7th Graders - Life Science - it's alot like Biology!!
Since sunlight illuminates only the upper layers, the major part of the ocean exists in permanent darkness. The Gods of the Greeks. As waves approach land and move into shallow water , they change their behavior. From the 16th to the 19th centuries, about 13 million people were shipped across the Atlantic to be sold as slaves in the Americas. Regions of North America.
Several tsunamis can be caused by a single geological event. In such cases, it is common for the later waves to arrive between eight minutes and two hours after the first, which may not be the biggest or most destructive.
Tides are the regular rise and fall in water level experienced by seas and oceans in response to the gravitational influences of the Moon and the Sun, and the effects of the Earth's rotation.
At any given place, the water rises over the course of the tidal cycle to a maximum height known as "high tide" before ebbing away again to a minimum "low tide" level.
As the water recedes, it uncovers more and more of the foreshore or intertidal zone. The difference in height between the high tide and low tide is known as the tidal range or tidal amplitude. Most places experience two high tides each day, occurring at intervals of about 12 hours and 25 minutes, half the period that it takes for the Earth to make a complete revolution and return the Moon to its previous position relative to an observer. The Moon's mass is some 27 million times smaller than the Sun, but it is times closer to the Earth.
On the opposite side of the Earth, the lunar force is at its weakest and this causes another bulge to form. These bulges rotate around the Earth as the moon does. The Sun's effect is less powerful but, when the Sun, Moon and Earth are all aligned at the full and new moons , the combined effect results in the high "spring tides". Tidal flows of seawater are resisted by the water's inertia and can be affected by land masses.
In places like the Gulf of Mexico where land constrains the movement of the bulges, only one set of tides may occur each day. Inshore from an island, there may be a complex daily cycle with four high tides. The island straits at Chalkis on Euboea experience strong currents which abruptly switch direction, generally four times per day but up to 12 times per day when the moon and the sun are 90 degrees apart.
Although tides are regular and predictable, the height of high tides can be lowered by offshore winds and raised by onshore winds. The high pressure at the center of an anticyclones pushes down on the water and is associated with abnormally low tides while low-pressure areas may cause extremely high tides.
Wind blowing over the surface of the sea causes friction at the interface between air and sea. Not only does this cause waves to form but it also makes the surface seawater move in the same direction as the wind. Although winds are variable, in any one place they predominantly blow from a single direction and thus a surface current can be formed.
Westerly winds are most frequent in the mid-latitudes while easterlies dominate the tropics. There are five main gyres in the world's oceans: These gyres have followed the same routes for millennia, guided by the topography of the land, the wind direction, and the Coriolis effect.
The surface currents flow in a clockwise direction in the Northern Hemisphere and anticlockwise in the Southern Hemisphere. The water moving away from the equator is warm, while that flowing towards it has lost most of its heat.
These currents tend to moderate the Earth's climate, cooling the equatorial region, and warming regions at higher latitudes. Surface currents only affect the top few hundred meters yards of the sea, but there are also large-scale flows in the ocean depths caused by the movement of deep water masses.
A main deep ocean current flows through all the world's oceans and is known as the thermohaline circulation or global conveyor belt. This movement is slow and is driven by differences in density of the water caused by variations in salinity and temperature.
Both these factors make it denser and the water sinks. From the deep sea near Greenland, such water flows southwards between the continental landmasses on either side of the Atlantic. When it reaches the Antarctic, it is joined by further masses of cold, sinking water and flows eastwards. It then splits into two streams that move northwards into the Indian and Pacific Oceans. Here it is gradually warmed, becomes less dense, rises towards the surface, and loops back on itself.
Some flows back into the Atlantic. It takes a thousand years for this circulation pattern to be completed. Besides gyres, there are temporary surface currents that occur under specific conditions.
When waves meet a shore at an angle, a longshore current is created as water is pushed along parallel to the coastline. The water swirls up onto the beach at right angles to the approaching waves but drains away straight down the slope under the effect of gravity. The larger the breaking waves, the longer the beach, and the more oblique the wave's approach, the stronger the longshore current is.
