Amanda is a retired educator with many years of experience teaching children of all ages and abilities in a wide range of contexts.
1. How the Oceans Were Formed
The oceans began to form many millions of years ago when the earth was still cooling and solidifying following its early molten, liquid state. The early oceans came about as a consequence of volcanic activity. We can define three clear stages in the formation of the oceans on the early Earth.
- As the young Earth cooled, volcanoes erupted, throwing out a mixture of gases that formed the early atmosphere
- When the atmosphere was saturated with water vapor, the vapor condensed, falling as rain. Rainwater began to collect in vast hollows
- The earth cooled and volcanic eruptions became fewer. For the last 100 million years the volume of water in the seas has stayed about the same
2. What Are Ocean Currents?
The map below shows the main ocean currents. Ocean currents are the directions of water flow around the world's seas. Currents are caused by the wind, by the spin of the earth, and by colder water sinking under warmer water.
3. Ocean Waves
Most waves are caused by wind blowing across the surface of the sea. The height and power of the waves depends on the speed of the wind and how far it has blown. Water in a wave appears to be moving forward, but in fact it is the kinetic energy which moves through the water, and the water itself rolls in circles.
What is a Wave?
Waves have two distinct phases called crests and troughs. As water circles upward it reaches the crest and as it rolls back down it forms the trough. At the shoreline, the base of a wave is held back and the water moves faster, toppling over as it reaches the land, causing "breakers".
Force of the Waves
When waves break on the shore, they exert a tremendous force. The weight of the sea hitting land can create pressures of more than 25 tonnes per square metre. That's 30 times as great as the pressure exerted on land by the average human foot.
What Causes Whirlpools?
Whirlpools are caused by a clash of tidal flows in a place where the sea floor is uneven. Currents rush toward each other, and, if they hit a rocky shelf on the sea floor, water surges upward, turning the surface into a seething mass.
4. Ocean Data and Facts
Total surface area
362 million square km (139.8 million square miles)
1.35 billion cubic km (324 million cubic miles)
Mean (average) depth
3.5 km (2.2 miles)
Weight of water
1.32 x 10^18 tonnes
% of Earth's water
-1.9 to 36 degrees Celsius (28 to 97 degrees Fahrenheit)
Freezing temperature of sea water
-1.9 degrees Celsius (28 degrees Fahrenheit)
Deepest known point
10,920 m (35,827 feet)
- More than 60% of the earth's surface is covered by water deeper than 1.6 km (1 mile)
- The average depth of the Pacific Ocean is 3.94 km (2.4 miles) and the average depth of the Atlantic Ocean is 3.57 km (2.2 miles)
- There's more gold dissolved in sea water than there is on land. The concentration is 0.000004 parts per million
- The ocean current called the Gulf Stream contains about 100 times as much water as the combined volume of all the rivers in the world
5. Minerals in the Oceans
Minerals dissolved from rocks by rivers are washed into the oceans. The most abundant are sodium and chlorine, which together form salt. The average salinity (saltiness) of the ocean is 33 to 38 parts salt per 1,000 parts water.
The ocean also contains:
- sulphate (7.94%)
- magnesium (3.66%)
- calcium (1.19%)
- and potassium (1.13%)
The total amount of salt in the world's oceans and seas would cover the entire continent of Europe to a depth of 5 km (3 miles).
6. What Are Islands?
Islands are those areas of land, smaller than continents, which are surrounded by water. They are found in seas, rivers, and lakes. Islands range in size from small mud and sand islands measuring only a few square metres to the largest, Greenland, which measures more than 2 million square km.
7. What Are the Four Types of Island?
Scientists define four main types of islands:
- Coral islands
- Volcanic islands
- Islands formed by a change in sea level
- Island arcs
Let's look at each in turn.
A coral island forms when corals (tiny marine organisms) grow up toward the surface of the ocean from an underwater platform in shallow water, such as the peak of a seamount. The coral skeletons build up over many years until they reach the surface.
Volcanoes that erupt beneath the ocean may eventually grow to reach the surface, where they emerge as islands. Volcanic islands often form close to tectonic plate boundaries.
Islands Formed By Changes in Sea Level
A rise in sea level, for example at the end of an ice age, may cut off an area of land from a continent, forming an island. Great Britain was formed in this way. Some pieces of land become islands temporarily during a high tide.
An Island Arc
An island arc is a chain of volcanic islands that usually forms close to a subduction zone. Some island arcs contain many thousands of islands. The Japanese islands were formed in this way.
8. The World's Largest Islands
|Name of Island||Ocean Location||Area in square km (square miles)|
Western Pacific Ocean
North West Pacific
9. How Coral Atolls Are Formed
An atoll is a ring-shaped coral island with a lagoon in its center. Atolls form when a coral reef builds up around a volcanic island, and the island subsequently sinks below sea level. As the island sinks, the coral continues to grow.
The illustration below shows the four stages of the formation of a coral atoll:
- A coral reef builds up, fringing a volcanic island
- As the island starts to sink, the coral continues to grow upward
- The island sinks further, coral forms around the beginnings of a lagoon
- The island disappears completely, leaving a coral atoll
10. Record-Breaking Oceans and Islands
- The greatest ocean current is the Antarctic Circumpolar Current (also known as the West Wind Drift Current), which flows at a rate of 130,000,000cu m (4.3 billion cu feet) per second
- The highest recorded wave (excluding seismic sea waves) was 34 m (112 feet) from trough to crest. It was recorded in 1933 en route from the Philippines to the USA
- The world's remotest island is Bouvet Island, about 1,700 km (1,056 miles) from the nearest land, Queen Maud Land on the coast of Eastern Antarctica
- The world's largest coral atoll is Kwajalein in the Marshall Islands, in the central Pacific Ocean. Its reef is 283 km (176 miles) long, and encloses a lagoon of 2,850 square km (1,100 square miles)
A Last Word
So, we've come to the end of our journey through the world's oceans and islands. I hope you've enjoyed reading these top 10 interesting and fun facts. I also hope you've learned something new. Scientists, both women and men, work hard every day throughout the world to discover more about our unique and beautiful world. And there's always something new to find out. Perhaps you'll be inspired to become a scientist, too, and help explore and protect our extraordinary planet.
© 2019 Amanda Littlejohn
Amanda Littlejohn (author) on January 21, 2019:
Thanks for reading and for your kind comments. Islands are fascinating, aren't they? And thank you for your great contribution. I had no idea people actually lived on Bouvet Island. How extraordinary! I wonder how on earth they survive?
Zia Uddin from UK on January 20, 2019:
Another fascinating article. At least I know Britain was formed by sea level changes. I was fascinated by Bouvet Island as the most remotest island in the world. I googled it and found that there is a small population of less than 300 people living there. Cheers.
Amanda Littlejohn (author) on January 19, 2019:
Thanks for your comment. You're right to point out that we have way too much garbage. And one of the greatest environmental threats is the problem of particles of plastic (and islands of it) contaminating not only the oceans themselves, but the fish which live in them. And which we then eat.
FlourishAnyway from USA on January 18, 2019:
I enjoyed this and learned a lot too. I didn’t know there were different types of islands. And all that salt! Too bad we can’t figure out a natural way to use salt to degrade garbage. We have a lot of both.