My Science School

CAVES

When rock is worn away by coastal erosion or rainwater, weak areas tend to collapse while the surrounding stronger rock survives. This creates cave systems, which may extend for many kilometres in limestone country, and contain huge caverns and underground rivers. Flowing water beneath glaciers can also erode caves in the ice. In places like Hawaii, erupting volcanoes may create lava tubes – tunnels that once contained rivers of red-hot molten rock.

LIMESTONE CAVES

Rainwater dissolves carbon dioxide from the air, turning it into weak carbonic acid. In limestone country, the acidified rainwater drains into the rock and dissolves it, creating chains of potholes and caverns. Where water containing dissolved rock drips from cave ceilings, it leaves stony deposits that build up into hanging stalactites, and stalagmites that grow up from the cave floor.

UNDERGROUND WATER

The water that creates limestone caves flows through the cave systems as underground streams and even rivers. In wet weather these can fill the caves, eroding them into fantastic shapes that are revealed as the water level drops. In some limestone regions, such as the Yucatan in Mexico, there is no surface water at all because all the rivers flow underground. In places they are open to the sky, forming beautiful natural wells called cenotes.

CRYSTALS

Water dripping through cave systems contains dissolved minerals, such as calcite and gypsum. If the water evaporates or changes its chemical nature slightly, the minerals may become solid again, forming crystals with glittering, faceted, jewel-like shapes.

COASTAL CAVE

On exposed rocky coasts, pounding waves force water into cracks in the rock at such high pressure that they blow the rock apart. This cuts away the rock at water level. Often the rock above collapses to form a sheer cliff, but if the waves cut into a weaker seam they can create deep caves and even rock arches.

GLACIER CAVE

Near the end of a glacier, melting ice creates streams of melt water that often drain down through crevasses to form vertical sinkholes. When the water reaches the bottom of the glacier, it flows between the ice and rock to erode tunnels and caves in the ancient glacier ice. At times when the melting rate is high these can fill with water, which pours through the ice in a torrent before finally emerging at the glacier tip or snout. In midwinter, however, these glacier caves may be safe to explore.

ICE CAVE

In some mountain regions, the air inside limestone caves can be so cold that water seeping into the cave immediately freezes. This creates glassy icicles and frozen cascades. The temperature is critical to the formation of these ice caves, so they are quite rare. If the rock around the cave is too cold, water freezes solid before it can enter the cave. If the cave is too warm, all the ice melts and the water drains away through the cave floor.

LAVA TUBE

Now cold and empty, this cave was once filled with a torrent of red-hot lava erupting from a Hawaiian volcano. The lava from such volcanoes is so hot and liquid that it flows like water. As it pours downhill, the top of the flow cools and may become solid, forming the roof of a lava tube. This keeps the heat in and allows the lava inside to keep flowing. When the eruption stops, the lava may flow out to leave a long cave.

CALCITE BARRIERS

Water flowing through the limestone cave of Akiyoshi-do in Japan is saturated with dissolved calcium carbonate, or calcite. Where the water flows over the sloping cave floor, calcite has crystallized to form a series of barriers. The water overflows these in a gentle cascade that falls from one pool to the next.

Picture Credit : Google

CLIMATE ZONES

Variations in the intensity of sunlight striking different parts of Earth drive global air movements and weather systems. Between them, these influences create a variety of climate zones, ranging from steamy tropical rainforests to the icy deserts of Antarctica. Most of these climate zones have a distinctive type of vegetation, which is the basis of a whole wildlife community, or biome.

• TROPICAL RAINFOREST

Intense sunshine near the Equator makes moisture evaporate and rise into the air to form huge storm clouds. These spill heavy, warm rain on the land below, fuelling the growth of dense rainforests.

• TEMPERATE FOREST

Temperate climates are neither very hot nor very cold. Near oceans, the mild, damp weather allows trees to grow well in summer, but many lose their leaves and stop growing in winter.

• POLAR AND TUNDRA

The Polar Regions get only weak sunlight in summer, and are dark all winter. They stay frozen all year, but in the north this icy region is surrounded by tundra, which thaws in summer allowing some plants to grow.

• MOUNTAIN

High mountain peaks are very cold, like Arctic tundra, and they have similar tough, low-growing vegetation. Lower mountain slopes are warmer, allowing trees to grow. The upper edge of this zone is called the tree line.

• DESERT

Some regions get so little rain that they are deserts. Many lie in a zone of hot, dry air near the tropics, but others are just too far from oceans. Some plants live in deserts, so they are not quite barren.

• MEDITERRANEAN

The dry shrublands that lie between the temperate zones and the main desert regions are named after the Mediterranean area where they are most common. The tough-leaved plants that live there can survive drying out in the hot summers.

• CLIMATE ZONES

The climate zones of the world form bands, with tropical rainforest near the Equator, most deserts in the subtropics, and boreal forest in the far north. Grasslands develop where it is too dry for trees.

