Material Cycles

Materials are made of matter which can be biotic or abiotic. Deep down, however, everything is atoms. When put together, these atoms (elements) somehow bring us to life, enabling the functioning of consciousness.

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    Without matter and materials, we could not grow and reproduce. Biological matter is a source of growth for cellular reproduction, although we technically could, at some point, reach a stage where we can create proteins, enzymes and everything else we need purely from abiotic elements and the right source of energy! keep reading to learn more about the material cycle, its definition, and more.

    Material Cycle Definition

    Materials are what objects and substances are made of and consist of atoms (elements) that combine. They are the tiny building blocks of everything that surrounds us. Natural processes often link together in sequences that create cycles, with the waste products of one process being the raw materials for other processes.

    The material cycle is the process by which materials are recycled into the environment.

    Material cycles refer to the way that materials move through ecosystems.

    For example, water (H2O) cycles through the environment, evaporating from oceans and rivers, condensing into clouds, and then falling back to Earth as precipitation.

    Similarly, carbon (C) and nitrogen (N) cycle through the atmosphere, plants, and animals.

    So then, you've guessed it... water is a material! So is anything else with a name, such as air.

    Closed vs Open-loop

    Currently, our large-scale systems are linear, especially the economic system. There is some cyclicality in several villages and communities worldwide, but for the most part, globalisation and industrialisation are functioning according to highly unsustainable parameters.

    Linear human economic models lead to resource depletion and waste generation. We are currently aiming to advance our economy into a circular one that better integrates reuse and recycling concepts.

    A circular economy focuses on closed-loop systems. These systems can process waste, heat, and other forms of energy, without allowing them to escape or dissipate into the atmosphere.

    The reliance on non-renewable energy resources, such as fossil fuels, cannot be sustainable. However, generally inefficient use of resources, including renewable resources, may accelerate depletion rates of raw or essential materials.

    Human use of mineral resources often involves dispersal after use or the production of mixtures from which separation is difficult.

    Monomers and Polymers

    What should we call a bunch of atoms that gather to form materials? For that, we have monomers and polymers!

    Monomers are the name given to individual small molecules that can be joined to form "larger monomer structures", known as polymers.

    Polystyrene is a synthetic (artificial) polymer made from styrene monomers (which occur naturally).

    In polymerisation, monomers are linked together by chemical bonds to create long chains. The type of monomer and the number of monomers in a chain determine the properties of the resulting polymer. Polymers can be natural (such as DNA, where the two strands that form a double helix are polymers) or synthetic, playing an essential role in everything from food packaging to construction materials.

    Polymers can usually only be safely reintegrated into the environment as monomers. They can be recycled back into monomers for industrial application through depolymerisation. Depolymerisation can be achieved through various means, including enzymes, acids (chemicals), or heat, but some processes are less sustainable than others.

    Material Cycle Example

    In the context of natural cyclicality, humans tend to take materials out of the biological systems, use them, separate their chemical constituents and return them in a different form to the environment. The environment may also lock certain elements, such as hydrocarbons (organic compounds), in the lithosphere, thus making those elements largely inaccessible to surface-dwelling lifeforms.

    Millions of dead leaves fall every season in forest ecosystems, and the trees need a lot of resources to regrow leaves when temperature and precipitation allow it. They need atoms and molecules that are essential to them. The trees re-extract these vital molecules, such as phosphorous (P), from their leaves before they fall each autumn!

    Every organism needs specific atoms and molecules to survive. Decay, enabled by the presence of oxygen, microorganisms, earthworms, etc., ensures that the chemical processes in the environment remain cyclical.

    Both fossil fuels and mineral resources are good examples of material cyclicality completed or accelerated by humans.

    Fossil Fuel Use

    Fossil fuels are formed through the slow process of dead animal and plant matter compression over millions of years. These fossil fuels are extracted through mining and drilling because they represent a high energy-density source.

    Energy-dense sources include simple molecules, such as hydrogen (H), and compounds like hydrocarbons, think petroleum.

    Fossil fuels have been essential to the development of human society but have also caused environmental damage.

    The burning of fossil fuels releases harmful emissions, such as nitrous oxides (N2O) and carbon dioxide (CO2), into the atmosphere upon combustion and during processing (e.g. the removal of ash from coal), which contribute to climate change. Additionally, the mining and extraction of fossil fuels negatively impact waterways or soil when heavy metals such as lead (Pb), mercury (Hg) and cadmium (Cd) are released from burning coal.

    Regarding safely disposing of waste, coal ash is easily transported by air and poses the greatest danger to human and environmental health. Waste or used oil (denatured fossil oil or contaminated with other substances) can be challenging to dispose of.

    Fossil fuels cannot be returned to the Earth after extraction.

    A (coal) power plant (in the US) that operates for 40 years will leave behind 9.6 million tons of toxic waste.1

    Mineral Resources Use

    Mineral resources refer to the components such as sands and other aggregates, metals (silver) and minerals (olivine) in Earth's crust. Minerals differ from each other chemically because they can be of different origins:

    • organic (biogenic): such as limestone constituents used in the cement industry,

    • inorganic: such as bauxite used to make steel and aluminium.

    Pyrite and sulphide minerals are habitats for acidophilic chemolithotrophs (a type of bacteria that love acidic environments).

    Some microorganisms are used to extract minerals, such as iron (Fe). This is known as biomining. They can also be used to recycle waste: using acids is usually toxic to the environment, so the microorganisms' metabolism can be used instead.

    Understanding the relationship between microorganisms and minerals will help develop effective bioremediation techniques and technologies.

    Bioremediation uses living organisms to remediate dead or polluted environments.

    We need living environments because an abiotic environment cycles materials slower than a living one. This is due to the living organisms facilitating biogeochemical cycles on Earth.

