Elements of the Physical Environment

The environment can basically described to be everything that surrounds man, interacts with man and influences the way he exists. The elements therefore can be put to four different categories: the atmosphere which contains the air, gases, climate and water, the hydrosphere that includes water in oceans, seas, rivers and lakes, the lithosphere that describes things on the earth’s surface like rocks, soil and landforms and finally the biosphere that contains life or living things like the flora – plants and fauna – animals. Environment means the surroundings. Land, water, air, plants, animals, solid wastes and other things that are surrounding us constitute our environment. Man and environment are closely intertwined with each other, to maintain a balance or equilibrium in nature.

The Earth’s atmosphere is a thin layer of gases that surrounds the Earth. It made up of 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide, and very minimal amounts of other gases. This thin gaseous layer insulates the Earth from extreme temperatures; it keeps heat inside the atmosphere and it also blocks the Earth from much of the Sun’s incoming ultraviolet radiation. It’s approximated to be about 480 km thick, but most of the atmosphere (about 80%) is within 16 km of the surface of the Earth. There is no exact place where the atmosphere ends; it just gets thinner and thinner, until it merges with outer space. The atmospheric air pressure at sea level, is about equals 760 mm (29.92 inches) of mercury, 14.70 pounds per square inch the air pressure decreases. At an altitude of 10,000 feet, the air pressure is 10 pound per square inch and there is less oxygen to breathe. The atmosphere is made up of layers namely: the thermosphere which includes the exosphere and part of the ionosphere, the exosphere which is the outermost layer of the Earth’s atmosphere. The exosphere goes from about 640 km high to about 1,280 km, the ionosphere that starts at about 70-80 km high and continues for hundreds of kilometers like 640 km. It contains many ions and free electrons. The ions are created when sunlight hits atoms and tears off some electrons. Auroras occur in the ionosphere. Others include the mesosphere characterized by decreasing temperatures as you rise, the stratosphere characterized by slight temperature increase with altitude, the tropopause which sits between the stratosphere and the troposphere and finally the troposphere which is the lowest region in the earth’s atmosphere.

A hydrosphere is the total amount of water on a planet. The hydrosphere includes water that is on the surface of the planet, underground, and in the air. A planet’s hydrosphere can be liquid, vapor, or ice. On Earth, liquid water exists on the surface in the form of oceans, lakes and rivers. It also exists below ground—as groundwater, in wells and aquifers. Water vapor is most visible as clouds and fog. The frozen part of Earth’s hydrosphere is made of ice: glaciers, ice caps and icebergs. The frozen part of the hydrosphere has its own name, the cryosphere. Water moves through the hydrosphere in a cycle. Water collects in clouds, then falls to Earth in the form of rain or snow. This water collects in rivers, lakes and oceans. Then it evaporates into the atmosphere to start the cycle all over again. This is called the water cycle.

The lithosphere is the solid, outer part of the Earth. The lithosphere includes the brittle upper portion of the mantle and the crust, the outermost layers of Earth’s structure. It is bounded by the atmosphere above and the asthenosphere (another part of the upper mantle) below. The lithosphere is the most rigid of Earth’s layers. Although the rocks of the lithosphere are still considered elastic, they are not viscous. The asthenosphere is viscous, and the lithosphere-asthenosphere boundary (LAB) is the point where geologists and rheologists—scientists who study the flow of matter—mark the difference in ductility between the two layers of the upper mantle. Ductility measures a solid material’s ability to deform or stretch under stress. The lithosphere is far less ductile than the asthenosphere. The elasticity and ductility of the lithosphere depends on temperature, stress, and the curvature of the Earth itself. The lithosphere is also the coolest of Earth’s layers. In fact, some definitions of the lithosphere stress its ability to conduct heat associated with the convection taking place in the plastic mantle below the lithosphere. There are two types of lithosphere: oceanic lithosphere and continental lithosphere. Oceanic lithosphere is associated with oceanic crust, and is slightly denser than continental lithosphere. Continental lithosphere, associated with continental crust, can be much, much thicker than its oceanic cousin, stretching more than 200 kilometers (124 miles) below Earth’s surface.

The biosphere is made up of the parts of Earth where life exists. The biosphere extends from the deepest root systems of trees, to the dark environment of ocean trenches, to lush rain forests and high mountaintops. In all the categories of the elements in terms of spheres: atmosphere, hydrosphere and the lithosphere, the biosphere overlaps in all of these because there is life in every one of them. Although the biosphere measures about 20 kilometers from top to bottom, almost all life exists between about 500 meters below the ocean’s surface to about 6 kilometers above sea level. In this, the whole human, animal, bird and insect populations are contained.