• TROPICAL GRASSLAND

Tropical regions that are not within the zone of heavy rainfall are too hot and dry to support dense forest. They are seas of grass, often known as savannas, sometimes dotted with trees that can withstand long droughts.

• TEMPERATE GRASSLAND

Some temperate areas get little rainfall, usually because they lie at the hearts of great continents. Too dry for trees, they are naturally grassy steppes and prairies – although many are now farmland.

• BOREAL FOREST

To the south of the Arctic tundra, the northern continents support a band of dense forest. Most of the trees are conifers with stiff needle-like leaves that can survive the long, freezing winters.

Picture Credit : Google

WEATHER

Driven by the heat of the Sun, circulating currents of air swirl through the lower atmosphere, creating the winds that carry clouds, rain, and snow from the oceans over the land. Without these weather systems the continents would be barren deserts, where life would be impossible. Sometimes, however, the weather can be so violent that it causes destruction on a terrifying scale.

• PREDICTING WEATHER

Satellite images like this view of a hurricane in the Gulf of Mexico can help meteorologists predict the weather. Forecasters also gather data on wind, temperature, air pressure, and other variables, and feed them into computers that are programmed with Mathematical models of the atmosphere. The computers use the new data to predict how the atmosphere may react, and so produce a weather forecast.

• HURRICANES

The most devastating weather occurs over tropical oceans, where intense heat creates huge storm clouds that revolve around zones of very low air pressure. Winds spiral into the centre at 300 km/h (185 mph) or more, heaping ocean water into “storm surges” that can drown coastal cities. Hurricanes that form over the Pacific Ocean are called typhoons.

• ICE STORMS

Freezing winter weather is normal in many regions, but freak conditions can sometimes cause unusually destructive ice storms. If moist air is swept over a very cold region, falling rain may freeze where it lands to form thick ice. This can bring down power lines, paralyze rail networks, and turn roads into death traps.

• FLOODS

Heavy rain can swell rivers until they overflow their banks, flooding nearby low-lying land. The water may rise slowly, but it can also surge down valleys in sudden “flash floods” that sweep everything before them. Either way the flood water can wreck homes and even swamp cities.

• HAILSTONES

Big thunderclouds contain updrafts that carry raindrops to heights where they freeze. The pellets of ice fall through the cloud, but are carried up again so more ice freezes onto them. This can happen many times, building up hailstones that can be bigger than golf balls.

• THUNDERSTORMS

Hot sunshine causes water to evaporate and rise into the air, where it cools and forms clouds. Some clouds build up to immense heights of 15 km (9 miles) or more. They contain a huge weight of water that is eventually released in dramatic thunderstorms of torrential rain.

• TORNADOES

Thunderclouds are built up by rising warm, moist air that spirals up into the cloud. Sometimes this can develop into a tight, swirling vortex of rising air, called a tornado. Wind speeds inside the vortex can exceed 500 km/h (310 mph), and the powerful updraft can easily rip the roof off a house.

• LIGHTNING

Ice crystals tossed around inside a thundercloud can charge the cloud with electricity like a giant battery. Eventually the charge is released as a colossal spark of lightning, which heats the air along its path to about 30,000°C (50,000°F) in a split second.

ROCKS AND MINERALS

Rocks are mixtures of natural chemical compounds called minerals, which form crystals with distinctive shapes. There are three main types of rock. Igneous rock is formed when molten rock cools and hardens, a metamorphic rock is one that has been changed by heat or pressure, and sedimentary rock is generally made from fragments of rock cemented together.