    Scrap mineral resources can come from:

    • Consumers who don't need used goods anymore, such as old cars.

    • Industries that manufacture or carry out other activities don't need the by-products, such as copper (Cu).

    The reasons why recycling may be difficult include the waiting times to get the product back to recover the materials from it (ranging from a few days for an aluminium can to many years for cars or computers), as well as dissipation, contamination or quality loss (e.g. dissipated salts on the ground melt or mix with other elements), and price restrictions (recycling might be more expensive than extracting the materials from the natural environment).

    Material Cycles in the Ecosystem

    All raw materials we have originated in natural ecosystems. As much as humans need these resources for their technosphere, the natural world needs to cycle some of them.

    The technosphere is a system made of all things technological and everything that interacts with it - including humans, our satellites, the internet, and airports or quarries!2

    Materials are being cycled continuously on Earth in a process called biogeochemical cycling or the nutrient cycle.

    Both refer to the circulation of the totality of the elements between living matter and the abiotic components of their environment.

    Microorganisms typically deliver or facilitate the cycling of numerous elements, such as oxygen (O2), carbon (C), phosphorous (P) and nitrogen (N).

    Methods through which microorganisms facilitate the biogeochemical cycles on Earth include nitrification, where plants convert ammonia (NH3) to nitrates (NO3-), or respiration, which is the release of energy from glucose.

    Waste and material cycling in ecosystems tend to be non-toxic. The damage toxic heavy metals such as uranium (U) and arsenic (As) do to the tissues is greater than the advantages they provide, and living organisms have not evolved to process them directly. Where potentially toxic materials exist, they tend to be bonded to other minerals, making them more stable, inert, and/or unlikely to leak.

    Because we are part of the same processes that shaped life for millions of years on Earth, what is toxic for our environment, is usually also harmful to us.

    Our ability to imitate natural systems and integrate them into our technosphere is sometimes called biomimicry and other times called innovation, especially when we come up with something previously unseen in nature. Our technology allows us to better dispose of waste and avoid toxicity build-up.

    UV filters, the use of clams to clean the sea bed, mineral water filtration systems, and sped-up rock mineralisation (CO2 being turned into a rock) are all examples of nature-inspired "clean-up" technologies.

    Some organisms and ecosystems depend entirely on the "waste" resources coming from somewhere else. What we see as waste, for them, is a valuable material or by-product.

    The food that reaches the bottom of the seas (known as the benthos) is sometimes called "marine snow". Marine snow is mainly made of particulate or powder, fine scraps of "dead matter and excreted waste" (detritus). The bottom-dwelling organisms depend more on the biogeochemical cycles because they tend to feed on secondary or tertiary sources.

    Material Cycles Advantages in the Ecosystem

    The industrial/consumer cycle is primarily about human activities and can be compared to the natural material cycling of our ecosystem.

    The industrial/consumer cycle refers to how materials are extracted from the environment (mining, logging, etc.), used by industry (manufacturing, etc.), and then returned to the environment (waste disposal).

    Unlike current industrial/consumer material cycles, however, natural ecosystem material cycles tend always to have the following advantages:

    • Biodegradability: the molecular constituents of the cycled materials can be used by organisms to sustain life processes and be recirculated.

    • Non-toxicity: monomers and individual molecules are pretty good at remaining "non-toxic" in our current atmosphere. Sometimes, they may be expelled in concentrated forms (venom, hydrothermal vents, etc.)

    • Symbiosis: bacteria, such as nitrogen-fixing bacteria, help bring inorganic materials into the organic world in exchange for receiving sugars from plants.

    • Evolution: existing materials can naturally evolve or branch out into new ones and develop unique characteristics.

    Scientists can always use existing molecules and materials in nature to develop new ones: kevlar is a high-strength material built synthetically from monomers in such a way that it can block ballistic impacts, for example, from bullets.


    The study of material cycles helps us to understand how materials move through the environment and how they can be reused or recycled. All molecules can become something else. Recycling is one way to help close the material cycle by reusing materials instead of discarding them. This ensures that valuable resources are not wasted and helps to protect the environment.

    Material Cycles - Key takeaways

    • Materials are made of atoms - the tiny elements that surround and make up everything around us. They have cycled continuously on Earth thanks to biotic and abiotic processes.

    • Water condensing from the clouds onto the ground, tree leaves falling and earthworms eating dead organic matter are all examples of materials being cycled and recycled.

    • Linear economic models, as opposed to circular ones, do not allow for the non-pollutive recirculation of matter because it does not invest enough resources into recycling research and facilities.

    • Both synthetic and natural materials exist, but humans can primarily produce polymers from the existing natural monomers they extract from plants, tar sands, etc.

    • Biodegradability, symbiosis and non-toxicity should be incorporated into the technosphere.


    References

    1. gem.wiki, Heavy metals and coal, 2021.
    2. UNESCO, The unbearable burden of the technosphere, 2019.
    Frequently Asked Questions about Material Cycles

    What are material cycles?

    Material cycles are the processes by which materials and their constituent elements are recycled back into the environment.  

    Why is the cycling of materials important in an ecosystem?

    The cycling of materials is important in an ecosystem because it helps sustain biotic life and conditions on Earth, by enabling oxygen, carbon, etc. to circulate.


    What are three materials that cycle through ecosystems?

    Three materials that cycle through ecosystems are ester monomers, nitrogen (N), or hydrogen (H).


    What are the different cycles of materials in the environment?

    Two different cycles of materials in the environment are the biogeochemical cycles and the man-made industrial-consumer cycle, 

    Test your knowledge with multiple choice flashcards

    Joined individual small molecules are called...

    Acidophilic chemolithotrophs are...

    Polystyrene is ... 

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