The Earth’s Water

Natural Resources, Conservation, and Pollution

Our world contains many natural resources that we use to survive and some that we consume in the pursuit of our modern lifestyles. Air, water, and plant and animal life are all natural resources that we utilize in order to live. Rocks, minerals, and fossil fuels are examples of natural resources that we exploit to power our world and make technology possible. Wealth and status in the world economy is often determined by a nation’s access to natural resources. These resources can be classified as renewable, inexhaustible, and non-renewable.

Renewable resources are, as the name implies, resources that can be renewed, usually through careful management or conservation. Most of the renewable resources used in the world today come from plant and animal material. Our food supply relies on numerous renewable resources. As long as the rate at which we extract living material for our food supply is the same as the rate that it is replenished, we need not worry about the future of this type of resource. However, history provides many examples of situations where demand exceeded supply and a food resource was exhausted. In many nations, conservation laws are enforced and agricultural methods are followed to ensure the future availability of food resources. Some of the renewable resources used by our society go toward the production of items such as clothing and housing. Cotton grown in the southern United States has provided a renewable resource used to make clothing and other material for many years. Timber harvested from carefully managed forests can provide the raw materials to supply materials for future construction.

Saltwater and Freshwater

The vast majority of the hydrosphere (approximately 97.5%) is composed of salt water. The salinity of salt water, also called seawater, is about 3.5% on average. This means that roughly 35 grams of salts can be extracted from one liter of seawater. Of these salts, sodium chloride is the most common. Seawater also contains a wide variety of other chemical compounds. The following table shows the percentage by mass of elements that are commonly found in seawater.

One theory concerning the origins of salt in seawater dates back to the 18th century. The original thought was that salt and other minerals were delivered to the oceans by rivers after having been washed away by erosion and by leaching out of the ground. However, this was just half the story. Most of the salt in seawater has very ancient origins. Shortly after the formation of the oceans, sodium began to leach from the ocean floor. At the same time, hydrochloric acid was released from both volcanoes into the atmosphere and hydrothermal vents on the ocean floor. Sodium and chlorine combined in the prehistoric ocean to form sodium chloride, becoming the most abundant element in seawater.

The process through which sodium was leached from the ocean floors is no longer active in our oceans today. Although the oceanic leaching process no longer occurs, the salinity of the oceans has been stable for millions of years. This is because both chemical and geological processes are constantly recycling salt. Salt collects in sedimentary layers on the ocean floor. Eventually, these sedimentary layers are pushed under the continental masses at subduction zones by plate tectonics. The trapped salts in these layers make their way back to the surface through leaching and other processes, and are ultimately washed back into the sea.

All of the water in the hydrosphere contains some salt. Freshwater is defined as water that contains less than 0.5 parts per thousand of dissolved salts (by mass). By this definition, only about 2.5% of the world’s water supply is classified as freshwater. Glaciers and the polar ice caps currently store almost 95% of our planet’s freshwater supply. The remaining freshwater can be found in lakes, rivers, streams, aquifers, and in the atmosphere. Freshwater collects in reservoirs from precipitation of water vapor and through melting snow and ice.