Oceans of Earth
the acknowledged worlds both in our solar system and circling
distant stars, Earth is the only planet known to have liquid oceans.
And it's probably no coincidence, either, that our world is the
only planet we know of that also harbors life.
we have chosen the moniker "Earth" for our planet, it might be
more appropriately named "Ocean," because water covers more than
72% of the globe's surface. The amount of water in Earth's seas
is staggering: around 310 million cubic miles (1.3 billion cubic
km). The deepest part of the ocean is over 6.8 miles (11km) below
the surface, and its average depth is 12,080 feet (3,682 m).
310 million cubic miles (1.3 billion cubic km).
Depth: 12,080 feet (3,682 m).
Depth: 6.8 miles (11km).
of globe covered: 72%
4.2 billion years.
of species in the oceans: 700,000 - 1,000,000.
Earth is the only known world with liquid oceans.
are not exactly sure how Earth's oceans were formed. However,
they believe that there are several possible sources for the water.
Probably some of the water was trapped in the rocky parts of Earth
when the planet was formed from material drifting in space. This
water could have been in the form of ice or water trapped in a
clay-like material. It could have also been in the form of the
components of water (hydrogen and oxygen) which were trapped in
planet came together, it heated up and parts of the early earth
vaporized. Some of this vapor formed our planet's atmosphere.
Later, some of the water vapor in the hot atmosphere cooled down
enough to become liquid, turn into rain and fill the oceans.
the water in the oceans, however, may have come to Earth later
on in the form of meteorites. In its early years, the Earth was
bombarded with many meteorites that carried a significant amount
of H2O. A bit later in its history comets, which are
basically "dirty snowballs," may have hit the planet also adding
to the oceans.
of the type of water found in comets and meteorites have shown,
however, that comet water is rich in deuterium and meteorite water
is rich in xenon. Ocean water has less of both of these materials,
suggesting that comets and meteorites only played a minor part
in adding to the world's early seas.
call our plant Earth, but since the surface is 72%
covered with water, a more accurate name might be Ocean.
we know for sure, however, is that our planet continues to release
more water vapor into the atmosphere through volcanic eruptions.
This water vapor will eventually turn to rain and find its way
into the oceans. In turn, some of the water in the ocean will
get pulled back in the solid part of our planet as the continental
plates under the ocean are pulled back under the surface of the
Earth, taking a bit of the ocean with them.
what is more amazing than just our planet having oceans is that
it has managed to keep them liquid over such a long period. This
is mainly due to the Earth's temperature. If our planet was closer
to the sun, like Venus, it likely would have never cooled down
enough for water to become liquid on the surface. Instead, the
globe would be like Venus: a hot, dry surface where the temperatures
are high enough to melt lead.
have found evidence that liquid water could be found on Earth
as long ago as 4.2 billion years. It is thought that Mars might
have had oceans in its early history, too, covering as much as
two thirds of the planet. As Mars cooled, however, they disappeared.
They may have become frozen under a layer of soil and rock, or
disappeared into the atmosphere and were eventually lost into
space. Today, Earth is the only known planet that has large, stable
bodies of liquid water on its surface, though some moons of the
outer planets, like Enceladus or Europa, may have liquid water
under an icy crust.
was once thought to also have extensive oceans that are
now either frozen below a dry surface or have evaporated
into space. (NASA)
as we know it requires water. This makes scientists suspect that
life on Earth may have begun in the oceans. In 1979 researchers
discovered the existence of deep sea hydrothermal vents. These
vents release hot gaseous substances from underground into the
water. The scientists noted that around these vents in the temperate
region between the hot gasses and freezing water, ecosystems containing
various types of fish, worms, crabs, bacteria and other organisms
have formed. They speculate that 3.7 billion years ago these places
may have provided the perfect place for life to start. Experiments
have shown that heat, pressure and the chemicals coming out of
the vents can create the right conditions for the organic compounds
needed for life to form.
or not life began in the oceans it is clear that the oceans were
the home of some of Earth's earliest life forms. Today, scientists
estimate that 50% of all life on Earth lives in the oceans. It
is the home of billions of plants and animals most of which live
near the sunlit surface. Some of the most abundant and smallest
life in the seas are phytoplankton. These are typically tiny single-celled,
plants that float and drift throughout the surface waters.
creature in the ocean, in fact on the entire Earth, is the blue
whale. This aquatic mammal can run almost 100 feet (30m) in length
and weigh 170 tons. In between these two extremes there is estimated
to be between 700,000 and one million species of life living in
the seas. By some estimates two-thirds of them have yet to be
named and described by science.
reefs are some of the most diverse ecosystems in the Oceans.
(Jim Maragos/U.S. Fish and Wildlife Service
licensed under the Creative Commons Attribution 2.0 Generic
sea-life is found in the coral reefs that lie in the ocean's shallows.
Coral reefs are underwater structures formed out of calcium carbonate
which is secreted by corals. Corals are tiny marine animals that
attach themselves permanently to a location as part of a colony
of similar creatures. When each generation of coral dies, it leaves
behind an exoskeleton on which other corals will attach and grow.
Over time these structures can become immense like the Great
Barrier Reef that stretches for some 1,600 miles (2600km)
along the coast of Australia.
reefs, often referred to as "rainforests of the sea", form some
of the most diverse ecosystems on Earth. Though they cover only
one tenth of one percent of the ocean floor, they support about
a quarter of all marine life.
coral reefs with their abundant life mostly exist in the shallow
regions of the sea where sunlight penetrates the surface, some
marine life can live in its darkest, coldest depths. In fact,
a few grow to great size. The giant isopod, a deep-sea scavenger
and relative of the tiny, common pill bug, can grow to a length
of over 30 inches (76cm) and weigh 3.7 pounds (1.7km).
deep-sea creatures that live in the dark depths can produce their
own bioluminescent light. The anglerfish has a fleshy growth that
protrudes from its head. The tip of this limb glows. The anglerfish
uses this lamp as a lure to bring curious prey, usually smaller
fish, within striking distance.
anglerfish lives in the deep ocean and attracts prey with
a glowing lure attached to its head. (Masaki
Miya et al. licensed under the Creative Commons Attribution
2.0 Generic license)
are five named oceans on Earth which lie between its continents.
By size from largest to smallest they are the Pacific Ocean that
separates Asia from the Americas then the Atlantic Ocean that
separates the Americas from Africa and Europe. There is also the
Indian Ocean that lies between Africa, Australia and the south
of Asia. Finally the two smallest oceans are the Southern Ocean,
which encircles Antarctica and the Arctic Ocean that covers the
North Pole between North America and Asia.
all these bodies of water are interconnected, scientists sometimes
refer to them as the World Ocean or global ocean. This term also
includes smaller salt water bodes like seas, gulfs and bays.
water is such a prerequisite for life, astronomers are anxious
to see if they can identify oceans on planets beyond our solar
system. So far, our instruments are not sensitive enough to see
if a planet around a distant star has liquid oceans, but scientists
think they have found several worlds that may be the proper distance
from their stars so that surface temperatures may allow for liquid
water. If this is true, the oceans of Earth, though they are unique
in our solar system, might be common in our galaxy. These distant
oceans may also harbor extra-terrestrial life.
divers explore an underwater wreck (Photo
by Albert kok licensed under the Creative Commons Attribution-Share
Alike 3.0 Unported, 2.5 Generic, 2.0 Generic and 1.0 Generic
Lee Krystek 2014. All Rights Reserved.