Any atmosphere contains living organisms

The global ecosystem

In recent years, environmental scientists have recognized more and more clearly that the earth must be viewed as a system: it cannot be understood as the sum of its parts, but only when the interactions are taken into account. These are produced by material cycles and energy flows.

The major subsystems of the Earth's ecosystem and the most important relationships between them. The sub-systems are interconnected by material cycles and energy flows. To clarify the special role of humans (>> more) this is shown separately. You can find out more about the individual subsystems on the following pages; you can also click directly on the illustration to go to the relevant pages. Own illustration.

A dynamic planet

If there were intelligent life forms somewhere in the universe beyond the earth, and if they were to devote themselves to our solar system while exploring space, they would immediately recognize that there is life on earth: our atmosphere would give us away. Without life, the chemically very reactive oxygen would combine with other substances and disappear from the atmosphere; Oxygen and the ozone it creates are therefore considered to be a sure sign of life on a planet.

The example shows: Life changes the composition of the air - and, as everyone knows, there is no life without air. This is not just the case with air and life: the earth is a dynamic planet that only gets its present-day appearance through a series of complex relationships between its subsystems (see figure above). These subsystems are also referred to as “spheres” according to older ideas of a shell model; so the atmosphere denotes the atmosphere of the earth; Hydrosphere the water resources of the earth, lithosphere the rocks and pedosphere the soils of the earth. Ultimately, the biosphere is the name given to the totality of living beings. The shell model has become obsolete since it became clear how the subsystems interpenetrate and influence one another; however, the names based on the model have become commonplace.

The dynamics of the subsystems even apply to seemingly as solid building blocks as the rocks. Since the discovery of >> plate tectonics, we have known that even stone slabs larger than continents are in motion, and that the rocks are in a cycle (>> the cycle of rocks). Some rocks were formed when living organisms (i.e. components of the biosphere) extracted carbon dioxide from the atmosphere to build up limestone casings that were eventually deposited on the sea floor and over time became sedimentary rocks (and thus "turned the sky into stone") Quote from Martin Redfern). Rocks are removed by rain (part of the hydrosphere) and wind (atmosphere) and can become part of the soil (the pedosphere), which in turn is the basis for the growth of many plants (which brings us back to the biosphere). Hopefully your head won't be buzzing with spheres yet, because there is still more: In the atmosphere there is an ozone layer that filters most of the sun's UV radiation from sunlight, making life on land possible in the first place The ozone layer is itself a product of life (>> The story of life on earth). Solar radiation heats the earth's surface and the heat is retained on earth by gases in the atmosphere; this warming also warms the air. Warm air expands, which increases the air pressure, this creates winds - which in turn take clouds (hydrosphere ...) with them and, through many complex interactions, form the >> climate of the earth; whereby mountains (lithosphere ...) can stand in the way of the clouds and influence the circulation of heat and moisture. Ocean currents also distribute heat (>> The global conveyor belt).

As if these relationships are not yet complex enough, one cannot understand the earth's ecosystem without looking at the external interactions. The most important source of energy is sunlight (>> more). Fluctuations in the earth's orbit around the sun, a slight wobbling of the earth's axis, cycles of the sun: all of them can seriously change the conditions for life on earth (>> climate history). Or let's look at the solar wind, a stream of charged particles that the sun is constantly hurling into space. The earth's magnetic field, the magnetosphere, protects us from this (>> The prerequisites for life on earth). This magnetic field is probably generated by convection currents in the liquid, outer iron core of the earth (>> journey into the interior of the earth).

The two paragraphs above describe just a few of the varied relationships; however, they give a first impression of the complex interrelationships of the earth subsystem. Only through these complex relationships do the subsystems remain stable - they are in dynamic equilibrium. To use a picture by Martin Redfern again: They are like a fountain that can retain its overall structure, but through which energy and matter constantly flow. Central elements of these relationships are energy flows and material cycles.

Our most important source of energy: solar radiation

The most important source of energy on earth is the sun (>> more); the earth receives 174.26 petawatts (= billion megawatts; >> more) solar radiation, which amounts to an amount of energy of 5.495 billion joules per year - far more than 10,000 times as much energy as humanity currently consumes. The solar radiation warms the earth to life-friendly temperatures (more on this under >> The conditions for life on earth and >> Climate); it drives the >> winds and the >> water cycle, and it is the most important Source of energy for life (In addition, some bacteria also use chemical energy, ie they "eat" rocks, minerals or gases; they are called "chemotrophic", but are hardly important for the energy balance of life). The basis for using the sun as a source of energy for life is probably the most important chemical reaction on earth - the Photosynthesis. Algae and plants can use sunlight and produce their own food from inorganic matter in the environment; During photosynthesis from the carbon dioxide in the air and from water, with the help of sunlight, they form sugar, which serves as a starting material for the production of energy and for the production of more complex organic compounds (in the technical language of ecologists these algae and plants are called - together with the chemotrophic bacteria - "(Primary) producers”); and all >> other living beings live from these organic compounds).