It may occur at a gap in a sandbar or near a man-made structure such as a groyne. This cold water is often rich in nutrients and creates blooms of phytoplankton and a great increase in the productivity of the sea. Bathymetry is the mapping and study of the topography of the ocean floor. Methods used for measuring the depth of the sea include single or multibeam echosounders , laser airborne depth sounders and the calculation of depths from satellite remote sensing data. This information is used for determining the routes of undersea cables and pipelines, for choosing suitable locations for siting oil rigs and offshore wind turbines and for identifying possible new fisheries.
The crust below land is known as continental while that under the abyssal sea is called oceanic. The latter is composed of relatively dense basalt and is some five to ten kilometers three to six miles thick. The relatively thin lithosphere floats on the weaker and hotter mantle below and is fractured into a number of tectonic plates. Parallel to these ridges and nearer the coasts, one oceanic plate may slide beneath another oceanic plate in a process known as subduction.
Deep trenches are formed here and the process is accompanied by friction as the plates grind together. The movement proceeds in jerks which cause earthquakes. Heat is also produced and magma is forced up, creating underwater mountains, some of which grow into volcanic islands. Near some boundaries between the land and sea, the slightly denser oceanic plates slide beneath the continental plates and more subduction trenches are formed.
As they grate together, the continental plates are deformed and buckle causing mountain building and seismic activity.
It is near the Mariana Islands , a volcanic archipelago in the West Pacific. It occurs where the oceanic Nazca Plate slides under the continental South American Plate and is associated with the upthrust and volcanic activity of the Andes.
The zone where land meets sea is known as the coast and the part between the lowest spring tides and the upper limit reached by splashing waves is the shore. A beach is the accumulation of sand or shingle on the shore. The indentation of a coastline—especially between two headlands—is a bay ; a small bay with a narrow inlet is a cove and a large bay or bay-shaped sea may be referred to as a gulf.
Normally, waves roll towards the shore at the rate of six to eight per minute. These are known as constructive waves as they tend to move material up the beach and have little erosive effect. Storm waves arrive on shore in rapid succession and are known as destructive waves , as their swash moves beach material seawards.
Under their influence, the sand and shingle on the beach is ground together and abraded. Around high tide, the power of a storm wave impacting on the foot of a cliff has a shattering effect as air in cracks and crevices is compressed and then expands rapidly with release of pressure.
At the same time, sand and pebbles have an erosive effect as they are thrown against the rocks. Along with other weathering processes such as frost, this tends to undercut the cliff. Gradually, a wave-cut platform develops at the foot of the cliff and this has a protective effect, reducing further wave-erosion. Material worn from the margins of the land eventually ends up in the sea, where it is subject to attrition as currents flowing parallel to the coast scour out channels and transport material away from its place of origin.
Sediment carried to the sea by rivers settles on the seabed causing deltas to form in estuaries. All these materials move back and forth under the influence of waves, tides, and currents. Governments make efforts to prevent flooding through building breakwaters , seawalls , and other defenses against the sea.
In Britain, the Thames Barrier protects London from storm surges,  while the failure of the dykes and levees around New Orleans during Hurricane Katrina created a humanitarian crisis in the United States. Land reclamation in Hong Kong permitted the construction of Hong Kong International Airport through the leveling and expansion of two smaller islands. Following the adoption of the present UNCLOS , the coastline under international law is a state 's baseline , which is generally but not always equivalent to its low-water line.
Over most of geologic time, the sea level has been higher than it is today. For at least the last years, the sea level has been rising at an average rate of about 1.
Additional contributions, as much as one quarter of the total, come from water sources on land, such as melting snow and glaciers and extraction of groundwater for irrigation and other agricultural and human needs. The sea plays a part in the water cycle , in which water evaporates from the ocean, travels through the atmosphere as vapor , condenses , falls usually as rain or snow again, and then largely returns to the sea.
These endorheic basins , particularly in central Asia , sometimes build up permanent salt lakes as inflowing waters evaporate and their dissolved minerals accumulate over time. The largest of these is the Caspian Sea , although it is sometimes counted as a proper sea owing to its basin of now-landlocked oceanic crust.
