 1: Photosynthesis (Photosynthesis Diagram Enlarged)

What is the carbon cycle’s most essential component? Most scientists would probably agree that photosynthesis is the most essential component of the carbon cycle, and some may even assert that it is the most critical chemical process on Earth.²⁹

During photosynthesis, plants absorb carbon dioxide and sunlight through their leaves. Plants contain a remarkable molecule, called chlorophyll, which facilitates sunlight absorption and also acts as a catalyst for chemical reactions.

This ability to harness the sun’s energy enables plants to combine the carbon dioxide from the air with water taken in via their roots to make sugars such as glucose and fructose – the food (energy) needed to grow and thrive.¹⁷

View this expanded photosynthesis diagram to see the process in action.

The sugars produced through photosynthesis are used by the plants to form more complex energy sources, such as proteins and starches. The starches and proteins and fats created are stored in a variety of ways, but most commonly in seeds, fruits, roots, and nuts.

These fuel not only the plants but the animals that eat the plants and the animals that eat those animals as well. In other words, photosynthesis is the biological process at the basis of the entire food chain.²⁹

Plants are the primary photosynthesizers in nature, but certain types of plants are better at it than others. The term ‘Net Primary Productivity’ is used to refer to the amount of energy stored by plants.

The Center For Sustainability and the Global Environment at the University of Wisconsin-Madison defines Net Primary Productivity (NPP) as “the net amount of energy a plant accumulates during a time period.” In other words, NPP is the energy that the plant is able to convert and store and does not include the energy lost during mitochondrial respiration.^8,19

Some biomes are incredibly efficient at storing energy while others are much less so. The following table rank orders the most productive biomes from most to least efficient.

* Data is in grams of dry biomass per year, inclusive of above and below ground NPP.⁸

Component 2: Respiration

Respiration in the carbon cycle releases carbon back into the atmosphere. Both plants and animals use a process called respiration to access energy from food.

Oxygen is consumed during respiration while carbon dioxide and water are discarded, making respiration an opposite process to photosynthesis.²⁴

Respiration occurs at both the cellular and whole organism level. With each exhale, CO₂ is released from the organism and back into the air.

Even plants release some carbon dioxide via respiration, though they retain the majority of their carbon throughout their lifespan.^10,17

Component 3: Decomposition/Sedimentation

Decomposition is the process by which organic matter breaks down. When a plant or tree dies, small organisms called decomposers (some insects, bacteria, fungi) break the organism down, undergoing their own respiration as they work.²⁸

As the organism decays, its carbon mass is transferred back into the soil where it continues as part of the fast carbon cycle.¹⁷

Occasionally, organic matter may be buried or covered by sediment before it has a chance to decompose. The process of sedimentation buries the organic matter deep underground where it is converted into fossil fuels through millions of years of heating and pressurization.

Sedimentation might occur during large scale natural disasters such as volcanic eruptions or small scale natural events such as mudslides or floods. Sedimentation shifts the carbon to the slow carbon cycle.¹⁷

Component 4: Combustion (What Is Combustion in the Carbon Cycle?)

The fourth component of the carbon cycle, combustion, is the one that has the greatest impact on global warming and climate change, but what is combustion in the carbon cycle? Combustion is the term used to describe the burning of organic matter when oxygen is present.

In other words, any time wood, oil, coal or any other type of fossil fuel is burned, combustion has occurred. Combustion releases large amounts of CO₂ into the atmosphere that would otherwise not be part of the carbon cycle.⁶

What Is the Relationship Between the Oxygen Cycle and the Carbon Cycle?

Many people may be wondering “What is the relationship between the oxygen cycle and the carbon cycle?” These two critical processes are closely intertwined.

The carbon and oxygen cycles are codependent upon one another and it is exactly this codependence that makes preservation of the delicate balance of the Earth’s ecosystems so paramount.

Oxygen is the second most prevalent element in the Earth’s atmosphere, comprising just over one-fifth. However, much of this is not pure, breathable O₂, as oxygen binds readily with other molecules, making up most of the Earth’s observable terrain

The waters which cover the majority of the Earth’s surface are made of single oxygen molecules bonded to two hydrogen molecules (H₂O). Meanwhile, sand is composed of two oxygen molecules bonded to a single silicon molecule (SiO₂).

Oxygen also commonly bonds to elements such as aluminum, iron, calcium, and magnesium, all of which are found in the Earth’s crust.²⁹

During the oxygen cycle, oxygen is pulled from the atmosphere to be used in various processes. Much atmospheric oxygen binds with other elements to form mineral compounds (Ex. iron oxide, commonly known as rust).

Oxygen is also drawn from the atmosphere to be used by plants and animals for cellular respiration. During respiration, living organisms use the oxygen molecules they absorb to fuel many cellular processes, such as converting food into energy, expelling CO₂.