The most important reaction in the world: photosynthesis

The formula for photosynthesis seems simple: Each of six molecules of carbon dioxide (6 CO2) and water (6 H2O) a sugar molecule (glucose, C6H12O6), with six molecules of oxygen (6 O2) released:
Solar energy + carbon dioxide + water -> glucose + oxygen
Solar energy + 6 CO2 + 6 H.2O -> C6H12O6 + 6 O2.

In reality, the reaction is much more complex (>> more), the American chemist Melvin Calvin was awarded the Nobel Prize in 1961 for research. It takes place in the chloroplasts of algae and plants. Two pigments are involved, chlorophyll A and B, and one uses blue and the other red light. Green and yellow light are not needed and are reflected - therefore the algae and leaves are green. The solar energy absorbed by the pigments is converted into chemical energy, a molecule called adenosine triphosphate (abbreviated to ATP) is generated, which is a kind of “universal energy currency” of life (>> more): ATP drives numerous biochemical processes in living beings, under among other things, the structure of the sugar molecule and the incorporation of the sugar into more complex organic compounds.

(See also the page >> Photosynthesis.)

However, some of the energy from photosynthesis is not used to build up organic compounds, but to drive all kinds of work in the energy metabolism; such as the absorption of minerals or the transport of sugar and starch from the leaves to other parts of the plant. To do this, the sugars are broken down; this so-called cellular respiration takes place in the mitochondria and is, as it were, the counterpart to photosynthesis - oxygen is consumed and carbon dioxide is produced:
Glucose + oxygen -> carbon dioxide + water + energy
C.6H12O6 + 6 O2 -> 6 CO2 + 6 H.2O + energy.

Only part of the energy bound during photosynthesis remains in the form of complex organic substances in the plants; this part is known as net photosynthesis. From a global perspective, (only) about a third percent of the incident solar radiation is permanently converted into plant material (net primary production, >> here) - but this increases to about 120 to 130 billion tons of organic material on the mainland and others 105 to 115 billion tons built up in the ocean per year.


(Note: “Organic material” here means the dry weight - without the water always contained in living organisms. Often only the carbon content is given, which has an average ratio of 1: 2.2 to the total weight: the net primary production is therefore around 55 up to 60 billion tons of carbon on land and 48 to 52 billion tons of carbon in the sea. See also >> here)

The basis of human life

The 225 to 245 billion tons of organic material - or biomass - that are produced every year on the mainland and in the sea, are the basis of all further life and also of all human food (see the following section). They represent, so to speak, the interest of the producing ecosystems, their annual income. This production is unevenly distributed across the various ecosystems (>> more): Plants grow best where it is warm and humid. The most productive natural habitats are therefore wetlands and rainforests, while the arctic tundra, for example, accounts for just a quarter percent of the global production of biomass. In the sea, productivity is highest in the nutrient-rich estuaries, on the continental shelf and where nutrient-rich deep water rises (>> more).

Most productive, however, is intensively farmed arable land. We humans now use over 40 percent of the total biomass production on the mainland - and almost as much from the productive marine areas (>> more) - a value that impressively shows how strong human influence is on the earth's ecosystem as a whole.

From the flow of energy to food chains and cycles

Other organisms, such as fungi and animals, cannot produce organic matter themselves; To get to these, they either eat plants (herbivores), other animals (carnivores), both (omnivores) or the excretion products and the organic matter (decomposers, mostly fungi and bacteria) that arise when plants and animals die. The herbivores, carnivores and omnivores are for ecologists "Consumers”; the organisms that break down dead organic matter and break it down again into inorganic components "Destructors”. Their work closes the cycle of substances again.

Example of a Food chain. Figure modified from Raven et al., Environment (1993) and Murck, Envionemental Science (2005).

The cycles of the substances that form the organic material are part of global material cycles. Therefore, they are often much larger than most of us imagine: especially in the deserts, small dust particles are carried high into the atmosphere during sandstorms and transported over thousands of kilometers - around two billion tons every year. For example, the tropical rainforests of the Amazon are fertilized with mineral dust from the Sahara; Dust getting into the oceans alleviates the prevailing iron deficiency and thus promotes the growth of phytoplankton (more on global cycles >> below).

