An environment is made up of two fundamental categories: non-living (abiotic) factors like temperature, water, light, and nutrients, and living (biotic) factors like plants, animals, fungi, and microorganisms. Together, these components interact at every scale, from the thin layer of air around a single leaf to the entire biosphere. Understanding what goes into an environment means looking at its physical and chemical properties, the living things within it, the energy that drives it, and the cycles that keep it functioning.
Abiotic Factors: The Non-Living Foundation
Every environment rests on a set of non-living conditions that determine what can survive there. Temperature is one of the most powerful. Life on Earth can function across a surprisingly wide range, from about negative 15°C to around 113°C, though some microorganisms push those boundaries even further. The average surface temperature of Earth sits around 15°C under normal atmospheric pressure, which happens to support an extraordinary diversity of life.
Beyond temperature, several other physical and chemical variables shape an environment:
- Water availability. Liquid water is essential for metabolism. Bacteria, fungi, and other microscopic organisms need a minimum level of water activity (roughly 60% of pure water’s availability) to function at all.
- Light. Sunlight powers photosynthesis and drives weather patterns, ocean currents, and seasonal cycles.
- Nutrients. Minerals and chemical compounds in soil and water feed plant growth, which in turn supports everything above it in the food web.
- pH. The acidity or alkalinity of soil and water matters enormously. Some microbes thrive at pH values near zero (extremely acidic) or as high as 13 (extremely alkaline), but most larger organisms need a narrower range.
- Salinity. Salt concentration determines what can live in a body of water. Certain salt-loving microorganisms survive in solutions with 35% salt, far beyond what most life can tolerate.
These factors don’t exist in isolation. Temperature influences how much water evaporates. Water availability affects which nutrients dissolve and reach plant roots. The interplay between all of these conditions creates the specific character of a place.
Biotic Factors: The Living Web
The living side of an environment is organized in layers of increasing complexity. An individual organism is the smallest unit. A group of individuals from the same species living in the same area forms a population. Multiple populations of different species sharing a space and interacting with one another make up a community. When you combine that community with all the non-living factors around it, you have an ecosystem.
At the largest scale, the biosphere encompasses every ecosystem on Earth, from deep ocean vents to mountaintop glaciers. Each level depends on the ones below it. A forest ecosystem, for example, includes the trees, insects, birds, fungi, and soil bacteria (the community), plus the rainfall, soil chemistry, sunlight, and temperature that sustain them. Remove any one element and the whole system shifts.
Energy Flow and Nutrient Cycles
No environment exists without energy moving through it. Solar energy is the primary driver. It heats the atmosphere, oceans, and land surface, and it fuels photosynthesis in plants and algae. Wind patterns and ocean currents redistribute that heat around the globe, shaping regional climates. Water vapor carries latent heat through the atmosphere and releases it when clouds form, which is a major force behind weather and climate patterns.
While energy flows in one direction (from the sun, through organisms, and eventually lost as heat), matter cycles repeatedly. The nitrogen cycle moves nitrogen between the atmosphere, soil, bacteria, plants, and animals. Specialized soil bacteria convert atmospheric nitrogen gas into forms that plant roots can absorb, and those plants become food for animals. When organisms die, decomposers return that nitrogen to the soil and atmosphere.
Carbon follows its own loop. Atmospheric carbon dioxide dissolves in rainwater to form a weak acid that slowly breaks down rocks through chemical weathering. The released minerals wash into rivers and eventually settle on the ocean floor as carbonate sediments. Meanwhile, plants pull carbon dioxide directly from the air during photosynthesis, locking it into organic matter. These cycles connect every part of an environment, linking the atmosphere to the soil to the ocean to living tissue and back again.
Scale: Microenvironments and Macroenvironments
An environment can be as small as the space inside a hollow log or as vast as a continent. Scientists distinguish between microenvironments (the immediate surroundings of an organism) and macroenvironments (the broader conditions of the region). A terrarium is a useful example: the air temperature, humidity, and gas composition right next to the soil surface can differ significantly from conditions just a few feet above it.
This distinction matters in practical ways. Two animals housed in the same barn may experience very different microenvironments depending on ventilation, cage design, and position within the room. In nature, the sheltered underside of a rock has different temperature, moisture, and light conditions than the exposed surface inches away. Many organisms survive precisely because they exploit favorable microenvironments within harsher macroenvironments.
Biomes: Environments at the Global Scale
At the largest natural scale, Earth’s environments are classified into biomes, each defined primarily by climate and the vegetation adapted to it. Temperature and moisture are the two main sorting factors, and they’re shaped by latitude, elevation, and proximity to oceans.
- Tundra forms at high latitudes (above 60 degrees) or high altitudes, with permanently frozen soil and very short growing seasons.
- Boreal forests sit just south of tundra, with harsh winters, short summers, and mainly coniferous trees like spruce and pine.
- Temperate forests occupy mid-latitudes (roughly 40 to 65 degrees) where precipitation exceeds 750 mm per year, supporting deciduous trees that drop their leaves seasonally.
- Deserts receive less than 250 mm of rainfall annually and lose more water to evaporation than they gain.
- Tropical regions span roughly 5 to 35 degrees latitude, with warm temperatures year-round and distinct wet and dry seasons.
- Mediterranean environments occur between 30 and 45 degrees latitude, characterized by mild, wet winters and hot, dry summers.
Each biome represents a different combination of the same fundamental ingredients: temperature, water, light, soil, and the organisms that have adapted to those specific conditions over millennia.
The Built Environment
For humans, environment extends beyond the natural world. The built environment includes housing, roads, public transportation systems, commercial buildings, and community infrastructure. The CDC recognizes neighborhood and built environment as a key factor in health outcomes, encompassing housing quality, access to transportation, and even neighborhood safety.
Public transit systems, for instance, are critical infrastructure for children, older adults, and people with disabilities who can’t drive. When that infrastructure is damaged or absent, it doesn’t just create inconvenience. It reshapes the effective environment those people live in, limiting access to food, healthcare, and employment. The built environment layers on top of the natural one, and for most people on Earth, both contribute to daily life in ways that are hard to separate.
Human Activity as an Environmental Force
Humans have become the single most influential species on the planet. We’ve fundamentally altered the physical, chemical, and biological systems that every organism depends on. Scientists broadly agree that human activity, not natural processes, is the primary driver of accelerated global warming and large-scale changes to land use, water systems, atmospheric composition, and biodiversity.
This influence is now so pervasive that it functions as its own environmental component. Agriculture changes soil chemistry and water cycles. Urbanization replaces ecosystems with impervious surfaces. Industrial emissions alter atmospheric gas concentrations. When asking what makes up an environment today, human modification is as significant a factor as sunlight or rainfall in most regions of the world.