1A system is a network of parts, elements, or components that interact with and influence one another.
2 Systems receive and process inputs of energy, matter, or info and produce outputs of energy, matter, or info.
3 Systems do not have well-defined boundaries, which makes it difficult to decide where one system ends and another begins.
4 Systems may exchange energy, matter, and/or info with other systems.
5 Inputs into Earth's systems can include both solar energy and geothermal energy.
6 An event that is both a cause and an effect in a cyclical process is known as a feedback loop and can be either positive or negative.
7 A predator-prey relationship in which the two populations rise and fall in response to each other is an example of a negative feedback loop.
8 Negative feedback loops enhance stability by canceling an action once it reaches an extreme.
9 Erosion is an example of a positive feedback loop.
10 Positive feedback loops are relatively rare in nature but common in environmental systems that people have changed.
11 Scientists divide Earth into spheres, which are often described by their characteristics rather than by their location.
12 Earth's geosphere is made up of all the rocks at and below the surface of Earth.
13 The sphere of the Earth that consists of all the planet's living or once-living things and the nonliving parts of the environment with which they interact is the biosphere.
14 The outermost layer of Earth and geosphere is known as the crust.
15 The hydrosphere includes all water on Earth, including all forms of liquid, solid, and gas.
16 Earth spheres both overlap and interact.
17 An earthworm tunneling through the soil is an example of the biosphere interacting with the geosphere.