All stages of the food chain use a large part of the energy for their own energy metabolism (and ultimately convert it into heat), so that only a proportion of 5 to 20 percent is available for building structures Share of organic matter from stage to stage in the food chain. At the top of the food chain, only a fraction of the energy is available (see figure). Therefore, as producers, plants typically make up the majority of the biomass of an ecosystem, and herbivores are more numerous than carnivores - as is evident from the large herds of grazing animals in East Africa and the comparatively small number of big cats there.

Decreasing energy content in the food chain. Illustration after Murck,
Environmental Science (2005).

Since most living things have not just one source of food, but several - bears eat not only berries, but also salmon; People not only eat bread, but also meat - they are usually extremely complex in ecosystems Food webs formed, of which the food chains are only one part. (And of course both food chains and food webs are only abstract models of thought that are supposed to help you understand: you won't find either on a walk in the forest.)

More about the habitats of the earth here:
>> The habitats of the ocean
>> The habitats of the mainland

The second source of energy: heat from the interior of the earth

In addition to solar radiation, only one other natural source of energy plays a role: the heat from the earth's interior. This is based on two sources: the heat stored in the earth's core and the heat generated by the decay of radioactive substances in the earth's interior. The amount of energy is insignificant compared to solar radiation (less than 0.1 percent), but it is this energy that drives the processes of >> plate tectonics and thus determines the distribution of the continents and the seas.These processes also cause significant (and sometimes catastrophic) events such as volcanic eruptions, earthquakes and tsunamis for human cultures; as an energy source for the hot hydrothermal springs, it may also have driven the >> emergence of life; and even today there are living things that live on chemical energy deep inside the earth.

Since substances cannot leave the earth, they form cycles. Some are of particular importance global, biogeochemical circulatory systemssuch as the global carbon, nitrogen, sulfur and phosphorus cycles. These cycles connect rocks, soil, air, water and living things, as in the following example of the carbon cycle:

The global carbon cycle. The numbers indicate the carbon stores (black), the annual flows between the stores before the industrial revolution (blue) as well as the amount added by human activities since the beginning of the industrial revolution (red) and the additional carbon fluxes caused by humans every year (red and underlined). See the following text for an explanation. (The background image is from NASA, http://earthobservatory.nasa.gov/Library/CarbonCycle/carbon_cycle4.html)

On earth there is about 75 million billion tons of carbon. The vast majority (99.8 percent) of this is in the lithosphere: in limestone, in the form of fossil organic substances (e.g. in oil shale) or as coal, natural gas or crude oil. In comparison, the proportions in water (38,000 billion tons = 0.05 percent of the total occurrence), in the soil (1,580 billion tons = 0.002 percent of the total occurrence), in living things with about 800 billion tons and in the air with about 820 billion Tons (each about 0.001 percent of the total deposit) to be insignificant. They are not, as shown by >> climate change caused by the increase in the concentration of carbon dioxide (CO2) in the air.

Carbon dioxide is the most important carbon compound in the air; it is in equilibrium with the carbon dioxide dissolved in seawater - for every molecule in the air there are around 50 molecules of carbon dioxide in the oceans (the solubility changes with the water temperature: warm water can absorb less carbon dioxide). But all other carbon deposits are also connected to one another: via photosynthesis, breathing and the release of carbon during the breakdown of dead organic matter (see >> above), the carbon in air and water is connected to that in the biosphere. Some of them remain bound in plant and animal structures such as wood or lime shells. The oceans are particularly important here: if bound carbon sinks into the deep water, it will be largely withdrawn from the carbon cycle for the foreseeable future. Over time, this carbon can migrate to the lithosphere via sedimentation or the formation of fossil fuels. The annual nitrogen fluxes between the different deposits are shown in blue in the figure above (shown in billions of tons of carbon per year). But even the carbon in the lithosphere can get back into the atmosphere over long periods of time: Gradually through the weathering of rock; but also very suddenly, for example in the event of volcanic eruptions (the quantities are on average comparatively small and are around 100 million tons per year).

Recently, humans have massively intervened in this cycle (the red numbers in the figure above) by burning fossil fuels and burning forests to reclaim land. The carbon bound in them was released into the air (>> more). As a result, the carbon content in the air has increased from pre-industrial 597 billion tons to today's 820 billion tons (or better known as it is regularly read in the newspapers: the concentration of carbon dioxide from 280 ppm to 390 ppm today). The associated climate change makes the carbon cycle a focus of research on the earth's ecosystem.