Oceans contain the greatest quantity of actively-cycled carbon in the world and are second only to the lithosphere in the amount of carbon they store. The deep layer's concentration of dissolved inorganic carbon is about 15 percent higher than that of the surface layer  and it remains there for much longer periods of time.
Carbon enters the ocean as atmospheric carbon dioxide dissolves into the surface layers and is converted into carbonic acid , carbonate , and bicarbonate: It can also enter as dissolved organic carbon through rivers and is converted by photosynthetic organisms into organic carbon. This can either be exchanged throughout the food chain or precipitated into the deeper, more carbon-rich layers as dead soft tissue or in shells and bones as calcium carbonate.
It circulates in this layer for long periods of time before either being deposited as sediment or being returned to surface waters through thermohaline circulation.
Seawater is slightly alkaline and had a preindustrial pH of about 8. One important element for the formation of skeletal material in marine animals is calcium , but calcium carbonate becomes more soluble with pressure, so carbonate shells and skeletons dissolve below its compensation depth.
Affected planktonic organisms will include the snail-like molluscs known as pteropods , and single-celled algae called coccolithophorids and foraminifera. All of these are important parts of the food chain and a diminution in their numbers will have significant consequences. In tropical regions, corals are likely to be severely affected as it becomes more difficult to build their calcium carbonate skeletons,  in turn adversely impacting other reef dwellers.
The current rate of ocean chemistry change appears to be without precedent in Earth's geological history, making it unclear how well marine ecosystems will be able to adapt to the shifting conditions of the near future.
The oceans are home to a diverse collection of life forms that use it as a habitat. Since sunlight illuminates only the upper layers, the major part of the ocean exists in permanent darkness. As the different depth and temperature zones each provide habitat for a unique set of species, the marine environment as a whole encompasses an immense diversity of life. Life may have originated in the sea and all the major groups of animals are represented there.
Scientists differ as to precisely where in the sea life arose: Marine habitats can be divided horizontally into coastal and open ocean habitats.
Coastal habitats extend from the shoreline to the edge of the continental shelf. Most marine life is found in coastal habitats, even though the shelf area occupies only 7 percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of the continental shelf.
Alternatively, marine habitats can be divided vertically into pelagic open water , demersal just above the seabed , and benthic sea bottom habitats. A third division is by latitude: Coral reefs, the so-called "rainforests of the sea", occupy less than 0. Marine primary producers —plants and microscopic organisms in the plankton—are widespread and very diverse.
Microscopic photosynthetic algae, phytoplankton, contribute a larger proportion of the world's photosynthetic output than all the terrestrial forests combined. About 45 percent of the sea's primary production of living material is contributed by diatoms.
The marine nitrogen cycle consists of complex microbial transformations which include the fixation of nitrogen , its assimilation, nitrification , anammox , and denitrification. This means that the most productive areas, rich in plankton and therefore also in fish, are mainly coastal.
There is a broader spectrum of higher animal taxa in the sea than on land, many marine species have yet to be discovered, and the number known to science is expanding annually. In fact, the oceans teem with life and provide many varying microhabitats.
The pelagic zone contains macro - and microfauna and myriad zooplankton which drift with the currents. Most of the smallest organisms are the larvae of fish and marine invertebrates which liberate eggs in vast numbers because the chance of any one embryo surviving to maturity is so minute. The demersal zone supports many animals that feed on benthic organisms or seek protection from predators.
The seabed provides a range of habitats on or under the surface of the substrate which are used by creatures adapted to these conditions. The tidal zone with its periodic exposure to dehydrating air is home to barnacles , molluscs , and crustaceans. The neritic zone has many organisms that need light to flourish. Here, sponges , echinoderms , polychaete worms , sea anemones , and other invertebrates live among algal-encrusted rocks.
Corals often contain photosynthetic symbionts and live in shallow waters where light penetrates. The extensive calcareous skeletons they extrude build up into coral reefs which are an important feature of the seabed.
These provide a diverse habitat for reef dwelling organisms. There is less sea life on the floor of deeper seas but marine life also flourishes around seamounts that rise from the depths, where fish and other animals congregate to spawn and feed.