Burning of coal and other fuels also requires a supply of oxygen. The oxygen is only replenished through photosynthesis, a crucial element of the carbon cycle.

CO₂ is produced as a waste product by animals during the oxygen cycle, and O₂ is in turn a waste product of the carbon cycle.²⁹ Some organisms and biomes are better at producing oxygen than others, and current estimates suggest that ocean organisms are responsible for more than half of Earth’s oxygen production.

In fact, a single species of microscopic bacteria called Prochlorococcus produces as much as 20% of the planet’s oxygen.

However, the vast populations of marine animals consume much of the oxygen produced by marine plant life. Land animals, including humans, obtain oxygen primarily from reservoirs in the atmosphere produced by the phytoplankton over millions of years rather than from current oxygen by-products of photosynthesis in the ocean or on land.¹³

What Is the Relationship Between the Carbon and Nitrogen Cycles?

Nitrogen is the most abundant element on Earth, comprising nearly 80% of the atmosphere. Although nitrogen gas is literally everywhere, it serves no purpose for most plants and animals as a gas.

However, plants and animals require nitrogen to form proteins, amino acids, and DNA.⁴ This is what makes the nitrogen cycle such a vital process.²⁰

The carbon and nitrogen cycles are similar in the sense that nitrogen gas (N₂) is pulled from the atmosphere in much the same way as carbon dioxide. However, in the nitrogen cycle, plants are not the primary actors.

Certain bacteria act as “nitrogen fixers” to absorb nitrogen and convert it into water soluble nitrates. While some plants have nitrogen fixing ability, bacteria are the critical players.

Nitrates help to fertilize soil and plant life and the nitrates are transferred from plants to animals upon consumption, providing animals the nitrogen needed. Nitrates are eventually converted back into nitrogen gas by an entirely different set of bacteria.

Although nitrates can increase the vigor of plantlife, they can also be dangerous when too much reaches a water supply, creating an imbalance in oxygen and carbon dioxide levels which can be detrimental to marine and land animals.²⁰

How Do Humans Affect the Carbon Cycle?

With climate change altering landscapes, changing habitats, and threatening many species with extinction, researchers are taking a closer look to answer the question “How do humans affect the carbon cycle?”

Unsurprisingly, human activity has a widespread impact on the carbon cycle and all of its aspects. Aside from the amounts of CO₂ being released into the atmosphere by increasing populations of humans, people are also affecting the carbon cycle through deliberate actions such as:²⁶

• Burning fossil fuels
• Releasing chemicals into the atmosphere
• Rapid expansion of farming, development, and industrial areas
• Deforestation

Explore each of these areas in more depth in the following sections.

How Much CO2 Do Humans Produce?

Many people have questioned “How much CO₂ do humans produce?” This question may bring to mind the carbon dioxide exhaled by humans during respiration.

A human being typically exhales more than 2 pounds of CO₂ daily, but humans are not actually producing this carbon dioxide. Rather, they are simply releasing their share of the carbon dioxide being continually recycled.

However, humans do produce CO₂ through specific actions such as the burning of fossil fuel and deforestation which create harmful CO₂ emissions. In fact, through combustion humans release nearly 20 times more carbon dioxide than they exhale.³⁴

Continue reading to find out more about the impact of these activities.

Burning Fossil Fuels

Nearly two centuries ago, the Industrial Revolution began, changing the way humans interacted with the environment and world around them.

During this period of time, industrial growth brought about drastic increases in 1) the conversion of natural and agricultural landscapes into industrial centers, 2) the production of machinery of all sizes which could expedite hours of manual labor, and 3) the burning of fossil fuels for energy to sustain and run both the industries and machinery.¹⁷

The vast majority of machines humans use today require some form of fuel to operate. Most cars, farm machinery, and airplanes burn fossil fuels such as gasoline or diesel to power their engines.

Power plants burn coal and oil to generate electricity for commercial and residential areas. Burning fossil fuels releases stored carbon directly into the atmosphere, where it becomes part of the carbon cycle.

So even though the absolute quantity of carbon on Earth does not change, human action transfers the carbon from a place where it is safely stored deep underground into the air that surrounds all life. Excess carbon creates a denser atmosphere which insulates the planet, trapping heat.¹⁷

Releasing Chemicals Into the Atmosphere

According to the Center For Science Education with the University Corporation for Atmospheric Research (UCAR), most air pollution stems from human activity. Burning of fossil fuels releases many harmful emissions aside from CO₂, including nitrogen oxides, sulfur dioxide and particulates.

