Earth’s biosphere is made up of just six chemical elements, enormous quantities of water, four types of large organic molecules, and a surprisingly thin layer of soil, rock, and air where all of it interacts. The total mass of all living things comes to roughly 550 gigatons of carbon, spread across a vertical range of about 20 kilometers from deep ocean to upper atmosphere. Understanding what this living layer is actually made of means looking at its chemistry, its major molecule types, the non-living materials it depends on, and where all of it sits on the planet.
Six Elements That Account for Nearly All Life
Living matter is built almost entirely from six elements: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. Scientists abbreviate them as CHNOPS. Carbon, hydrogen, nitrogen, and oxygen alone make up 96 to 98 percent of most cells by weight. Phosphorus adds about 1 percent (it’s critical for DNA, cell membranes, and energy transfer), and sulfur contributes roughly 0.2 percent, playing essential roles in proteins and certain metabolic helpers.
Beyond these six, life requires trace amounts of other elements. Iron, calcium, potassium, magnesium, zinc, and copper all show up in enzymes, bones, blood, and signaling systems. But by sheer mass, CHNOPS dominates. If you could weigh every organism on Earth and break it down to atoms, those six elements would account for more than 99 percent of the total.
Water: The Biosphere’s Dominant Material
By weight, the single most abundant material in the biosphere is water. Living organisms are, on average, about 70 percent water. Jellyfish push past 95 percent. Even trees, which seem solid, are roughly half water by mass. Water acts as the solvent for nearly every chemical reaction in cells, carries nutrients, regulates temperature, and gives structure to soft tissues. Without it, none of the organic chemistry that defines life would function.
Four Classes of Biological Molecules
The dry mass of every organism is dominated by four types of large carbon-based molecules: proteins, carbohydrates, lipids, and nucleic acids. These are the structural and functional building blocks of all cells.
Proteins do most of the work. They form muscle fibers, speed up chemical reactions, transport oxygen, and fight infections. Carbohydrates store quick energy (as sugars and starches) and provide structural support, like the cellulose in plant cell walls, which makes up a huge share of total biomass. Lipids, commonly known as fats, build cell membranes, store long-term energy, and insulate organisms. Nucleic acids, DNA and RNA, carry genetic instructions and direct the production of proteins.
Because plants make up roughly 450 of the biosphere’s 550 gigatons of carbon, cellulose and lignin (both carbohydrate-related compounds in wood and stems) are by far the most abundant organic molecules on the planet.
How Biomass Breaks Down by Kingdom
Not all life contributes equally to the biosphere’s material bulk. A landmark census published in the Proceedings of the National Academy of Sciences estimated that plants account for about 450 gigatons of carbon, making them the overwhelming majority. Bacteria come in second at roughly 70 gigatons, much of it hidden in deep soils and rock. Fungi contribute about 12 gigatons, archaea about 7, and protists (single-celled organisms like algae and amoebas) around 4. All animals on Earth, from whales to insects, total only about 2 gigatons of carbon.
This means that when you ask what the biosphere is “made of” in a material sense, the answer is mostly wood, leaves, and roots. Terrestrial plant tissue dominates everything else by a factor of more than 200 to 1 compared to animal life.
Minerals Made by Living Things
Organisms don’t just use organic molecules. Many species produce minerals, a process called biomineralization, and these hard materials are a significant part of the biosphere’s total mass. Calcium carbonate is the most widespread biomineral. It forms the shells of mollusks, the skeletons of corals, the tests of tiny marine organisms called foraminiferans, and even eggshells. Corals build their skeletons from a form of calcium carbonate called aragonite, growing about 40 micrometers per day. Hen eggshells reach 300 micrometers thick in just 24 hours, assembling from tiny particles of calcium carbonate that later crystallize into calcite.
Sea urchin teeth and spicules, mollusk nacre (mother of pearl), and the massive reef structures visible from space are all biomineral products. Other organisms produce silica (the glassy shells of diatoms), calcium phosphate (vertebrate bones and teeth), and iron oxides (used by certain bacteria for navigation). These materials cycle back into sedimentary rock over geological time, blurring the line between the biosphere and the Earth’s crust.
The Atmosphere’s Role
The biosphere constantly exchanges gases with the atmosphere, and several of those gases are themselves products or raw materials of life. Oxygen, produced by photosynthesis, makes up about 21 percent of the atmosphere and is consumed by nearly all animals and many microbes. Carbon dioxide, at much lower concentrations, is pulled in by plants and algae to build carbohydrates and is released back by all organisms during respiration.
Nitrogen gas makes up 78 percent of the atmosphere, but most organisms can’t use it directly. Certain soil bacteria convert it into usable forms like ammonia, feeding it into the food web. Soil microbes also emit nitric oxide, a reactive nitrogen compound that enters atmospheric chemistry cycles. Plants, in turn, absorb nitrogen dioxide and other oxidized nitrogen compounds through their leaves, acting as a sink that pulls reactive nitrogen back out of the air.
Soil: Where Living and Non-Living Materials Mix
Soil is the biosphere’s interface with rock, and its composition reflects that dual identity. By volume, soil is roughly 40 to 45 percent inorganic mineral particles (sand, silt, and clay derived from weathered rock), about 5 percent organic matter, and around 50 percent pore space filled with water and air. The organic fraction, called humus, consists of decomposing plant and animal tissue along with living and dead microorganisms. Humus binds soil particles together, retains moisture, stores nutrients, and provides energy for the vast microbial communities that live underground.
Sand particles range from 0.1 to 2 millimeters in diameter, silt from 0.002 to 0.1 millimeters, and clay particles are smaller than 0.002 millimeters. The ratio of these determines how well soil drains, holds nutrients, and supports root growth. This thin layer of mixed biological and geological material is where most terrestrial nutrient cycling happens, making it one of the most materially complex zones in the entire biosphere.
Life in Deep Rock
The biosphere extends well below the soil surface, into the deep crust itself. Microbial communities survive kilometers underground, relying on materials and energy sources completely independent of sunlight. In rocks rich in iron-bearing minerals like olivine and pyroxene, chemical reactions between water and rock produce molecular hydrogen, which microbes use as fuel. In formations containing radioactive elements like uranium-238 or potassium-40, the radiation splits water molecules into hydrogen and reactive oxygen species like hydrogen peroxide. That peroxide then reacts with sulfide minerals such as pyrite (iron sulfide) to produce sulfate, which other microbes use as an energy source.
In certain deep granitic and basaltic environments, these water-rock reactions also generate simple hydrocarbons. Methane seeping up from magmatic sources feeds specialized archaea hundreds of meters below the surface. These deep ecosystems are tiny by mass compared to surface life, but they reveal that the biosphere’s material basis extends to include rock minerals, radioactive elements, and dissolved gases that most people wouldn’t associate with living systems.
Human-Made Materials Now Rival the Biosphere
The total mass of all living things on Earth, including the water they contain, is approximately 1.1 teratonnes (1,100 gigatons). A 2020 study in Nature found that the total mass of everything humans have built, from concrete and steel to asphalt and plastic, crossed that same threshold around the year 2020. Human-made mass has been doubling roughly every 20 years, meaning that for every person alive, roughly the equivalent of their body weight in new manufactured material is produced each week. The biosphere is no longer the largest accumulation of organized material on the planet’s surface.