Close to the seabed live demersal fish that largely feed on pelagic organisms or benthic invertebrates. Some like the detritivores rely on organic material falling to the ocean floor. Others cluster round deep-sea hydrothermal vents where mineral-rich flows of water emerge, supporting communities whose primary producers are sulphide-oxidizing chemoautotrophic bacteria and whose consumers include specialized bivalves, sea anemones, barnacles, crabs, worms, and fish.
Such places support unique biomes where many new microbes and other lifeforms have been discovered. Humans have travelled the sea since prehistoric times , originally on rafts and in dugout , reed , and bark canoes. Most of the early human migrations occurred over land: The hunter-gatherer Ortoiroid people began spreading through the Caribbean from Venezuela 's Orinoco valley by at least the 6th millennium BC. Around the same time, Mesopotamians were using bitumen to caulk their reed boats and, a little later, masted sails.
Herodotus records Egyptian claims that he also commissioned a 3-year-long expedition which circumnavigated Africa from the Red Sea to the Nile delta. A modified form was used by Columbus for his voyages. The first evidence of its use in Chinese maritime navigation, however, dates to Zhu Yu 's c. Alexander of Neckham 's De naturis rerum , the first European mention of a magnetized needle, dates to and immediately notes its use among sailors.
Accurately determining longitude the ship's position east or west of some fixed point proved much harder. In the 15th century, West European mariners—beginning with Portugal —started making still longer voyages of exploration , using improvements on translated Islamic star charts and a variation on African fishing boats called the caravel. In , Lopes Gonçalves crossed the equator and disproved the Aristotelian notion that a ring of fire would bar exploration of the southern hemisphere.
Bartolomeu Dias rounded the Cape of Good Hope in ; in , Vasco da Gama reached Malindi , where a local pilot showed him how to follow the monsoon to India. In , relying on incorrect estimates of the circumference of the Earth , the Genovese Christopher Columbus sailed from Cadiz to the Canaries and thence into the open Atlantic in a Spanish attempt to reach the Orient.
Instead, he made landfall on an island in the Caribbean Sea. The resulting Columbian Exchange introduced potatoes , corn , and chili peppers to the Old World while smallpox epidemics devastated the indigenous peoples of the Americas. This disruption and depopulation permitted rapid Spanish conquests and led to the widespread adoption of African slavery to man lucrative tobacco, sugar, indigo, and cotton plantations. In , Gerardus Mercator devised a map projection conveniently making constant bearings rhumb lines straight.
Although accurate charting of the coasts of Russia only began in the 18th century and the archipelago of Severnaya Zemlya was not discovered until ,  Novgorodians had been sailing the White Sea since at least the 13th century. In the early 15th century, Zheng He 's fleet of treasure ships repeatedly sailed from Ming China with 37, men aboard ships, reaching as far as the African coast. The peoples of East Asia were introduced to the true shape of the other continents from the maps of Matteo Ricci.
Meanwhile, the determination of longitude continued to involve approximations and guesswork: Great Britain 's Longitude prize was effectively awarded in to the self-educated John Harrison for his sea watch of James Cook used a copy of this on his second and third voyages, which studied the Pacific  and inspired studies from Russia , France , the Netherlands, and the United States.
Earlier ideas that no life could exist below fathoms meters or 1, feet were disproved in when a Mediterranean line failed and was pulled up from depths four times lower, completely encrusted with marine life. During the mids, Fridtjof Nansen used a specially-designed ship to drift through the northern pack ice , establishing that the Arctic was an open sea. From , the International Hydrographic Organization in Monaco has standardized surveying and charting of the sea  and, from , the Discovery Investigations studied whales and mapped the seas around Antarctica.
The Cold War and oil exploration funded further deep sea research: Today, the American Global Positioning System GPS enables accurate navigation worldwide using over thirty satellites and message timing so exact as to involve general relativity. Water-borne trade has been practiced since at least the dawn of civilization , when Sumeria was connected to Harappan India. In the first centuries BC, steppe nomads' interruption of India's access to Siberian gold caused them to open up maritime routes to Malaysia and Indonesia,  exposing them first to Hindu and then Muslim traders.
