Approximately 71% of the Earth’s surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.
More than half of this area is over 3,000 metres (9,800 ft) deep. Average oceanic salinity is around 35 parts per thousand (‰) (3.5%), and nearly all seawater has a salinity in the range of 30 to 38 ‰. Scientists estimate that 230,000 marine species are currently known, but the total could be up to 10 times that number.
The major oceanic divisions are defined in part by the continents, various archipelagos, and other criteria. These divisions are (in descending order of size):
- Pacific Ocean, which separates Asia and Australia from the Americas
- Atlantic Ocean, which separates the Americas from Eurasia and Africa
- Indian Ocean, which washes upon southern Asia and separates Africa and Australia
- Antarctic Ocean, sometimes considered an extension of the Pacific, Atlantic and Indian Oceans, which encircles Antarctica.
- Arctic Ocean, sometimes considered a sea of the Atlantic, which covers much of the Arctic and washes upon northern North America and Eurasia.
The Pacific and Atlantic may be further subdivided by the equator into northern and southern portions. Smaller regions of the oceans are called seas, gulfs, bays, straits and other names.
Geologically, an ocean is an area of oceanic crust covered by water. Oceanic crust is the thin layer of solidified volcanic basalt that covers the Earth’s mantle. Continental crust is thicker but less dense. From this perspective, the earth has three oceans: the World Ocean, the Caspian Sea, and Black Sea. The Mediterranean Sea is at times a discrete ocean, because tectonic plate movement has repeatedly broken its connection to the World Ocean through the Strait of Gibraltar. The Black Sea is connected to the Mediterranean through the Bosporus, but the Bosporus is a natural canal cut through continental rock some 7,000 years ago, rather than a piece of oceanic sea floor like the Strait of Gibraltar.
Lack of clean water
Almost 50% of the developing world’s population; 2.5 billion people lacks improved sanitation facilities, and over 884 million people still use unsafe drinking water sources. Inadequate access to safe water and sanitation services, coupled with poor hygiene practices, kills and sickens thousands of children every day, and leads to impoverishment and diminished opportunities for thousands more.
Poor sanitation, water and hygiene have many other serious repercussions. Children – and particularly girls – are denied their right to education because their schools lack private and decent sanitation facilities. Women are forced to spend large parts of their day fetching water. Poor farmers and wage earners are less productive due to illness, health systems are overwhelmed and national economies suffer. Without WASH (water, sanitation and hygiene), sustainable development is impossible.
Source; UNICEF, July 2010
Facts about water
Today’s water crisis is not an issue of scarcity, but of access. More people in the world own cell phones than have access to a toilet. And as cities and slums grow at increasing rates, the situation worsens. Every day, lack of access to clean water and sanitation kills thousands, leaving others with reduced quality of life.
- 884 million people lack access to safe water supplies; approximately one in eight people.
- 3.575 million People die each year from water-related disease.
- The water and sanitation crisis claims more lives through disease than any war claims through guns.
- People living in the slums often pay 5-10 times more per liter of water than wealthy people living in the same city.
- An American taking a five-minute shower uses more water than a typical person in a developing country slum uses in a whole day.
- Only 62% of the world’s population has access to improved sanitation – defined as a sanitation facility that ensures hygienic separation of human excreta from human contact.
- Lack of sanitation is the world’s biggest cause of infection.
- 2.5 billion People lack access to improved sanitation, including 1.2 billion people who have no facilities at all.
- Of the 60 million people added to the world’s towns and cities every year, most occupy impoverished slums and shanty-towns with no sanitation facilities.
- Diarrhea remains in the second leading cause of death among children under five globally. Nearly one in five child deaths – about 1.5 million each year – is due to diarrhea. It kills more young children than AIDS, malaria and measles combined.
- Every 20 seconds, a child dies from a water-related disease.
- Diarrhea is more prevalent in the developing world due, in large part, to the lack of safe drinking water, sanitation and hygiene, as well as poorer overall health and nutritional status.
- Children in poor environments often carry 1,000 parasitic worms in their bodies at any time.
- In the developing world, 24,000 children under the age of five die every day from preventable causes like diarrhea contracted from unclean water.
- 1.4 million Children die as a result of diarrhea each year.
- In just one day, more than 200 million hours of women’s time is consumed for the most basic of human needs — collecting water for domestic use.
- This lost productivity is greater than the combined number of hours worked in a week by employees at Wal*Mart, United Parcel Service, McDonald’s, IBM, Target, and Kroger, according to Gary White, co-founder of Water.org.
- Millions of women and children spend several hours a day collecting water from distant, often polluted sources.
- A study by the International Water and Sanitation Centre (IRC) of community water and sanitation projects in 88 communities found that projects designed and run with the full participation of women are more sustainable and effective than those that do not. This supports an earlier World Bank study that found that women’s participation was strongly associated with water and sanitation project effectiveness.
- At any given time, half of the world’s hospital beds are occupied by patients suffering from diseases associated with lack of access to safe drinking water, inadequate sanitation and poor hygiene.
- The majority of the illness in the world is caused by fecal matter.
- Almost one-tenth of the global disease burden could be prevented by improving water supply, sanitation, hygiene and management of water resources. Such improvements reduce child mortality and improve health and nutritional status in a sustainable way.
- 88% of cases of diarrhea worldwide are attributable to unsafe water, inadequate sanitation or insufficient hygiene.
- 90% of all deaths caused by diarrheal diseases are children under 5 years of age, mostly in developing countries.
- It is estimated that improved sanitation facilities could reduce diarrhea-related deaths in young children by more than one-third. If hygiene promotion is added, such as teaching proper hand washing, deaths could be reduced by two thirds. It would also help accelerate economic and social development in countries where sanitation is a major cause of lost work and school days because of illness.
- Over 50 % of all water projects fail and less than five percent of projects are visited, and far less than one percent have any longer-term monitoring.
- Investment in safe drinking water and sanitation contributes to economic growth. For each $1 invested, the World Health Organization (WHO) estimates returns of $3 – $34, depending on the region and technology.
- Almost two in every three people who need safe drinking water survive on less than $2 a day and one in three on less than $1 a day.
- Households, not public agencies, often make the largest investment in basic sanitation, with the ratio of household to government investment typically 10 to 1.
- Investment in drinking-water and sanitation would result in 272 million more school attendance days a year. The value of deaths averted, based on discounted future earnings, would amount to US$ 3.6 billion a year.
- Less than 1% of the world’s fresh water (or about 0.007% of all water on earth) is readily accessible for direct human use.
- More than 80% of sewage in developing countries is discharged untreated, polluting rivers, lakes and coastal areas.
- The UN estimates that by 2025, forty-eight nations, with combined population of 2.8 billion, will face freshwater “stress” or “scarcity”. Our Water.org High School Curriculum
- Agriculture is the largest consumer of freshwater by far: about 70% of all freshwater withdrawals go to irrigated agriculture.
- At home the average American uses between 100 and 175 gallons of water a day. That is less than 25 years ago, but it does not include the amount of water used to feed and clothe us.
- Conserving water helps not only to preserve irreplaceable natural resources, but also to reduce the strain on urban wastewater management systems. Wastewater is costly to treat, and requires continuous investment to ensure that the water we return to our waterways is as clean as possible.