1. Slate: This dark rock is created when sedimentary shale is put under intense pressure. It forms thin sheets that can be cut into squares and used for roofing.
2. Cockscomb barite: This whitish mineral is often found in veins running through rocks. Its crystals form clusters that can resemble cockscombs (roosters’ head crests).
3. Schist: Like slate, schist is created by pressure and heat, which transforms a soft sedimentary rock into a very much harder metamorphic rock.
4. Chalk: A type of limestone, chalk is built up from the remains of tiny marine organisms, which sank to the bottom of a tropical sea during the age of dinosaurs.
5. Marble: Hard and usually pale, marble is a metamorphic form of limestone. It can be carved and polished into statues, and decorative slabs are used in architecture.
6. Calcite: The main mineral in limestone and marble, calcite forms the stalactites and stalagmites seen in limestone caves.
7. Limestone: All limestones are made of chalky minerals, particularly calcite. They are easily dissolved by rainwater, creating extensive cave systems.
8. Halite: Formed by the evaporation of salt lakes, halite is rock salt - the mineral that we use to flavour our food.
9. Biotite: Dark brown biotite is a type of mica, a mineral found in most granites and schists. Its plate-like crystals resemble thin, flaky sheets of hard plastic.
10. Eclogite: A dense, heavy metamorphic rock formed deep beneath Earth’s surface, eclogite contains bright green pyroxene and glittering red garnet minerals.
11. Tremolite: Thin, transparent, fibrous-looking crystals of tremolite form from limestones that have been subjected to intense heat deep underground.
12. Beryl: This very hard mineral forms transparent, often greenish crystals that can be cut to create emeralds and aquamarines.
13. Granite: One of the main rocks that form continents, granite results from molten rock cooling slowly deep underground to form big quartz, feldspar, and mica crystals.
14. Breccia: This sedimentary rock is made of broken, sharp-edged rock fragments cemented together by finer particles.
15. Obsidian: Also known as volcanic glass, this shiny black or dark green rock is formed when molten lava cools too quickly to form crystals.
16. Gabbro: This is a coarse, dark, iron-rich, crystalline rock that makes up much of the deep ocean floor.
17. Pumice: Gas erupting from volcanoes often forms bubbles inside cooling lava. This can then form pumice, which has so many gas bubbles that it floats on water.
18. Corundum: This dull-looking stone is a type of corundum, the hardest mineral after diamond. Its crystals are used to make rubies and sapphires.
19. Albite: A pale, sodium-rich form of feldspar, albite is a common ingredient of granite, visible as big, blocky crystals that glint in the sunshine.
20. Graphite: Made of pure carbon – like diamond – graphite is a soft, metallic mineral that leaves a dark streak. It is used to make the “lead” in pencils.
21. Basalt: Heavy, dark basalt is the fine-grained form of gabbro, created when iron-rich lava from oceanic volcanoes cools quickly, often underwater.
22. Sandstone: Sand cemented together by other minerals forms sandstone. This red sandstone was once a desert dune.
23. Pyrite: Known as “fool’s gold”, this yellow metallic mineral is actually made of iron and sulfur. It often forms big cubic crystals like the ones seen here.
24. Conglomerate: Very like breccia, this rock is a solid, cemented mass of rounded pebbles, like those found on riverbeds and lake shores.

Picture Credit : Google

??TALS

Metals are minerals with a closely packed atomic structure, which makes them excellent conductors of electricity and heat. Most are also strong, workable materials, ideal for making a huge range of artefacts. Pure metals are elements, with only one type of atom in their chemical structure. In nature, many are mixed with rocks, or combined with other elements to form chemical compounds. These ores must be mined and processed to extract the pure metals.

LEAD

Very dense and heavy, lead is a dark, soft metal with a low melting point, which makes it easy to shape. It is widely used in lead-acid car batteries, but also for heavy weights and roofing. The main lead ore is galena, a compound of lead and sulfur that forms big crystals.

SILVER

One of the most prized metals, silver occurs in pure “native” form in volcanic rocks. It is very shiny when polished, but soon tarnishes. Since it is quite soft, it is often mixed with other metals to make harder alloys such as sterling silver.

PLATINUM

A beautiful, very heavy metal, platinum is often used in jewellery because, like gold, it never tarnishes. It is tougher than gold, and rarer, so it is more precious. It is sometimes found as nuggets of pure metal.

GOLD

Easily worked, always shiny, and the only metal that is always found in pure form, gold has been used to make precious objects for thousands of years. It is also used to make electrical contacts that do not degrade by tarnishing.

COPPER

Copper is a soft metal, often alloyed with zinc to make brass, or with tin to form bronze – both much harder. A good conductor, it is widely used for electric wire. Its main ore is chalcopyrite, a compound of copper, iron, and sulfur.

TITANIUM

Light yet very strong, titanium is often combined with other metals to make lightweight alloys used in aircraft, spacecraft, and the pressure - proof capsules of deep-sea submersibles. One of its main ores is rutile, a compound of titanium and oxygen.

ALUMINIUM

Abundant and resistant to corrosion, lightweight aluminium is widely used for foil, cans, and in aircraft. Its ore, bauxite, is a rock that contains many aluminium compounds.

NICKEL

Rarely used on its own, nickel is often alloyed with iron to make stainless steel. This is used for all kinds of applications, from knives and forks to replacement hip joints. Nickel is also alloyed with silver to make coins.

MERCURY

The only metal that is liquid at room temperature, mercury is most familiar as the silvery contents of a medical thermometer. Its ore, cinnabar, is a colourful compound of mercury and sulfur found near volcanoes.

IRON

The most useful of all metals, iron is strong, abundant, and easy to work with, especially when refined into various types of steel. Its main ore is hematite, an iron oxide – the same thing as rust.

ZINC

Zinc is a white metal that is alloyed with copper to make brass. Its main use, however, is plating or “galvanizing” steel to make it rust- proof. Its main ore is sphalerite, a sparkling mineral that is a compound of zinc, iron, and sulfur.

TIN

Well known for its use in tin cans – which are actually tin-plated steel – tin is widely used in electronic components because of its high electrical conductivity. It is also alloyed with lead to make the solder used to assemble electronic circuits.

Picture Credit : Google

EARTHQUAKES

The vast rocky plates of Earth’s crust are always moving. Where the plates meet, the movement causes earthquakes. Frequent slight movement just causes tremors (shaking), but often the rocks on each side of a plate boundary lock together. The strain builds up, distorting the rocks until the locked section gives way. The Rock Springs back, often shifting several metres and the shock of this can cause a catastrophic earthquake.