With the collapse of the Roman Empire, European trade dwindled but it continued to flourish elsewhere. Following further conquests , Arabians came to dominate maritime trade in the Indian Ocean , spreading Islam along the East African coast and, eventually, Southeast Asia.
From the 16th to the 19th centuries, about 13 million people were shipped across the Atlantic to be sold as slaves in the Americas. Nowadays, large quantities of goods are transported by sea, especially across the Atlantic and around the Pacific Rim. A major trade route passes through the Pillars of Hercules , across the Mediterranean and the Suez Canal to the Indian Ocean and through the Straits of Malacca ; much trade also passes through the English Channel.
Over 60 percent of the world's container traffic is conveyed on the top twenty trade routes. There are two main kinds of freight, bulk cargo and break bulk or general cargo, most of which is now transported in containers. Commodities in the form of liquids, powder or particles are carried loose in the holds of bulk carriers and include oil, grain, coal, ore, scrap metal, sand and gravel.
Break bulk cargo is usually manufactured goods and is transported in packages, often stacked on pallets. Before the arrival of containerization in the s, these goods were loaded, transported and unloaded piecemeal. Its objectives include developing and maintaining a regulatory framework for shipping, maritime safety, environmental concerns, legal matters, technical co-operation and maritime security. Spearfishing with barbed harpoons along the sea coast was widespread by the Palaeolithic.
Improvements in sonar during the world wars were adapted as fishfinders and, during the s, great factory ships caught and processed as many fish in an hour as earlier trawlers had in a season. As of , there were an estimated At present, the species most frequently landed are herring , cod , anchovy , tuna , flounder , mullet , squid, and salmon. A number of these, as well as large predatory fish,  remain well below historical levels.
Over 3 million vessels are employed in sea fishing. The equipment used to capture the fish may be purse seines , other seine , trawls , dredges, gillnets , and long-lines. The Food and Agriculture Organization of the United Nations is encouraging the development of local fisheries to provide food security to coastal communities and help alleviate poverty.
As well as the wild stock, about 79 million metric tons 87 million tons of food and non-food products were produced by sea farming in , an all-time high. About six hundred species of plants and animals were cultured, some for use in seeding wild populations.
The animals raised included finfish , aquatic reptiles , crustaceans, molluscs, sea cucumbers , sea urchins , sea squirts, and jellyfish. Various methods are employed. Mesh enclosures for finfish can be suspended in the open seas, cages can be used in more sheltered waters, or ponds can be refreshed with water at each high tide. Shrimps can be reared in shallow ponds connected to the open sea. Oysters can be reared on trays or in mesh tubes.
Sea cucumbers can be ranched on the seabed. In the s, disease wiped out China's farmed Farrer's scallop and white shrimp and required their replacement by other species. Admiralty law is the particular body of national laws applied to maritime questions and offenses, as the uncertainty of sea voyages has caused the sea to be viewed as a unique jurisdiction since antiquity. Rhodian , Roman , Byzantine , Trani , and Amalfian laws were important influences on the French , Genovese , and Hanseatic codes which established the first English courts of admiralty.
Unlike the usual English common law system, the courts of admiralty hewed closer to Continental practice , leaving it open for abuse that contributed to the American Revolution. The Law of the Sea is the particular body international law applied to maritime questions and offenses.
Empires such as Rome and China long claimed universal jurisdiction ; during the Middle Ages , Italian maritime republics such as Venice and Genoa recognized the existence of rival states but claimed the right to close the seas to their traffic. Truman 's unilateral claim of jurisdiction over the oil reserves of America's continental shelf in  directly led to the end of the regime. The "internal waters" landward of the baseline are solely under national control.
A "contiguous zone" of a further 12 nmi are permitted for hot pursuit of vessels charged with violating customs, taxation, immigration, or pollution laws in the territorial waters. Ships may cross numerous time zones on a voyage, so nautical time , introduced in the s, is used in international waters.
Each such zone is uniformly 15 degrees of longitude wide, the ship's clock going forward one hour per zone when travelling eastwards.