>> moreon the carbon cycle & climate change

Nitrogen cycle

The earth's atmosphere consists of 78.1 percent nitrogen - 99 percent of the earth's nitrogen is located there as molecular nitrogen (N2). This hardly reacts chemically (nitrogen suffocates flames, hence its name). Living beings need nitrogen as a building block for proteins and the genetic material DNA, but plants and animals cannot use atmospheric nitrogen. Hence the availability of nitrogen limits biological production in many ecosystems. Plants can, however, absorb nitrogen as ammonium (NH4 +) or rather as nitrate (NO3-). “Nitrogen fixers” therefore play an important role in the nitrogen cycle: bacteria and cyanobacteria that convert atmospheric nitrogen into forms that can be absorbed by plants. These bacteria live, for example, in the roots of butterflies such as clover or lupine, which are therefore grown in agriculture as green manure. To a lesser extent, atmospheric nitrogen is also converted into nitrate and nitrogen oxides during thunderstorms. Once organically bound, over 90 percent of the nitrogen available for organisms circulates in a shortened cycle within the biomass.

Today nitrogen compounds are also released through industrial processes, for example in the form of >> nitrogen oxides, which are formed during combustion processes, or ammonium from agriculture. In contrast to molecular nitrogen, these compounds are reactive and are involved in the formation of “acid rain” and ozone. In the global nitrogen cycle, the targeted input in the form of nitrogen fertilizers also plays a major role today, today far more nitrogen is fixed by humans than through biological activities on the mainland.

The entire earth becomes one unit through the energy and material flows: It is surrounded by an air envelope, and the water cycle - like the great material cycles - also encompasses the entire earth. Living beings live in networks, the complexity of which we still do not fully understand; no living being can exist without numerous other living beings. This also applies to humans: Let us just think of our “intestinal flora” - a complex community of microorganisms that is just as vital to us as breathing air and drinking water, without which our food - which always comes from other living beings - does not provide us with all the nutrients we need could provide. Humans are part of the earth ecosystem, they emerged from it (more on this >> here), today they influence the cycles of the earth ecosystem more than any other species before them and more than the earth can tolerate (more on this> > here): The future therefore requires a rethink - the basis of all human activities is the functionality of the earth's ecosystem; Without functioning ecosystems, we also have no future economically (more on this >> here).

On the subject see also:
>> The cycle of rocks
>> Water cycle

Artificial ecosystem - biosphere 2

The 225 to 245 billion tons of organic material - or biomass - that are produced every year on the mainland and in the sea, are the basis of all further life and also of all human food (see the following section). They represent, so to speak, the interest of the producing ecosystems, their annual income. This production is unevenly distributed across the various ecosystems (>> more): Plants grow best where it is warm and humid. The most productive natural habitats are therefore wetlands and rainforests, while the arctic tundra, for example, accounts for just a quarter percent of the global production of biomass. In the sea, productivity is highest in the nutrient-rich estuaries, on the continental shelf and where nutrient-rich deep water rises (>> more).

How complex and incompletely understood ecosystems are is shown by the attempt, begun in Arizona in 1991, to find four men and four women in an artificially created ecosystem that cost 200 million dollars Biosphere 2to let live. Only energy should be supplied from the outside. Soon, however, the oxygen content of the air fell so sharply and the nitrogen oxide content rose so sharply that the residents were threatened with brain damage and had to be supplied with oxygen; food production was also insufficient. When cockroaches and yellow spider ants increased in an uncontrolled manner, the experiment was ended after almost 2 years - the earth's ecosystems are irreplaceable for the time being.

The global ecosystem - continue with:
>> The rock shell of the earth

To the >> overview

© Jürgen Paeger 2006 - 2017

Exploring the Earth's ecosystem began in 1983 when NASA set up an Earth System Sciences Committee, which published a first report in 1988 and showed how the subsystems interact. Without the term Earth System, the >> World Climate Research Program had been working on similar issues since 1980; Since 1988 the >> IPCC has also been working on global ecological issues in connection with climate change. Since 1987 there has been an >> International Geosphere - Biosphere Program to coordinate international research on the subject; At many universities today there are courses on the subject.

energy According to the first law of thermodynamics, it can neither be generated nor consumed, but only converted. The conversion takes place spontaneously only in the direction of higher to lower energy quality, from “order” to “disorder” - Second law of thermodynamics (>> more). The build-up of organic matter is the emergence of “order” from “disorder”, which is only possible when energy is used from “outside”; this can be chemical energy, but mostly it is photosynthesis. The ecological significance of photosynthesis consists in the fact that it converts energy from solar radiation into chemical energy, which "drives" the earthly ecosystems and their influence on the earth ecosystem (>> here).