CHILE 1960

The biggest earthquake ever recorded struck Chile in 1960. It reached 9.5 on the Richter scale, which was devised in 1935 by American scientist Charles Richter as a way of measuring earthquakes using instruments called seismographs.

ALASKA 1964

On 27 March 1964, the Pacific Ocean floor slid 20 m (66 ft) beneath Alaska in a few minutes, causing a colossal earthquake. So few people live in this remote region, however, that only 125 lost their lives.

SAN FRANCISCO 1906

The San Andreas Fault in California, USA, marks where the Pacific plate is sliding past North America. San Francisco is built on the fault line, and in 1906 the city was almost destroyed when the fault slipped 6 m (20 ft) and triggered disastrous fires.

MEXICO CITY 1985

Mexico’s capital city is built on the dried-out clay bed of an ancient lake. The earthquake that hit the city in 1985 made the clay shakes like jelly, making the shock waves six times as destructive. More than 400 multistorey buildings in the city were shaken to the ground, and at least 9,000 people died.

???? 1995

Japan was created by intense earth movements in the western Pacific, and it has more earthquakes than almost anywhere else. In 1995, an earthquake wrecked the city of Kobe, destroying this elevated highway and killing 6,433 people.

TSUNAMI 2004

The Asian tsunami that killed more than 283,000 in 2004 was caused by an earthquake on the ocean floor off Sumatra. The shock sent huge waves racing across the Indian Ocean, devastating communities all around its shores. The city of Banda Aceh, Sumatra, Indonesia, as it was in April 2004

INDONESIA 2006

In 2006, a serious earthquake struck the Indonesian island of Java, wrecking up to 135,000 houses and killing at least 5,780 people. It also damaged the ancient Hindu temple of Prambanan, a World Heritage Site, but did not destroy it.

Picture Credit : Google

MOUNTAINS

The world’s mountains were raised by the titanic forces that keep the plates of Earth’s crust moving. Where the plates grind together, the edges of continents are forced up into high, folded ridges, like the Andes Mountains in South America. Hot rock deep beneath the surface may erupt through cracks in the folded rock to form volcanoes. These also erupt where the crust is being torn apart, and over “hotspots” deep within Earth. The landscape below has been created from images of the highest peaks on each continent, and one that rises from the depths of the Pacific Ocean.

• MOUNT EVEREST

The world’s highest peak, Everest lies 8,850 m (29,035 ft) above sea level. It is part of the Himalayas, a range of Fold Mountains created by the collision of India with Asia

50 million years ago. India is still moving north, so the Himalayas are still rising.

• MOUNT ACONCAGUA

The Pacific Ocean floor is plunging beneath South America, rucking up its western edge to form the rugged, earthquake-prone mountains of the Andes. Mount Aconcagua is the highest peak, at 6,959 m (22,834 ft).

• MOUNT MCKINLEY

Rising 6,194 m (20,321 ft) above sea level, Mount McKinley in Alaska is the highest peak of the North American Western Cordillera. Its isolation and bulk make it one of the world’s most spectacular mountains.

• MOUNT KILIMANJARO

The highest mountain in Africa, Kilimanjaro is actually a colossal volcano with three volcanic cones. The highest peak on the tallest cone, Kibo, rises 5,895 m (19,340 ft) above sea level. The other volcanic cones are Mawenzi and Shira.

• MAUNA KEA

The highest point on Hawaii is the top of a huge volcano that rises 10,000 m (33,000 ft) from the Pacific Ocean floor. So although its peak is only 4,205 m (13,796 feet) above sea level, it is the biggest mountain on Earth.

• VINSON MASSIF

The most remote mountains on Earth lie on the frozen continent of Antarctica. Overlooking the vast mass of the Ronne Ice Shelf, Vinson Massif in the Ellsworth range is the highest point at 4,897 m (16,067 ft).

• MONT BLANC

The folded ridges of the European Alps have been raised by the northward movement of Africa. Mont Blanc is the highest peak at 4,808 m (15,774 ft), but since its summit is a dome of ice its height varies from year to year.

• AORAKI (MOUNT COOK)

The highest peak in New Zealand, Aoraki’s name means “cloud piercer” in the native Maori language. The mountain is also known as Mount Cook. Now 2,744 m (12,284 ft) high, Aoraki was 10 m (33 ft) higher before a landslide in 1991.

Picture Credit : Google

OCEANS

The oceans cover more than two-thirds of the surface of Earth, with an average depth of 3.8 km (2.4 miles), but they are not just huge pools of salt water. The ocean floors are where the great plates of Earth’s crust are splitting apart or grinding together, creating long, high ridges and deep trenches dotted with volcanoes. As a result of this, the oceans are changing their size and shape all the time.

PACIFIC ??EAN

As big as all other oceans put together, the Pacific is shrinking as the edges of its floor slip into deep ocean trenches like the Mariana Trench. The East Pacific Rise, however, is the most active mid-ocean ridge, spreading at up to 22 cm (8.5 in) a year.