Since the development of coordinated fleets of ships capable of landing an invasion force, naval warfare has been an important aspect in the defense or conquest of maritime states. The BC Battle of Salamis largely determined the course of the Persian Wars  not because of its inherent damage however considerable but because Themistocles 's deception and superior strategy left the Athenians capable of disrupting sea-borne supplies at will and potentially striking at the pontoon bridges across the Hellespont , cutting off the Persians' line of retreat.
Piracy —both illicit in ancient Cilicia and China and state-supported among the Cretans , Vikings , Japanese , English , and Berbers  —has remained a problem into the present day , given the expense involved in securely protecting every merchant vessel or in policing extensive coastlines. In the ancient world, in addition to Salamis , major naval engagements included the Battle of Actium , which permitted the establishment of Augustus 's empire. In the modern era, important naval battles include the English victories against the Armada in and at Trafalgar in ,  which broke the threats of invasion by the superior land forces of the Spanish and French empires.
With steam, mass-produced steel plate, and exploding shells, European gunships permitted the New Imperialism of the 19th century, forcing open access to Africa , China , Korea , and Japan for their merchants on favorable terms.
Although internal politics hampered Chinese modernization, American naval power produced a major reform in Japan which bore fruit during the Battle of Tsushima when the Japanese were able to decisively defeat Russia. Meanwhile, the battles of the Mediterranean  and Pacific   theaters of the war had shown that air power was capable of overcoming the strongest warships. Although the use of small private vessels for personal transport undoubtably extends back into prehistory, large ships capable of braving the open ocean were typically dedicated to trade or fishing for most of human history.
Even military campaigns would often simply hire or commandeer these private fleets to serve as troop transports , as did the traders, pilgrims , and wealthy tourists of antiquity and the Middle Ages. The voyages of exploration and colonization were often provided for by the crown out of naval funds; where they were not, they were usually chartered or else purchased and then used for shipping supplies after the initial settlement. Dedicated and scheduled local passenger services came to be offered in the 16th and 17th centuries, but the Black Ball was the first trans-Atlantic passenger line.
In the Age of Sail , the duration of such passages depended much on the prevailing winds and the weather. The 18th-century coastal Margate hoys began the popularization of leisure travel in Britain and Ireland  that later gathered steam with Thomas Cook 's package tours in the next century. By , the Atlantic crossing took about five days and the passenger lines competed to win the Blue Riband , an unofficial accolade accorded to the fastest liner in regular service.
For twenty years from , the prize went to the RMS Mauretania for its average speed of The sea still remains a venue for recreational boating and large cruise ships.
It is also a route for refugees and economic migrants , some traveling in small unseaworthy craft and others smuggled into shipping vessels. Some flee persecution while many are economic migrants attempting to reach countries where they believe their prospects are brighter. Use of the sea for leisure developed in the nineteenth century and became a significant industry in the twentieth century. Many humans enjoy venturing into the sea: This was not always the case, with sea bathing becoming the vogue in Europe in the 18th century after Dr.
William Buchan advocated the practice for health reasons. Other water sports include kite surfing , where a power kite propels a manned board across the water;  windsurfing , where the power is provided by a fixed, maneuverable sail;  and water skiing , where a powerboat is used to pull a skier.
Beneath the surface, freediving is necessarily restricted to shallow descents. Other useful equipment includes fins and snorkels. Scuba equipment allows underwater breathing, permitting hours of time beneath the surface. Deeper dives can be made with specialized equipment and training. The sea offers a very large supply of energy carried by ocean waves , tides , salinity differences, and ocean temperature differences which can be harnessed to generate electricity.
Tidal power uses generators to produce electricity from tidal flows, sometimes by using a dam to store and then release seawater.
The Rance barrage , 1 kilometer 0. The large and highly variable energy of waves gives them enormous destructive capability, making affordable and reliable wave machines problematic to develop. It was soon damaged by waves, then destroyed by a storm. Offshore wind power is captured by wind turbines placed out at sea; it has the advantage that wind speeds are higher than on land, though wind farms are more costly to construct offshore.
