The Sum of its Parts: Earth as a System

Africa is front and center in this image of Earth taken by a NASA camera on the Deep Space Climate Observatory (DSCOVR) satellite.


Imagine looking at a puzzle piece and trying to make sense of it. You might be able to make out the picture that is on it. At the very least, you can make out the colors and shapes. But imagine that you were able to fit that piece into a larger puzzle, figure out how it is connected to different shapes, and help us understand a larger picture. That’s analogous to the process of considering Earth as an integrated system instead of isolated parts. It allows us to explore our planet in a new way.

During the 1980s, satellites started to allow us to look at Earth from a more removed perspective. And scientists found that the parts of our planet we had been looking at up close – like forests, clouds, the ocean, glaciers, exploding volcanoes, and eroding rocks – were all connected. “From space we can view the Earth as a whole system, observe the net results of complex interactions, and begin to understand how the planet is changing in response to natural and human influences,” NASA explained in a 2003 report (see longer excerpt below.) With the satellite data and high-tech sensors on land and in the ocean, we are getting a sense of the larger puzzle. Researchers are discovering how their pieces of the puzzle are related to other pieces. These relationships between the puzzle pieces and the larger puzzle are interesting to people developing models of the Earth system, too. They hoped to explain as much as possible about how Earth worked through complex mathematical equations to make models as accurate as possible. And over the last few decades, they have been able to make Earth system models much more accurate as we have learned about interactions of the system.

The Sum of Its Parts

The parts of the Earth system are often described as "spheres" - the atmosphere, hydrosphere, biosphere, cryosphere, and geosphere. Educator Martin Ruzek notes that “the difficulty with any representation that divides the system is the danger of continuing a deconstructed perception of the holistic Earth system - in reality, no part of the Earth system can be considered in isolation from any other part.” When considering the parts of the Earth system, it is important not to lose track of the interactions between parts of the system.

While not technically on the planet, the Sun is a critical part of the Earth system too. Sometimes referred to as part of the exosphere (all space-related phenomena that affect Earth), energy from the Sun drives processes of the Earth system.

Bringing the Planet to the Classroom

While the parts of the Earth system (air, water, land, life, and ice) interact in various ways, they are traditionally covered separately in science classes. Often they are separate chapters of Earth science textbooks or in different textbooks altogether. For example, life is often not a part of Earth science classes at all. The division of scientific disciplines into chemistry, physics, and biology can be a challenge to teaching about Earth as an integrated system.

Despite the challenges, many areas of science education are moving towards fostering student understanding of the connections between different parts of the planet. Earth system science provides avenues to explore interdisciplinary science and ways to combine the natural and social sciences, arts, and culture. According to Martin Ruzek in his essay Earth System Science in a Nutshell (which can be found on the Starting Point: Teaching Entry-Level Geoscience website), “Earth system science offers natural avenues for combining research and education, and promotes inquiry into the complex world around us. The broad perspective that Earth system science offers promotes an inclusive approach to student interest - there is something for everyone.”

The Earth System and Climate Change

As the climate continues to warm, the Earth system changes. The ice of the cryosphere melts, sea level rises, and weather patterns and ecosystems change. And as the Earth system changes, the climate warms. Some of these changes even amplify the rate of global warming. A great way to highlight the interconnections in the Earth system with students is by exploring the factors that affect and are affected by Earth’s climate.

“Given the concerns that humankind is impacting the Earth's physical climate system, a broader concept of Earth as a system is emerging, including societal dimensions and the recognition that humanity plays an ever-increasing role in global change. Within this concept, knowledge from the traditional Earth science disciplines (geology, meteorology, oceanography, ecology, biology...) is being gleaned and integrated to form a physical basis for Earth System Science,” says Ruzek.

Ruzek continues by saying, “Earth system science fosters the synthesis of disciplinary knowledge into a holistic model of Earth with broader interdisciplinary relevance. However, the development both conceptually and physically of the Earth system model and its quantitative assessment in the classroom and laboratory is a continuing, formative process that requires nurturing and commitment to eclectic learning beyond one's discipline. The intersection of disciplinary specialties often provides the most fertile and interesting fields for study, but is easily sidetracked by traditional disciplinary interests.”

NASA's Definition of Earth System Science

“Earth is the only planet we know of that sustains life. Life on Earth is critically dependent on the abundance of water in all three phases - liquid, vapor, and ice. Carbon, existing in a variety of forms, is the very basis of life, and its greatest reservoir. In the atmosphere, carbon fully oxidized as carbon dioxide, fully reduced as methane, and in particulate form as black carbon soot, produces the greenhouse effect making Earth habitable. Earth's atmosphere and electromagnetic field protect the planet from harmful radiation while allowing useful radiation to reach the surface and sustain life. Earth exists within the Sun's zone of habitation, and with the moon, maintains the precise orbital inclination needed to produce our seasons.

These remarkable factors have contributed to Earth maintaining a temperature range conducive to the evolution of life for billions of years. The great circulation systems of Earth - water, carbon, and the nutrients-replenish what life needs and help regulate the climate system. Earth is a dynamic planet; the continents, atmosphere, oceans, ice, and life are ever-changing, ever interacting in myriad ways. These complex and interconnected processes comprise the Earth system, which forms the basis of the scientific research and space observation that we refer to as Earth system science.

In Earth system science, researchers take a contextual approach to scientific inquiry - they explore extreme weather events in the context of changing climate, earthquakes and volcanic eruptions in the context of tectonic shifts, and losses in biodiversity in the context of changes in Earth's ecosystems. This leads to the exploration and discovery of causes and effects in the environment. For instance, Earth system scientists have linked ocean temperatures and circulation to the moderate climate of northern Europe relative to its latitude, the annual changes of ozone concentration over Antarctica with the production of industrial refrigerants in the Northern Hemisphere, and the physics and chemistry of the atmosphere to air quality and fresh water availability.

From space, we can view the Earth as a whole system, observe the net results of complex interactions, and begin to understand how the planet is changing in response to natural and human influences. For example, Earth system science has begun to understand and quantify the effects of "forcings" on the climate system produced by the Sun's solar variability and the atmosphere's increasing concentrations of carbon dioxide and aerosols. The fact that researchers detect not just variability but trends in the key measures of Earth systems makes it imperative for us to ask, "How is the Earth system changing, and what are the consequences for life on Earth?" (Excerpt from NASA's Earth Science Enterprise Strategy, 2003)