ATLANTIC OCEAN

The Atlantic formed when North and South America split from Europe and Africa and gradually moved west. The ocean is still growing as new ocean floor is created at the Mid-Atlantic Ridge. The ridge breaks the surface in the north to form Iceland, with its volcanoes and geysers.

ARCTIC OCEAN

Most of the Arctic Ocean is covered by thick floating ice in winter. A lot of this melts in spring, allowing sunlight to reach the cold waters and fuel the growth of ocean life. The sea near the North Pole stays frozen in summer, but the area covered by ice is shrinking every year because of global warming.

INDIAN OCEAN

This mainly tropical ocean is notorious for the tsunami that swept across it from Sumatra in 2004. It had a serious impact on nearby coasts and low-lying coral islands like the Maldives, which crown the peaks of an underwater mountain ridge extending south from India.

SOUTHERN OCEAN

With no obvious northern boundaries, the Southern Ocean forms a ring of cold, stormy water around Antarctica. Ice covers a vast area in winter, and the giant icebergs that break off Antarctic glaciers and ice shelves sometimes drift well north.

Picture Credit : Google

VOLCANOES

Volcanoes are the most spectacular and destructive of Earth’s geological features. Most volcanoes lie along plate boundaries, where the slabs of rock (plates) that form Earth’s crust meet. Opening rifts and the friction of plates grinding against each other make the hot rock beneath the crust melt and burst up through fissures (cracks). Volcanoes also occur over “hotspots” away from plate boundaries, caused by rising plumes of heat in the mantle beneath Earth’s crust.

KILAUEA

The Hawaiian Islands are a chain of volcanoes that have erupted from the Pacific Ocean floor as it slips over a hotspot in Earth’s mantle. The oldest volcanoes in the north are now extinct, but Kilauea in the south is the most active volcano on Earth.

• ERUPTION

When Kilauea erupts, basalt lava and gas are forced up from deep within the volcano. Basalt lava is very fluid, so a lot of it just spills over the rim of the crater. Erupting gas can also cause explosive “fire fountains” of gas and red-hot lava, like this one.

• CRATER

Lava boils up through a vent to build up a cone of rocky debris. More eruptions make the inside of the cone collapse or even explode upwards to create a roughly circular crater. It’s almost sheer walls reveal layers of cinders, ash, and solidified lava.

• CONE

This small volcanic cone is just the summit of a huge, dome-shaped shield volcano, which rises all the way from the ocean floor 7,277 m (23,875 ft) below. The dome is built up by the fluid lava that erupts on Hawaii. Volcanoes that erupt stickier, less fluid lava have steeper sides.

• LAVA FLOW

The lava that erupts from Kilauea is extremely hot, and is so fluid that it flows downhill away from the crater like a river of fire. Since 1983 the volcano has been erupting almost constantly, spilling lava over more than 100 sq km (40 sq miles).

• TYPES OF LAVA

Hawaiian lava is molten basalt rock pushed up from beneath the ocean floor. It is fluid because it contains very little silica (the mineral used to make glass). Other volcanoes erupt lava that is high in silica, which is much stickier and does not flow far.

• LAVA TUBE

As the lava streams away from the active crater of Kilauea, the surface of the flow cools and hardens. Underneath, however, the hot lava keeps flowing. This creates “lava tubes” that extend to the coast, where the lava spills into the sea in clouds of steam.

Picture Credit : Google

 

PLANET EARTH

Earth was created some 4.5 billion years ago from a mass of iron-rich, rocky debris orbiting the Sun. The rocks smashed into the young planet as meteorites, and were welded together by heat generated from the energy of impact. The bombardment eventually generated so much heat that the whole planet melted. The heavy iron then sank towards the centre to become Earth’s core, while the lighter rocks formed the mantle and crust.

EARTH’S STRUCTURE

The planet is layered like a peach. Earth’s rocky crust forms its thin skin, while the hot, mobile rock of the mantle is like the peach’s juicy flesh. At the heart of the planet lies its metallic core, like the hard stone at the centre of a peach.

ON THE SURFACE

Movement in the thick, hot mantle has made the thin, cool crust crack into several huge plates. The boundaries of these plates are marked by earthquake zones dotted with volcanoes, and mountain ridges pushed up where moving plates collide.

• INNER CORE

The inner core is a heavy ball of solid iron and nickel. It is heated by nuclear reactions within Earth to 4,700°C (8,500°F), but the intense pressure at the core prevents it from melting.

• OUTER CORE

The solid inner core is surrounded by a fluid mass of molten iron, nickel, and sulfur. Swirling currents in the molten metal of the outer core generate Earth’s magnetic field.

• LOWER MANTLE

The rocky mantle is 2,900 km (1,800 miles) deep, and is heated to 3,500°C (6,300°F) at its base. Intense pressure stops it melting, but rising heat keeps the hot rock moving slowly.