Electricity power stations are often located on the coast or beside an estuary so that the sea can be used as a heat sink. A colder heat sink enables more efficient power generation, which is important for expensive nuclear power plants in particular.
There are large deposits of petroleum as oil and natural gas in rocks beneath the seabed. Offshore platforms and drilling rigs extract the oil or gas and store it for transport to land.
Offshore oil and gas production can be difficult due to the remote, harsh environment. Animals may be disorientated by seismic waves used to locate deposits, probably causing the beaching of whales. The infrastructure may cause damage and oil may be spilt. The sea holds enormous quantities of valuable dissolved minerals.
Bromine , accumulated after being leached from the land, is economically recovered from the Dead Sea, where it occurs at 55, parts per million ppm. This has advantages over land-based mining in that equipment can be built at specialized shipyards and infrastructure costs are lower. Disadvantages include problems caused by waves and tides, the tendency for excavations to silt up, and the washing away of spoil heaps. There is a risk of coastal erosion and environmental damage.
They form when geothermally superheated water is emitted from deep sea hydrothermal vents known as " black smokers ": The ores are of high quality but currently very costly to extract. Desalination is the technique of removing salts from seawater to leave fresh water suitable for drinking or irrigation. The two main processing methods, vacuum distillation and reverse osmosis , use large quantities of energy.
Desalination is normally only undertaken where fresh water from other sources is in short supply or energy is plentiful, as in the excess heat generated by power stations. The brine produced as a by-product contains some toxic materials and is returned to the sea.
Some estimates put the amount available at between one and 5 million cubic kilometers 0. In the Pacific these may cover up to 30 percent of the deep ocean floor.
The minerals precipitate from seawater and grow very slowly. Their commercial extraction for nickel was investigated in the s but abandoned in favour of more convenient sources. In deeper waters, mobile seafloor crawlers are used and the deposits are pumped to a vessel above. In Namibia , more diamonds are now collected from marine sources than by conventional methods on land. Many substances enter the sea as a result of human activities. Combustion products are transported in the air and deposited through precipitation.
Agricultural, industrial, and sewage outflows contribute heavy metals , pesticides , PCBs , disinfectants , cleaning products, and other synthetic chemicals. These become concentrated in the surface film and in marine sediment, especially estuarine mud. The result of all this contamination is largely unknown because of the large number of substances involved and the lack of information on their biological effects.
They are then passed up the food chain. Run-off of fertilizers from agricultural land is a major source of pollution in some areas and the discharge of raw sewage has a similar effect. The extra nutrients provided by these sources can cause excessive plant growth. Nitrogen is often the limiting factor in marine systems and the addition of nitrogen sparks algal blooms and red tides , which then may lower the oxygen level of the water to the point where it kills marine animals.
Such events have created dead zones in the Baltic Sea and the Gulf of Mexico. The Irish Sea was contaminated by radioactive caesium from the former Sellafield nuclear fuel processing plant  and nuclear accidents sometimes cause radioactive material to seep into the sea, as at Fukushima in Also includes booklet covers for stations and a rubric for grading.
Includes 19 files below. Measuring Solids - Students use centimeters and inches to measure various solids. Identifying Solids - Students cut and label solids from magazines. Reading about Solids - Students record facts, examples, and questions about solids during reading. Weighing Solids - Students use a balance scale to weigh solids with two different units of measure.
Researching Solids - Students research solids using a website and record new information learned. Sorting Solids - Students draw and write how they sorted solids according to their properties. Counting Solids - Students understand that solids can be counted as they tally and record the number of certain solids in the classroom. Solids Presentation - Students create a storyboard for a PowerPoint slide to show what they've learned about solids.
Measuring Liquids - Students use teaspoons and tablespoons to measure various liquids. Identifying Liquids - Students cut and label liquids from magazines. Reading about Liquids - Students record facts, examples, and questions about liquids during reading. Weighing Liquids - Students use a balance scale to weigh lliquids with two different units of measure.
