The world is covered with water – a fact that has influenced our civilization in countless ways. The oceans of the world, in particular, have shaped human history, culture, and commerce. But just how much of the earth’s surface is covered by salt water? This article seeks to answer that question by exploring the definition of salt water, the earth’s surface area, the total amount of water on earth, the salinity of ocean water, and other factors that affect the coverage of salt water on our planet.
Definition of salt water
Salt water is the water that contains dissolved salts, minerals, and other substances. The most common salt in ocean water is sodium chloride (table salt), but there are also traces of other salts such as magnesium, calcium, and potassium. The concentration of salt in ocean water varies, but on average, it is about 3.5% (35 parts per thousand).
The earth’s surface area
The earth is a sphere with a diameter of about 12,742 kilometers (7,918 miles). Its surface area is about 510 million square kilometers (197 million square miles). However, about 70% of the earth’s surface is covered by water, leaving only 30% as land. This makes the earth a unique planet in our solar system, as no other planet has as much liquid water on its surface.
Total amount of water on earth
The total amount of water on earth is estimated to be about 1.4 billion cubic kilometers (326 million cubic miles). This includes all the water in the oceans, rivers, lakes, glaciers, groundwater, and atmosphere. However, the vast majority of this water (about 97.5%) is salt water, while only a small fraction (about 2.5%) is freshwater.
Salinity of ocean water
The salinity of ocean water is measured in parts per thousand (ppt) or practical salinity units (PSU). The average salinity of ocean water is about 35 ppt (or 35 PSU), but it can vary from about 32 ppt in some coastal areas to 37 ppt in some regions of the open ocean. The salinity of ocean water also varies with depth and location, due to factors such as evaporation, precipitation, temperature, and currents.
Calculating salt water coverage
To calculate the coverage of salt water on earth, we need to multiply the surface area of the earth by the percentage of the earth’s surface that is covered by water, and then multiply that result by the percentage of water that is salt water. Using these values, we get:
Salt water coverage = (70% of 510 million sq km) x (97.5% of 1.4 billion cu km)
= 357 million sq km x 1.365 billion cu km
= 487 million cubic kilometersPercentage of salt water on earth
Based on this calculation, we can say that about 97.2% of the world’s water is salt water, while only 2.8% is freshwater. In other words, salt water covers about 70.8% of the earth’s surface, while freshwater covers only about 2.5%. This means that most of the water on earth is not suitable for drinking, irrigation, or other human uses, as it is too salty or too inaccessible.
Comparison to freshwater coverage
To put these numbers in perspective, consider that the total volume of freshwater on earth is only about 35 million cubic kilometers, which is less than 3% of the total water on earth. Most of this freshwater is locked up in glaciers, ice caps, and underground aquifers, leaving only a small fraction as surface water, such as rivers, lakes, and wetlands. This makes freshwater a precious resource that must be carefully managed to meet the needs of a growing population.
Importance of salt water
Despite its high salinity, salt water is a vital part of the earth’s ecosystem. It supports a rich diversity of marine life, such as fish, whales, dolphins, and corals, as well as many species of birds, mammals, and reptiles that live near the coast. Salt water also plays an important role in regulating the earth’s climate and weather patterns, by absorbing and releasing heat and moisture, and by influencing ocean currents and atmospheric circulation.
Factors affecting salt water coverage
The coverage of salt water on earth is affected by various factors, both natural and human-made. These include climate change, which is causing sea levels to rise and threatening the survival of coastal ecosystems and human settlements; ocean acidification, which is reducing the ability of marine organisms to form shells and skeletons; overfishing, which is depleting fish stocks and disrupting food webs; pollution, which is contaminating the water and harming marine life and human health; and resource exploitation, which is causing conflicts over oil, gas, minerals, and other valuable substances.
Conclusion
In conclusion, salt water covers about 70.8% of the earth’s surface and contains about 97.2% of the world’s water, making it the dominant form of water on our planet. Despite its high salinity, salt water plays a vital role in sustaining life and shaping the earth’s environment. However, the increasing pressure of human activities on the oceans, combined with the effects of climate change, pose significant challenges to the health and resilience of marine ecosystems and the well-being of human societies. We must therefore work together to protect and restore the oceans, and to ensure that they remain a source of life, inspiration, and prosperity for generations to come.
References
- NOAA. (2021). What is the Salinity of Ocean Water? [Online]. Available at: https://www.noaa.gov/education/resource-collections/ocean-coasts-education-resources/ocean-chemistry/what-is-salinity-of-ocean-water (Accessed 14 May 2021).
- UNESCO. (2021). Water Scarcity. [Online]. Available at: http://www.unesco.org/new/en/natural-sciences/environment/water/wwap/facts-and-figures/water-scarcity/ (Accessed 14 May 2021).
- USGS. (2021). The Water in You: Water and the Human Body. [Online]. Available at: https://www.usgs.gov/special-topic/water-science-school/science/water-you-water-and-human-body?qt-science_center_objects=0#qt-science_center_objects (Accessed 14 May 2021).