• UPPER MANTLE

The upper mantle is heated to almost 1,000°C (1,800°F). Where movement in the mantle cracks the cool, brittle crust, reduced pressure makes the hot mantle rock melt and erupt from volcanoes.

• OCEANIC CRUST

The crust between the continents is less than 11 km (7 miles) thick. It is, made of heavy rock that erupts from the hot mantle at mid-ocean ridges to form the bedrock of the ocean floors.

• CONTINENTAL CRUST

The lightest of Earth’s rocks form vast slabs that “float” on the heavy mantle like huge rocky rafts. Up to 70 km (45 miles) thick, they rise above sea level to form the continents we live on.

• LAND SURFACE

Exposed to frost, wind, rain, and hot sunlight, the rocks at the land surface are broken down by weathering and erosion. This releases minerals that are vital to plants and other life.

• OCEANS

The low-lying basins between the continents are filled with water, to an average depth of 3.7 km (2.3 miles). Most of the water erupted from volcanoes as water vapour early in Earth’s history.

• WEATHER SYSTEMS

The heat of the Sun makes water evaporate from the oceans and rise into the lower atmosphere. The water forms swirling masses of cloud that spill rain onto the continents, allowing life to exist on land.

• ATMOSPHERE

Earth’s mass gives it enough gravity to retain an atmosphere of nitrogen, oxygen, and other gases including carbon dioxide. This keeps Earth warm at night, and shields it from dangerous radiation.

THE MOON

Soon after Earth formed, it was hit by a planet-sized asteroid that completely disintegrated. Most of its heavy metallic core melted into Earth, but the lighter rocky fragments drifted into orbit and eventually fused to form the Moon.

Picture Credit : Google

PLATE TECTONICS

Earth’s crust is the brittle shell of a deep layer of hot rock called the mantle. This is moving very slowly, driven by heat generated deep within the planet. The movement has made the crust crack into separate plates, which are being pulled apart in some places and pushed together in others. As they move, the plates make oceans larger or smaller, and carry continents around the globe.

PLATE BOUNDARIES

At some plate boundaries the plates are pulling apart, while at others they are pushing together. There are also places where one plate is sliding against another. All these movements cause earthquakes, and many boundaries are dotted with volcanoes.

Convergent boundaries

These are found where one plate grinds beneath another. Ocean floors always slide under continents, pushing up mountain ranges.

Divergent boundaries These occur where plates are pulling apart, usually on ocean floors. This allows hot mantle rock to erupt in the rift zone and solidify as new ocean floor.

KIT OF PARTS

There are 15 large tectonic plates, and almost 40 smaller ones. They form the ocean floors, and some of the largest carry continents. Continental plates are made of thicker, but lighter, rock than the ocean floors. The oceanic parts of the plates are always changing size and shape, but the continents, although moving, do not change so much.

FRACTURED GLOBE

The plates fit together to form the globe. Some plates are moving apart at divergent boundaries, but the world never gets bigger because the fringes of other plates are being destroyed at convergent boundaries. The relative movement of the Pacific, Cocos and Caribbean plates shows how the plate boundaries are formed.

Picture Credit : Google

SPACE TRAVELLERS

Since the first manned space mission in 1961, more than 560 people have journeyed into space - 27 on missions to the Moon and the rest in orbit around Earth. To date, only Russia, China, and the United States have launched humans into space. However, humans are not the only space travellers. Animals such as dogs, monkeys, and spiders have all been sent into space to help with research.

1. Alan Shepard was the second person, and first American, to journey into space.
2. Ulf Merbold, from Germany, became the first European to fly aboard a space shuttle.
3. Jim Voss set the record for longest spacewalk (8 hours 56 minutes) with Susan Helms.
4. Susan Helms.
5. Laika was the first animal to orbit Earth. The Russian dog travelled in Sputnik 2 in 1957.
6. Alexei Leonov made the first spacewalk in March 1965. He spent 10 minutes in space secured to his Voskhod 2 craft.
7. Eileen Collins became the first female shuttle pilot in February 1995, and the first female shuttle commander in July 1999.
8. Yang Liwei was the first Chinese astronaut (taikonaut). China’s first manned space flight was launched in October 2003.
9. Svetlana Savitskaya was the second woman in space and the first woman to spacewalk.
10. Michael Collins was the third member of the Apollo 11 mission in 1969. He orbited the Moon, as Armstrong and Aldrin explored its surface.
11. Dennis Tito was the first space tourist. He paid £14 million ($20 million) for a six-day trip in 2001.
12. Baker, a squirrel monkey, was launched into space on 28 May 1959. She travelled with a rhesus monkey called Able.
13. Eugene Cernan was part of the Apollo 17 mission in December 1972. He was the last person to walk on the Moon.
14. Neil Armstrong was the first person to set foot on the Moon. He spent 2 hours 35 minutes exploring the lunar surface.
15. Yuri Gagarin was the first person to fly into space. His trip in April 1961 took him once round Earth and lasted 108 minutes.
16. Peggy Whitson holds the record for the longest female spaceflight (289.2 days).
17. Mike Melvill was the first commercial astronaut. He piloted SpaceShipOne in June 2004.
18. Valentina Tereshkova was the first woman to fly into space. She made a three-day journey aboard Vostok 6 in June 1963.
19. Gennady Padalka holds the record for the total time spent in space. In his five trips, he has clocked up 878.5 days in space.
20. Sam was a rhesus monkey who was sent into space in 1960 to test equipment that would be used in future manned flights.
21. Valeri Polyakov holds the record for the longest time spent in space during one trip. His record stands at 437.7 days.
22. Bruce McCandless made the first untethered spacewalk in February 1984.
23. John Glenn was the first American to orbit Earth, in 1962. He became the oldest space voyager in 1998, aged 77.
24. Green tree frogs were taken to the Mir space station in 1990.
25. Buzz Aldrin was the second person to set foot on the Moon.
26. Swordtail fish travelled on board the space shuttle Columbia in 1998.
27. Squirrel monkeys and 24 albino rats were taken to Spacelab-3 in 1985.
28. Arabella, a spider, was sent to the Skylab space station in 1973. Once space-adapted, she spun perfect webs.
29. Albino rats.
30. Quail chicks hatched from eggs on the Mir space station in March 1990.
31. Belka and Strelka became the first dogs to go into orbit and survive the journey in 1960.
32. Ham was the first chimpanzee to travel in space. In 1961, he was sent to test equipment that would be used in the first US manned space mission.

