4-2 The Earth’s Life-Support Systems
What Are the Major Parts of the Earth’s Life-Support Systems? The Spheres of Life
The atmosphere is a thin envelope or membrane of air around the planet. Its inner layer, the troposphere, extends only about 17 kilometers (11 miles) above sea level. It contains most of the planet’s air, mostly nitrogen (78%) and oxygen (21%). The next layer, stretching 17–48 kilometers (11–30 miles) above the Earth’s surface, is the stratosphere. Its lower portion contains enough ozone (O3) to filter out most of the sun’s harmful ultraviolet radiation. This allows life to exist on land and in the surface layers of bodies of water.
The hydrosphere consists of the Earth’s water. It is found as liquid water (both surface and underground), ice (polar ice, icebergs, and ice in frozen soil layers called permafrost), and water vapour in the atmosphere.
The lithosphere is the Earth’s crust and upper mantle; the crust contains nonrenewable fossil fuels
The biosphere is the portion of the Earth in which living (biotic) organisms exist and interact with one another and with their nonliving (abiotic) environment.
What Sustains Life on Earth? Sun, Cycles, and Gravity
The one-way flow of high-quality energy from the sun, through materials and living things in their feeding interactions, into the environment as low-quality energy (mostly heat dispersed into air or water molecules at a low temperature), and eventually back into space as heat. No round-trips are allowed as energy cannot be recycled.
The cycling of matter (the atoms, ions, or molecules needed for survival by living organ- isms) through parts of the biosphere. Because the Earth is closed to significant inputs of matter from space, the Earth’s essentially fixed supply of nutrients must be recycled again and again for life to continue. Nutrient trips in ecosystems are round-trips.
Gravity, which allows the planet to hold onto its atmosphere and causes the downward movement of chemicals in the matter cycles.
How Does the Sun Help Sustain Life on Earth? A Distant Nuclear Fusion Reactor
Energy released by the gigantic nuclear fusion reactor we call the sun provides the light and heat needed to sustain the Earth’s life.
Much of the sun’s incoming energy is reflected away or absorbed by chemicals, dust, and clouds in the atmosphere, as shown in Figure 4-9. About 80% of the energy that gets through warms the troposphere and evaporates and cycles water through the biosphere. About 1% of this incoming energy generates winds, and green plants, algae, and bacteria use less than 0.1% to fuel photosynthesis.
🌱 4-3 Ecosystem Components
What Are Biomes and Aquatic Life Zones?Life on Land and at Sea
Biologists have classified the terrestrial (land) portion of the biosphere into biomes. They are large regions such as forests, deserts, and grasslands characterized by a distinct climate and specific species (especially vegetation) adapted to it.
Scientists divide the watery parts of the biosphere into aquatic life zones, each containing numerous ecosystems. Examples include freshwater life zones and ocean or marine life zones.