Additionally, humans have synthesized harmful chemicals which are not naturally occurring. Some examples of chemicals released into the atmosphere as a result of human activity include:²

• Chlorofluorocarbons (CFCs) as coolants, aerosols, paint, and solvents
• Particulate matter (PMs) resulting from chemical reactions from power plant, factory, and vehicle emissions
• Nitrogen dioxide and Ozone (O₃) contributing to smog
• Sulfur dioxide (SO₂) contributing to acid rain

Rapid Expansion of Farming, Development, and Industrial Areas

Rapid expansion poses many problems for Earth’s ecosystems. Natural habitats and photo-synthesizers are destroyed and replaced by an agriculture, economy, and commerce reliant on fossil fuels.

(Image: Loren King³⁵)

Through rapid expansion, humans effectively flip the switch on the carbon cycle, changing whole areas that were once carbon sinks into carbon dioxide producers. Add the multitude of other pollutants generated and utilized in these areas to the equation, and it creates a rather desolate picture.

Deforestation

Deforestation occurs when large wooded areas are eliminated. Forests may be destroyed by cutting or burning, and there are various reasons why this may happen:¹⁷

• Disasters such as wildfires, often caused through human carelessness.
• Deliberate clearing of wooded areas for agricultural/commercial/industrial/residential use.
• Deliberate clearing of wooded areas for the purpose of using the wood of the trees.

Whatever the reason, deforestation is incredibly harmful for the environment. The following section examines in detail how deforestation impacts the carbon cycle.

What Is the Effect of Deforestation on the Carbon Cycle?

Deforestation is a critical issue in the world today and a huge contributor to global warming. But exactly what is the effect of deforestation on the carbon cycle?

The effect is compound, impacting the environment and carbon cycle from many different angles.

Because trees play such a critical role in the re-uptake of carbon dioxide from the atmosphere, the impact of deforestation on the carbon cycle is extreme. Every tree that is cut down is one fewer organism capable of absorbing and converting CO₂.

Thus, deforestation means less oxygen for animal life and a hotter carbon dioxide wrapped planet.

Deforestation also has the added impact of releasing additional carbon into the atmosphere. Some estimates suggest that as much as 15% of harmful greenhouse gasses are the result of deforestation.¹⁵

In the case of wildfires or forest burning, the effect is immediate. In the case where forests are cut down, the wood of the trees retains the carbon until it is processed or decomposed.

In other words, cut timber continues to store carbon until it breaks down or is processed for other purposes.¹⁷

Tips on How To Become Carbon Neutral

There are so many small and simple lifestyle changes within reach for any person looking for how to become carbon neutral. Small changes add up over time to produce a big impact.

After calculating their carbon footprint, readers can explore the following sections for ideas on becoming carbon neutral or even carbon negative!¹⁴

Choose Products Carefully

Many of the products people use on a daily basis are filled with harmful chemicals, both naturally occurring and synthetic. By this time, everyone is familiar with the harm caused by DDT (Dichlorodiphenyltrichloroethane) which was used for years in agriculture.

Small amounts of DDT can be found in the human bloodstream years and years later, per the Centers for Disease Control and Prevention. Although this insecticide has been banned in the U.S. since 1972, there are residual levels retained in permafrost and the water supply, and some countries still use DDT.

What can be learned from this misadventure in agriculture? Choose products carefully.

Products used in lawn care, salons, home cleaning, and skin care are often filled with harmful chemicals called volatile organic compounds (VOCs) that vaporize into the air and can cause allergy and respiratory issues in addition to their environmental effects. Aerosols, air fresheners, scented candles, paints, and chlorine bleach all contain chemicals that can cause harmful chemical reactions when released into the air.⁹

Read labels for warnings when purchasing products and avoid chemicals such as phthalates, ammonia, ethanolamine, tetrachloroethylene, sodium hydroxide, bleach, and diethanolamine. Also be wary of products with microbeads as these do not break down and almost always make their way into Earth’s waters where they are consumed by marine animals.

Another purchasing consideration for individuals involves reducing the consumption of single-use products. Purchasing reusable cutlery, cups, water bottles, bags, and straws can greatly reduce landfill waste.

Cutting back on items such as balloons, dryer sheets, and wet wipes can help protect the Earth’s wildlife, marine life in particular.¹⁸

Buy Local

What people buy is very important for environmental health, but a lesser known fact is that where people buy is also an important factor. Buying local reduces the carbon footprint in many ways.

(Image: Kenny Eliason³⁵)

Local products usually undergo significantly less processing (meaning less energy consumption) and use less packaging (meaning less waste). Buying from local markets and vendors reduces the burning of fossil fuels used in shipping and transporting goods.³¹

Supporting local businesses and farmers can also help prevent small companies from being replaced by large industries which are frequently energy hogs and energy wasters.

Consume Less Meat

Where people buy their food has a direct impact on the environment, but the type of food consumed is also a contributor.

Livestock farms require significantly more energy to maintain than crops, and the livestock themselves release methane and other greenhouse gases into the atmosphere.