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TELESCOPES

A telescope is the astronomer’s basic tool. It makes distant objects appear bigger and reveals their detail. Telescopes work by using a lens or mirror to collect light and bring it to a focus, producing an image. Reflectors, which use a mirror, are the most widely used type of telescope - the bigger the mirror, the more powerful the telescope and the better the view.

• NAKED-EYE VIEW The constellation of Orion is easily visible to the naked eye. On a dark, moonless night, a faint, fuzzy patch of light may be visible below the three stars of Orion’s belt. This is the Orion Nebula.
• THROUGH BINOCULARS The Orion Nebula is a massive star-forming cloud of gas and dust. The nebula becomes more obvious when looked at through binoculars — two low-powered telescopes working together. In standard binoculars the two main lenses are about 5 cm (2 in) wide and the image is magnified seven times.
• IMPROVED VIEW A more powerful telescope improves the view of the nebula. Across the world there are about 50 telescopes with mirrors 2-5 m (6.5-16.5 ft) across and another 20 with mirrors up to 10 m (33 ft) across. These large telescopes are located on mountain-top sites where the air is clear and still. Computerized controls adjust their position, keeping them tracked on their target as Earth turns.
• MEDIUM-SIZED TELESCOPE VIEW The nebula’s shape and form become visible through a telescope with a mirror about 20 cm (7.8 in) across. A camera attached to the telescope collects the light and records the image.
• X-RAY AND INFRARED VIEWS X-rays collected by the Chandra space telescope were used to make this image on the left, which shows the heart of the Orion Nebula. The image on the right shows the same area taken by the Spitzer infrared telescope. Clouds of dust heated by starlight show up in red.
• VIEW FROM SPACE Some telescopes collect forms of energy other than light, such as radio waves, X-rays, and infrared energy. Earth’s atmosphere prevents some of these from reaching Earth so they are collected by telescopes in space. This colour-enhanced image combines data from two space telescopes - Spitzer, which collects infrared waves, and Hubble, which collects both light and ultraviolet waves.
• HEART OF THE NEBULA Hubble’s 2.4-m (7.9-ft) wide mirror collected the light for this detailed view of the Orion Nebula’s bright central area. It includes the Trapezium, a cluster of ten young, brilliant stars that illuminate the nebula with their ultraviolet energy.

Picture Credit : Google

 

SPACE EXPLORATION

Humans have only been able to send spacecraft to explore space for about 50 years. In that time, more than 100 robotic craft have travelled into the Solar System to reveal what its planets, moons, asteroids, and comets are like. They fly by, orbit, or land on these other worlds. Humans have only been to the Moon, but aim to set foot on Mars in the future.

