The Seas, a Repository of Life


On March 26, 2012, James Cameron, the movie director of Titanic and Avatar, successfully explored the Mariana Trench. The Mariana Trench, which is known as the deepest part of the world’s oceans, reaches a maximum depth of about 11 km [36,090 ft]. It is deeper than the height of Mt. Everest (8,848 m above sea level). Why is it that the expedition to the seas that are so familiar with us draws so much attention in the age of cutting-edge science, when we have even left human traces in space? It is because it has been hard for humans to explore the deep seas due to its high pressure, cold water temperature, and complete darkness. James Cameron made a six-hour expedition with the “Deepsea Challenger,” a deep-diving submersible designed to endure the water pressure down to 12 km [39,370 ft] below sea level, and he became the third person to reach the deepest point of the earth after the expedition of Jacques Piccard and Don Walsh in 1960. Only three people have been to the deep seas, and what amazes us is the fact that the geography of the bottom of the seas was revealed later than the geography of the moon’s front surface. The space containing as numerous mysteries as the universe is the seas.

Vast site of life

Oceanographers say that humans have explored only 5% of the whole oceans so far. About 71% of the earth face is covered with the oceans, and their areas reach 361 million km² [139 million mi2]. All the water on the earth makes about 1.369 billion km³, and the oceans hold about 97.3% of the earth’s water. The weight of the ocean water is estimated to be approximately 1.35 quintillion tons. Not only are the oceans vast, but are they also tremendously deep. The average depth of the oceans is 3,800 m [12,467 ft], which is a lot deeper than the average height of the lands, which is, 840 m [2,755 ft]. If the whole lands are dropped into the oceans, it will completely be submerged and still go 2,440 m [7,874 ft] further down the oceans. This shows how vast and deep the oceans are. It is no exaggeration to say that the earth is the planet of water or the planet of the oceans.

Countless living organisms live in the vast oceans, and the variety of today’s living organisms of the earth originated from it. As for the fish, the representative sea organisms, there are over 30,000 species, which take up the biggest portion among vertebrates. Compared with mammals, the number of species of fish is over six times more. This is not all. There are incredibly many different types of living organisms that the oceans embrace. Not only are there crustaceans like shrimps, shellfish, and corals, but also planktons that are hardly visible and all the way to blue whales, the largest animals on the earth. It is impossible to count the different types of living organisms living in the oceans. In the deep seas, new species of sea creatures are still being discovered. Oceanographers say that 95% of sea creatures are probably still unknown creatures with no names yet.

Temperature control device of the earth

The seas and the oceans are not only a living site for various organisms, but also an appreciated place that allows many living creatures on the land to live. There are severe changes of temperature on the land; it can go down to -90°C [-130°F] and reaches up to 70°C [158°F].

On the other hand, the temperature changes are much less in the seas; it is from -2°C [28.4°F] to 30°C [86°F]. Because water has high specific heat1), the temperature doesn’t easily change, compared with other materials. The amount of heat needed to raise the temperature of water by 1°C is 3,000 times more than the amount of heat needed to raise the same volume of the air by 1°C. This is how the seas can keep relatively stable temperature, compared with the land, and it can also store heat energy in the sea water. The seas and oceans also distribute the heat of the equator region to various regions of the earth through the enormous circulation system called ocean currents. Ocean currents move around like conveyor belts, carrying the heat energy from the sun. As the seas carry heat through a huge specific heat of water, the earth can have stable climates.

1) Specific heat: the amount of heat per unit mass required to raise the temperature by one degree Celsius

Let’s suppose that the earth had less water and that the size of the oceans was smaller than what it is now. The seas would not have been connected as one, and the ocean currents would not have been able to travel. Then the transportation of heat energy inside the earth would not have been so active like now, and we would have had to suffer extreme climates. When we think about these facts, we can say the seas are not only some blue water with lapping waves, but the base of life.

Resource of minerals

Sea water is salty and bitter unlike fresh water. It is because the sea water is a very complicated liquid with various types of minerals including salt. It is said that the amount of salt in all sea water of the earth is over 50 quadrillion tons, which explains why the oceans are called the earth’s largest warehouse for minerals. Sea creatures have been using minerals in the oceans effectively from a long time ago when mankind didn’t know their value yet. Until vanadium2) was discovered in the blood of sea cucumbers and of sea pineapples, man did not even know that the sea water contained vanadium. Cobalt3) was discovered in lobsters and mussels, and it was also discovered that mollusks use nickel4). The sea creatures had been using the minerals that man didn’t even know the names of, even before man started using them. On the contrary, man has only made limited success on extracting some minerals from the sea water. The techniques of man are in the beginner’s level, compared with the sea creatures.

