Earth system science

Earth system science is the study of four distinct but interconnected spheres within the earth’s natural system. This field of study focuses on the lithosphere, the hydrosphere, the biosphere, and the atmosphere. Earth system science studies the interactions among these systems, including the effects of natural and human-made events on these spheres.

Basic Principles

The field of Earth system science (ESS) is based on the notion that the lithosphere, the hydrosphere, the biosphere, and the atmosphere are interconnected. ESS involves the combination of a number of natural sciences, including chemistry, physics, biology, mathematics, and applied sciences, to frame and analyze Earth’s various processes and systems.

ESS developed relatively recently (it was first applied in the mid-1980s) to catalog the various elements of the planet and explain how these concepts related to one another. ESS also has demonstrated relevance in the study of natural disasters, such as research on hurricanes and earthquakes. ESS has become a useful tool for examining the effects of humans on the natural environment.

Background and History

In 1983, the advisory council of the National Aeronautics and Space Administration (NASA) established the Earth System Sciences Committee. This committee was charged with researching the earth’s many natural systems and processes and examining how they interact.

Scientists on the committee compared the committee’s endeavor to the study of the solar system, wherein such individual concepts as gravity, solar wind, magnetism, and the planets themselves are often examined in relation to one another. A member of the committee, Moustafa Chahine of NASA’s Jet Propulsion Laboratory, in a conversation with committee chair Francis Bretherton, argued that scientists had long focused on the solar system and that it was time to examine Earth’s system, too.

The purpose of the development of ESS was, in part, to better understand the scope and the contributing factors of natural disasters and events. For example, volcanic activity in the lithosphere can send soot into the atmosphere and thus dramatically influence the habitats of nearby organisms. ESS has proved useful in understanding how the earth has evolved through millions of years.

The Earth System Sciences Committee also became part of an effort to understand the concept of climate change and the effects humanity was having on the planet. In 1988, the committee released a groundbreaking report, “Earth System Science: A Program for Global Change.” This report included a schematic diagram that demonstrated how atmospheric, oceanic, biologic, geologic, and human factors interact, in some cases complementing one another and in other cases causing imbalances (such as climate change). The report became an important resource to which governmental and nongovernmental organizations pointed as they began to study global warming and climate change.

Elemental Interaction

ESS does not consider the four main elements of Earth’s system as independent. Rather, it considers these spheres to be overlapping and interdependent. Each sphere plays a role in a cycle of biogeochemical processes.

For example, a volcano releases water vapor through the lithosphere and into the atmosphere. The water returns to Earth in the form of rain and snow. The water is collected in the hydrosphere, from which plants and animals within the biosphere consume it. The organisms of the biosphere, in turn, return the water to the lithosphere in the form of waste, where it is broken down and recycled. The process then restarts.

Because ESS encompasses such a broad range of components, the study of this type of science requires the application of many different disciplines. Scientists must take and classify biological samples, conduct chemical analyses, utilize models of physics, develop and apply mathematical models, and conduct sociological surveys to better understand the processes that occur between each of the four main areas of ESS.

The Lithosphere

One of the main components on which ESS focuses is the lithosphere, which is the layer of solid and semisolid rock that forms Earth’s outer crust and uppermost mantle. The lithosphere is broken into giant tectonic plates, which are in constant motion atop the fluid asthenosphere (the softer and hotter layer just beneath the lithosphere).

When tectonic plates come into contact or release themselves from contact, the energy released along the edges of the plates (faults) causes earthquakes at the surface. Similarly, molten rock that is pushed outward through the lithosphere typically flows through fissures in the lithosphere and out through volcanoes.

Lithospheric activity implicates other systems within the ESS framework. For example, volcanic and seismic activity can significantly alter the flow of river water into and the topography of the surrounding area. In India, for example, a study of seismic and volcanic activity that occurred along a river basin through millions of years showed related changes in the terrain, forming hills and valleys and redirecting a river repeatedly.

In more dramatic fashion, a severe volcanic eruption can both level forests and kill countless people and animals. As was the case in 1980, when Mount St. Helens erupted in Washington State, however, volcanic activity also can create opportunities for life. The formerly devastated region has, since the eruption, seen more than 130 new ponds and lakes form, creating new ecosystems and habitats for wildlife.