Researching Liquids - Students research liquids using a website and record new information learned. Sorting Liquids - Students draw and write how they sorted liquids according to their properties. Pouring Liquids - Students understand that liquids can be poured as they time the number of seconds it takes to pour various liquids. Liquids Presentation - Students create a storyboard for a PowerPoint slide to show what they've learned about liquids.
A rubric for grading students' participation and work in solid and liquid stations. Students choose 3 activities from this tic-tac-toe grid to practice matter concepts.
Students move around the room to identify types of matter in this game. Great to review for the test! Students move around the room to identify types of simple machines in this game. Students write and illustrate a story about how to use simple machines to lift a zoo animal into its cage! An entire unit filled with magnet experiments, writing activities, and assessment. Includes 11 files below. A cover to create student portfolios of magnet activities and journal writings.
Portfolio Activity 1 - Students explore the classroom to find out what magnets will stick to. Portfolio Activity 2 - Students explore various objects to determine the kinds of objects magnets will attract. Portfolio Activity 4 - Students explore the poles of magnets to learn about attract and repel. Portfolio Activity 5 - Students use paperclips to explore the strength of different parts of a magnet. Portfolio Activity 6 - Students make magnetic patterns with various shaped magnets and filings.
Journal writing pages for Portfolio Activities that requires students to use key words from the lessons. A scoring guide for grading Portfolio Activities and Journal writings. An entire unit filled with plant experiments, writing activities, minibooks, and data collection. Includes 14 files below. Students draw, label, and use construction paper flaps to learn about the 4 basic needs of a plant.
Animals, Wind, or Water? Students play a board game to practice identifying different stages of growth. Students move around the room to identify plant parts in this game. Students will create a weather calendar to keep track of daily weather for a month.
Cloudy With A Chance of Students will use their own snacks to illustrate a picture of a food storm. This page will be used to create a story problem about the food that rained down. Students choose 3 activities from this tic-tac-toe grid to practice weather concepts.
A five-day weather calendar for recording precipitation, cloud cover, cloud types, wind and temperature. Students move around the room to identify seasons in this game. Students create a sign to tell about the dangers of severe weather and tips of how to stay safe. Students try to get players to guess the weather term listed at the top of the card by giving clues without using the "forbidden" words listed on the card in this game. Signs with real photographs of weather tools - thermometer, wind sock, wind vane, anemometer, and rain gauge.
A sign for each food group that names the group, shows examples, and defines the group's benefit. Two sets of 43 food cards and directions for a relay game. Cards may also be used for classifying foods. Students create a book about the food groups. Includes cover page and one page for each food group. Students create a balanced meal in this activity. Students move around the room to identify food groups in this game. Includes 8 different game boards and 24 calling cards.
An assessment of students' understanding of the 5 food groups and why they are important. Students choose 3 activities from this tic-tac-toe grid to practice nutrition concepts. This Jeopardy-style PowerPoint game reviews food group categories. Students draw a pizza and write about what happens to the pizza as you eat it at a pizza joint. Students identify food groups in this game. Includes 32 gamecards and directions. A dictionary of 7 important teeth terms for students to alphabetize and illustrate.
Students write a story about what they think the tooth fairy does with all of the teeth she collects. Includes planning page, primary-lined writing page and intermediate-lined writing page.
Math - Students create a graph and answer questions about the number of teeth their classmates have lost. An entire unit filled with activities to learn about freshwater and salt water habitats. A PowerPoint to teach that the ocean is a habitat containing sand, minerals, plants, and animals. Includes a quiz at the end. Students complete a page for a class book by drawing how a fish sounds it will look and how it really looks. Students record similarities and differences between freshwater and salt water habitats on this chart.
A PowerPoint to teach the differences between freshwater and salt water and the animals that depend on each type of water. Students assemble a minibook about the characteristics of fish. Learning center includes a cover, 18 freshwater and salt water plant and animal cards, sorting mat, answer key, and directions. Students move around the room to identify water habitats in this game. An entire unit filled with activities to learn about rocks! Includes 10 activities below.
A slideshow to introduce three types of rocks: Students will sort rocks using these sorting cards color, size, shape, texture, weight, hardness. Students will test rocks for calcium carbonate and document the results on this recording sheet.