  • 2) Vanadium: a chemical element with atomic number 23. It is a hard, silvery grey, ductile, and malleable transition metal. Steel with vanadium in it is used in high-speed airframes, jet engines, etc. Some animals and plants have vanadium in them, but its role in them is not clear yet.
  • 3) Cobalt: a chemical element with atomic number 27. It is a hard, silver-gray metal. It is used in the preparation of magnetic and high-strength alloys.
  • 4) Nickel: a chemical element with atomic number 28. It is used to make stainless steel, and also for alloy, coins, batteries, etc.

Purifying all the dirt

The seas receive all kinds of things from the land, but still do not rot. It’s because the seas continue to flow just like the saying that goes, “Flowing water does not rot.” More oxygen is absorbed in the flowing water than in stagnant water. Then the pollutants in the seas are oxidized, or the sea creatures including the microorganisms decompose the pollutants, using oxygen. Also, coastal wetlands, which are purifiers, play an important role in keeping the seas stable. The dense particles of coastal wetlands purify the seas, like a filter that lets water pass and filter out impurities. That’s not all. The microorganisms that live in coastal wetlands also eat away organic matters. The microorganisms’ ability to decompose pollutants within 1 km² [10.7 ft²] of a coastal wetland is equivalent to the work of a wastewater treatment plant. If the Amazon Rainforest is like the lungs of the earth, swamps are like the kidney of the earth.

Ever since the Industrial Revolution, the usage of fossil fuels has accelerated, which resulted in the dramatic increase of the level of the carbon dioxide in the atmosphere. Carbon dioxide which is a greenhouse gas increases the temperature of the earth. The seas absorb carbon dioxide, which is thought to be the main cause of the greenhouse effect, and also store it. Carbon dioxide in the atmosphere dissolves in the cold sea water and is stored in the deep ocean water, or is consumed through photosynthesis of phytoplankton. Phytoplankton in the ocean eats carbon dioxide and makes oxygen and produces about 70% of the oxygen in the atmosphere. This is far more than the amount of oxygen produced by the Amazon Rainforest which is called the lungs of the earth. Through the photosynthesis of phytoplankton, the level of carbon dioxide in the oceans lowers, and the level of oxygen rises. The amount of carbon dioxide produced by the usage of fossil fuels for the past 200 years from around the year 1800 is 224 billion tons. The sea water played an important role in suppressing the increase of the level of carbon dioxide in the air as 118 billion tons of them, which are about half of what was produced, were infiltrated into the sea water.

The seas are not only the living site of diverse creatures, but also make the environments of the earth suitable for numerous living creatures. The earth has an outstanding device that filters out the salty water and provides freshwater to the land. Annually, 425,000 km³ [112,000 U.S. gallon] of sea water evaporates by solar energy, and the vapors become clouds and rain down to the land. The freshwater that we use comes from the seas. The seas constantly make water and oxygen which are most important to the living organisms.

The earth is the only planet in the solar system with the seas of water, and it is the only lively planet where living organisms live. Despite many ongoing researches, any planet proper for living organisms like the earth has not been found. The Blue Marble is a famous image of the earth made in 1972, by the crew of the Apollo 17 spacecraft. The earth got the nickname because it looks like a blue marble thanks to the oceans surrounding its surface. It is a tremendous luck for mankind that the oceans surround the earth. It is not a coincidence that the chemical components of many organisms including humans are similar to those of the sea water. However, what we have known about the seas is only the tip of an iceberg.

The Blue Marble, a picture of the earth taken by the crew of the Apollo 17 spacecraft
Source: NASA / Wikimedia commons

There is a high chance that the seas which have a stable environment played the role of a womb for living organisms to be born for the first time. For a long time, the seas have been a repository of life for the earth. The seas even embrace sunken ships made of cold metal, and turn them into nests for the sea creatures. The seas are like a mother who embraces all things and blows life into them; the seas give infinite benefits to mankind and also willingly give people a corner of their hearts.

“How many are your works, O LORD! In wisdom you made them all; the earth is full of your creatures. There is the sea, vast and spacious, teeming with creatures beyond number—living things both large and small. There the ships go to and fro, and the leviathan, which you formed to frolic there.” Ps 104:24–26

Rachel Carson, The Sea Around Us, Oxford University Press, 1991
Yun Gyeong-cheol, Amazing Ocean Travel (in Korean, 대단한 바다여행), Pureungil, 2009
Park Dong-gon, Please Take Care of the Earth (in Korean, 지구를 부탁해), Science Books, 2011