Cutting back on meat consumption at an individual and family level helps to keep the food industry (crop to livestock ratio) in balance and limit harmful emissions produced by large-scale livestock operations.

However, if you operate a self sustaining farm, the meat you raise yourself will have a lower carbon footprint than exotic fruits and veggies that have to travel large distances to get to your location.

Conserve Resources

Many of the resources people use on a daily basis are taken for granted. There are small changes people can make inside their homes to conserve energy.

1. Use Less Water

• Take shorter showers
• Don’t overwater lawns
• Turn off water when washing dishes

2. Use Less Electricity

• Turn off lights and TVs when not in use
• Set thermostat warmer in summer and cooler in winter
• Unplug items when not in use
• Wash clothes in cold water

3. Make the Home More Energy Efficient

• Insulate attic spaces
• Weatherproof doors and windows
• Use blinds and curtains to keep the home cool in summer

Reduce Waste

Waste reduction benefits the environment in multiple ways. The best things to do to reduce waste are to:

• Reduce

Modern living is extremely wasteful, and the first step people can take to ameliorate this problem is to reduce consumption. If humans cut back on buying products that they don’t need and pay more attention to the amount of energy needed to fuel their lifestyles, they can make a difference.

• Reuse

So many products (Ex. dryer sheets, straws, paper towels, grocery bags) are made to be used once and disposed of. Look for items that are reusable, such as wool balls, silicone straws, bamboo towels, etc. to cut back on the energy costs of production and the chemical by-products of disposable materials.

• Recycle

Many items can be recycled to be remade into new products. While there is still an energy cost associated with processing recycled goods, it is not as high as the cost of mining new materials and making new products.

In fact, processing recycled material can save between 40 and 90% on production energy.¹²

• Compost

Composting is increasing in popularity for single-family households. Composting is a way to break down food waste at home rather than sending it to landfills.

There are multiple advantages to composting, such as reduction in landfill gases, retention of nutrients which decreases the need for chemical fertilizers in the garden, reduction of water run-off and pollutants.²² There are many easy-to-use composting systems for small backyards as well!

Explore Alternative Energy Sources

The U.S. Energy Information Administration lists five types of renewable energy sources.²³

• Biomass (energy from biofuels, solid waste, wood waste, and landfill gas)
• Hydropower
• Geothermal
• Wind
• Solar

Not all of these renewable energy sources are easy to harness at the individual level, but biofuels and hydropower have long been used by humans (think of hydro-powered mills). Although wind power is the biggest source of renewable energy in the U.S., solar power is probably the easiest alternative for the home.

More and more homes are being outfitted with solar panels to power daily life, and the tax breaks for going solar are significant. See the Office of Energy Efficiency & Renewable Energy’s Homeowner’s Guide to Going Solar for more information.

Explore Alternative Transportation

Transportation is a huge contributor to greenhouse gases. The vast majority of cars owned worldwide still burn fossil fuels for energy, releasing considerable amounts of harmful emissions directly into the atmosphere.

But travel is necessary, so what are the alternatives?

1. For short distances, consider walking or biking as an eco-friendly alternative to driving.
2. For longer distances, consider public transportation such as subways and buses.
3. When driving is necessary, consider carpooling with friends and neighbors.
4. Ensure that car maintenance is up to date, maximizing efficiency and avoid running the car idling for extended periods in parking lots and drive-thrus.
5. For individuals looking to purchase a new vehicle, electric vehicles are increasingly available and can save individuals money on maintenance and fuel in the long run.
6. Airplanes produce vast amounts of harmful emissions, so flying should be avoided when possible in favor of driving. However, sometimes flying is necessary, particularly when a trip is cross-country or international.
   When it is necessary to travel by air, look for direct flights rather than those with lay-overs, as takeoffs and landings can account for as much as 25% of emissions from a single flight.²⁷

Plant Trees

Planting trees may be the single best way to offset carbon emissions. According to the U.S. Department of Agriculture, a single tree can absorb close to 50 pounds of CO₂ from the atmosphere every year!³⁰

Planting trees is not difficult and is usually affordable. Individuals with land can consider planting tree farms or groves/stands of trees to benefit the Earth.

The trees which sequester the most carbon are typically those that are fast-growing and have large canopies. Mangroves, pines, oaks, and evergreens are all great at pulling CO₂ from the air.³³

The carbon cycle is a remarkable biological process that forms the basis of life on Earth. Through this cycle, all organic matter on the planet is interconnected and interdependent.

Even humans are important to the carbon cycle, and human activities have had a concerning impact upon atmospheric CO₂ levels.

Understanding the answer to the question, what is the carbon cycle, can help you take steps that will aid in its healthy operations.

Frequently Asked Questions About What Is the Carbon Cycle