The Roles of Water in Earth's Surface Processes

Earth is often called the water planet because of the abundance of liquid water on its surface and because water’s unique combination of physical and chemical properties is central to the earth’s dynamics. These properties include water’s exceptional capacity to absorb, store, and release large amounts of energy as it changes state; to transmit sunlight; to expand upon freezing; to dissolve and transport many materials; and to lower the viscosities and freezing points of the material when mixed with fluid rocks in the mantle. Each of these properties plays a role in how water affects other earth systems (e.g., ice expansion contributes to rock erosion, ocean thermal capacity contributes to moderating temperature variations). 

Biogeology: How do living organisms alter Earth’s processes and structures?

Evolution, including the emergence and extinction of species, is a natural and ongoing process that is shaped by Earth’s dynamic processes. The properties and conditions of the earth and its atmosphere affect the environments and conditions within which life emerged and evolved—for example, the range of frequencies of light that penetrate the atmosphere to the earth’s surface. Organisms continually evolve to new and often more complex forms as they adapt to new environments. The evolution and proliferation of living things have changed the makeup of Earth’s geosphere, hydrosphere, and atmosphere over geological time. Plants, algae, and microorganisms produced most of the oxygen (i.e., the O2) in the atmosphere through photosynthesis, and they enabled the formation of fossil fuels and types of sedimentary rocks. Microbes also changed the chemistry of Earth’s surface, and they continue to play a critical role in nutrient cycling (e.g., of nitrogen) in most ecosystems.
 

Natural Hazards: How do natural hazards affect individuals and societies?

Natural processes can cause sudden or gradual changes to Earth’s systems, some of which may adversely affect humans. Through observations and knowledge of historical events, people know where certain of these hazards—such as earthquakes, tsunamis, volcanic eruptions, severe weather, floods, and coastal erosion—are likely to occur. Understanding these kinds of hazards helps us to prepare for and respond to them.

While humans cannot eliminate natural hazards, they can take steps to reduce their impacts. For example, loss of life and economic costs have been greatly reduced by improving construction, developing warning systems, identifying and avoiding high-risk locations, and increasing community preparedness and response capability.

Global Climate Change: How do people model and predict the effects of human activities on Earth’s climate?

Global climate change, shown to be driven by both natural phenomena and by human activities, could have large consequences for all of Earth’s surface systems, including the
biosphere (see ESS3.C for a general discussion of climate). Humans are now so numerous and resource-dependent that their activities affect every part of the environment, from outer space and the stratosphere to the deepest ocean. However, by using science-based predictive models, humans can anticipate long-term change more effectively than ever before and plan accordingly.

Global changes usually happen too slowly for individuals to recognize, but accumulated human knowledge, together with further scientific research, can help people learn more about these challenges and guide their responses. For example, there are historical records of weather conditions and of the times when plants bloom, animals give birth or migrate, and lakes and rivers freeze and thaw. And scientists can deduce long-past climate conditions from such sources as fossils, pollen grains found in sediments, and isotope ratios in samples of ancient materials.