TIMELINE OF SPACE EXPLORATION

14 October 1957: Sputnik 1, the world’s first artificial satellite, is launched into Earth’s orbit by Russia.

3 November 1957: Laika, a Russian dog aboard Sputnik 2, becomes the first creature to orbit Earth.

2 January 1959: Russian spacecraft Luna 1 is the first to escape Earth’s gravity.

13 September 1959: Luna 2 is the first craft to land on the Moon when it crashes onto its surface.

12 April 1961: Russian Yuri Gagarin is the first person into space. His flight lasts 108 minutes.

16 June 1963: Russian Valentina Tereshkova is the first woman in space.

18 March 1965: Russian Alexei Leonov makes the first EVA (extra vehicular activity), or spacewalk.

3 February 1966: Luna 9 lands successfully on the Moon.

24 December 1968: US spacecraft Apollo 8 is the first manned mission to leave Earth’s gravity and orbit the Moon.

20 July 1969: Neil Armstrong and Buzz Aldrin of Apollo 11 are the first humans to walk on the Moon.

19 April 1971: The first space station, Salyut 1, is launched by the Russians.

3 December 1973 US craft Pioneer 10 is the first to fly by Jupiter.

29 March 1974: US craft Mariner 10 is the first to fly by Mercury.

17 July 1975: US craft Apollo 18 and Russian Soyuz 19 make the first international space rendezvous.

22 October 1975: Russian craft Venera 9 transmits the first images from the surface of Venus.

20 July 1976: US craft Viking 1 is the first to land successfully on Mars.

1 September 1979: Pioneer 11 is the first to fly by Saturn.

12 April 1981: Columbia, the first US space shuttle, is launched.

24 January 1986: US craft Voyager 2 is the first to fly by Uranus.

13 March 1986: European craft Giotto takes the first close-up look at a comet.

24 August 1989: Voyager 2 is the first craft to fly by Neptune.

24 April 1990: The Hubble Space Telescope is launched.

15 September 1990: US craft Magellan starts a three-year mapping programme of Venus.

29 October 1991: US craft Galileo makes the first flyby of an asteroid as it passes Gaspra. 13 July 1995: Galileo arrives at Jupiter and releases a probe to enter its atmosphere.

4 July 1997: US craft Mars Pathfinder and its Sojourner rover touch down on Mars.

20 November 1998: Zarya, the first module of the International Space Station (ISS), is launched.

2 November 2000: The first crew arrives to stay aboard the ISS.

12 February 2001: The NEAR craft lands on asteroid Eros.

25 December 2003: Europe’s first interplanetary craft, Mars Express, orbits Mars.

30 June 2004: US craft Cassini arrives at Saturn to study the planet and its moons. It releases Huygens to land on the moon Titan.

20 November 2005: Japanese craft Hayabusa lands on asteroid Itokawa.

4 August 2007: US craft Phoenix sets off for Mars, arriving in 2008.

18 March 2011: US Messenger spacecraft becomes the first vehicle to orbit around Mercury.

6 August 2012: US Curiosity rover lands in the Gale Crater on Mars.

6 August 2014: European spacecraft Rosetta, carrying the Lander Philae, enters orbit around Comet Churyumov-Gerasimenko.

14 July 2015: US craft New Horizons makes the first flyby of the dwarf planet Pluto.

5 July 2016: US Juno spacecraft enters orbit around Jupiter to survey the planet’s Polar Regions.

15 September 2017: Cassini ends its mission with a deliberate plunge into Saturn’s atmosphere.

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METEORITES

Thousands of tonnes of rocky material enter Earth’s atmosphere each year. Most of it originates from asteroids, but some comes from comets, the Moon, and even Mars. As the rocky pieces close in on Earth they are termed meteoroids. Most burn up, but those that survive and land are known as meteorites. There are three main types: stony meteorites, iron meteorites, and stony-iron meteorites - the rarest kind.

• ESQUEL This stony-iron meteorite was collected in Esquel, Argentina, in 1951. Golden-coloured crystals of the mineral olivine are embedded in the iron-nickel metal.
• THIEL The Thiel Mountains stony-iron meteorite was one of the first found in Antarctica, in 1962.
• METEOR Meteoroids burning up in Earth’s atmosphere produce bright trails. These short-lived streaks of light are termed meteors, or shooting stars. About a million occur every day.
• MURCHISON Stony meteorites are the most common. This one, the Murchison, fell in Australia in 1969. It is one of the most studied meteorites and contains minerals, water and complex organic molecules.
• BARWELL The Barwell meteorite is one of a shower of stones that fell in England in 1965. As it plummeted through Earth’s atmosphere, friction caused the outer surface to heat and melt. This later solidified into a black crust.
• CANON DIABLO This sliced and polished iron meteorite is a piece of the asteroid that produced the Barringer Crater. The pieces found weigh 30 tonnes in total, yet they are only a small fraction of the original asteroid.
• IMPACT CRATER Meteorites can produce craters when they crash into Earth. The Barringer Crater in the Arizona Desert, USA, shown here under a rare blanket of snow, measures 1.2 km (0.75 miles) across and was formed about 50,000 years ago.
• GIBEON Iron meteorites are the second most common type, after stony meteorites. The Gibeon is mainly iron with a small amount of nickel. It is one of many found in Namibia since the 1830s.
• CALCALONG CREEK More than 50 meteorites found on Earth originated on the Moon, blasted off by asteroid impact. The Calcalong creek meteorite, found in Australia, is lunar surface soil that was turned to rock by such an impact.
• NAKHLA This stony meteorite is one of more than 30 found on Earth that originated on Mars. It was blasted off the planet and spent many millions of years in space before landing in Egypt on 28 June 1911.
• TEKTITES Small glassy bodies known as tektites can form when a large meteorite hits Earth. The impact shatters and melts surrounding Earth rock, flinging it upwards. It cools and hardens, falling back to Earth as glassy pieces.

Picture Credit : Google