The Hydrosphere

The hydrosphere, which contains all the planet’s liquid water in oceans, lakes, rivers, ponds, and streams, plays a pivotal role in ecosystems and provides habitats for a wide range of organisms. It is central to the hydrologic cycle, whereby water is collected in surface water from groundwater sources and ice and is evaporated and transferred into the atmosphere and returned to Earth as precipitation.

For the purposes of ESS, the hydrosphere also plays a major role in the interaction among Earth’s elemental spheres. The hydrosphere provides water for the biosphere, releases water vapor into the atmosphere, returns minerals, and is a vehicle for the transfer of various minerals and chemical compounds to and from the lithosphere.

The Biosphere

The biosphere is the component of the ESS model that houses the many different forms of life on Earth. The biosphere includes humans, as well as all animal and plant life. The biosphere even contains the most basic and simple forms of microscopic life, such as microbes and bacteria.

The effects that other elements of the ESS framework have on the biosphere have been well explored. The study of ecosystems, the extinction of animal species, and the damage caused to habitats and forests by natural disasters are all examples of the study of how the biosphere is affected by the other elements.

Scientists continually explore the effects of the biosphere on the other elements of Earth’s system. As technology improves, for example, scientists are able to study the role microbes play in the weathering and erosion processes, breaking down base rocks and creating and cycling minerals in the lithosphere. Furthermore, biologists are examining how the gases emitted by biologic species affect the atmosphere and, through weather conditions, the hydrosphere (where precipitation is deposited).

The Atmosphere

Since the development of ESS, increased attention has been paid to the study of global warming and how human-generated emissions are contributing to this problem. Millions of years before human life began, volcanic eruptions and even an occasional asteroid impact sent large volumes of carbon dioxide and other greenhouse gases high into Earth’s atmosphere, causing the earth’s temperature to rise, melting ice caps, and raising water levels. (Greenhouse gases are so named because they make it more difficult for heat to escape the earth, thereby keeping the planet warm; this is a process known as the greenhouse effect.) However, when carbon dioxide and other greenhouse gases are retained at the surface level, a cooling effect takes place, eventually leading to the formation of glaciers and ushering in a period known as an ice age.

The ESS model recognizes the interaction, in this case, between the atmosphere and other components of the overall terrestrial system. However, in the twenty-first century, greater attention has been paid to how humans (as part of the biosphere) are, through industry and other technological activities, rapidly releasing high volumes of greenhouse emissions into the atmosphere. The emission of such gasses accelerates global warming, causing the ice caps to melt and increasing water levels. Such a flood could have disastrous implications for the other elements of the ESS framework, including the destruction of many of the biosphere’s countless ecosystems and changing the chemical composition of the soil.

Additional Spheres

ESS continues to evolve as a science. Although the general consensus is that the Earth’s intertwining systems are localized to the hydrosphere, biosphere, atmosphere, and lithosphere, some scientists believe that other spheres should be included within this framework.

For example, some argue that the pedosphere must be considered a part of this discipline. The pedosphere is the layer of soil and organic matter that rests on the surface of the Earth. The pedosphere contains a vast number of minerals and chemical compounds essential for life on Earth. For this reason, it is often referred to as the skin of the planet, and like the skin of a living organism, it is influenced heavily by its relationship with the lithosphere, atmosphere, hydrosphere, and biosphere.

Others argue that another sphere should be considered a part of ESS: the cryosphere, which encompasses the earth’s frozen water (its glaciers, ice packs, icebergs, and arctic regions). The cryosphere is an important resource for the world’s water supply. It also is a critical indicator of global change. When icebergs, glaciers, and other frozen bodies melt under increasing temperatures, water levels rise. For this reason, scientists concerned with global warming carefully monitor the cryosphere for evidence of this trend.

Principal Terms

greenhouse effect: a process whereby carbon dioxide, methane, and other types of gas are released into the atmosphere, retaining the sun’s heat and causing global warming

lithosphere: the layer of solid and semisolid rock that forms Earth’s outer crust

pedosphere: the soil, rocks, and organic matter that rest on Earth’s surface

tectonic plates: fragmented plates that make up the lithosphere and that are in constant motion

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