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2: The Physical Environment

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    Learning Objectives
    • Outline the properties of water that are essential for life as we know it on Earth.
    • Describe the hydrologic cycle including the important reservoirs for water on Earth and processes that move water between reservoirs (or pools).
    • Define characteristics of soils and the factors that determine what type of soil develops in a given location.
    • Discuss the layers in Earth's atmosphere and distinguish between climate and weather in Ecology.
    • Illustrate the important factors in Earth's energy balance. 
    • Communicate the causes and climate consequences of Atmospheric and Oceanic circulation.
    • Delineate the natural causes of climate change on Earth.
    • Summarize some important changes in Earth's climate through geologic time.

    • 2.1: Properties of Water
      Do you ever wonder why scientists spend time looking for water on other planets? It is because water is essential to life, as we understand it; even minute traces of it on another planet can indicate that life could or did exist on that planet. Water is one of the more abundant molecules in living cells and the one most critical to life as we know it. Approximately 60–70 percent of your body is made up of water. Without it, life simply would not exist.
    • 2.2: Water (Hydrologic) Cycle
      The hydrosphere is the area of Earth where water movement and storage occurs. Water is found as a liquid on the surface (rivers, lakes, oceans) and beneath the surface (groundwater), as ice (polar ice caps and glaciers), and as water vapor in the atmosphere. Water reservoirs are the locations where water is stored. The hydrologic cycle describes how water moves around the world between different reservoirs and forms.
    • 2.3: Soils
      Soil is the outer loose layer that covers the Earth's surface and is the foundation for agriculture and forestry. Soils consist of organic material, inorganic material, water and air, and they differ in proportions of clay, silt, and sand. A soil profile is characterized by horizontal layers called horizons. Climate, organisms, topography, parent material, and time influence soil composition and formation.
    • 2.4: The Atmosphere
      The atmosphere, the gaseous layer that surrounds the earth, formed over four billion years ago and is held in place by the attractive forces of gravity. This section is a brief introduction to the layers of the atmosphere and the differences between climate and weather.
    • 2.5: Earth's Energy Balance
      Earth’s temperature depends on the balance between energy entering and leaving the planet. When incoming energy from the sun is absorbed, Earth warms. When energy is released from Earth into space, the planet cools. Many factors, both natural and human, can cause changes in Earth’s energy balance, including changes in greenhouse gasses; variations in the sun’s energy reaching Earth; and changes in the reflectivity of Earth’s atmosphere and surface.
    • 2.6: Atmospheric and Oceanic Circulation
      This section discusses the causes of Atmospheric and Oceanic circulation and the roles that Atmospheric and Oceanic circulation have in regulating Earth's climate and Energy balance.
    • 2.7: What Makes the Climate Change
      This section discusses the natural causes of changes in the Earth's climate over time.  These include changes in the radiation from the Sun, changes in the tilt of the Earth, changes in Earth's orbit, changes in greenhouse gas concentrations in the atmosphere, shifts in the location of land on earth through plate tectonics, and changes in ocean circulation.
    • 2.8: Past Climate Change
      Over Earth history, the climate has changed a lot. For example, during the Mesozoic Era, the Age of Dinosaurs, the climate was much warmer and carbon dioxide was abundant in the atmosphere. However, throughout the Cenozoic Era (65 Million years ago to today), the climate has been gradually cooling. This section summarizes some of these major past climate changes and how scientists study past climate change.


    This chapter describes the physical environment of the planet Earth and the importance of the physical environment for the field of Ecology. Sections 2.1 and 2.2 discuss important properties of water and they hydrologic cycle. Section 2.3 characterizes soils, their importance for ecology, and how they form.  Earth's atmosphere, energy balance and atmospheric and oceanic circulation are detailed in sections 2.4, 2.5, and 2.6.  Finally Sections 2.7 and 2.8 illustrate the natural causes of climate change on earth and some of the important past changes in Earth's climate. 

    2: The Physical Environment is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.

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