My Science School

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

Mercury is the Roman god of commerce, communication, travel, and thievery. Venus is the god of love and beauty in Roman mythology. Mars gets its name from the Roman god of War. Jupiter, meanwhile, is the King of Gods in Roman mythology, making the name of a fitting choice for the largest planet in our solar system. Saturn, the farthest planet that can be seen by the unaided human eye, gets its name from the Roman god of wealth and agriculture. Uranus is named after the ancient Greek deity of the skies and the heavens. Neptune, the farthest planet from the sun, is named after the Roman god of the Sea.

No Greco-Roman connect

In case you read the above paragraph, and read it again to see if you had missed out Earth in it, you can be assured that Earth isn’t mentioned in it. This is because Earth is the only planet in the solar system whose English name does not derive from Roman or Greek mythology.

The English name of the planet, Earth, comes from Old English and Germanic. It is derived from the Old English words eor(th)e, ertha, and eorpe, all of which correspond to both “ground, soil, dirt, country” and “the abode of man, the material world”. The Proto-Germanic words erde and erp-o also have similar meanings.

Common theme

While this much is known, there is no clear answer as to how exactly Earth got this name. The planet we call home, however, has many other names in many other languages. Despite the vast amount of languages spoken in the world and their very different histories, the name used for Earth in most languages is a form of a word that is connected to ‘ground’ or ‘soil’. What is Earth called in your native language?

 

Picture Credit : Google

Earth’s magnetic field behaves like a giant bar magnet with north and south poles. Many mechanisms have been postulated to explain how the magnetic field is generated, but the only one that is widely accepted is analogues to a dynamo. That is, Earth’s magnetic field is caused by a dynamo effect.

The mechanism is similar to that of the working of a dynamo start spinning when the bicycle is pedaled, creating an electric current. The electricity, thus created, keeps the light on. Magnetic fields occur whenever electric charge is in motion. If there is a rotating electric current, it will create a magnetic field.

The Earth’s magnetic field has its source in the flow of molten iron in its outer core. Electric current is generated due to the motion of convection currents of molten iron. The rotation of Earth on its axis causes these electric currents to form a magnetic field which extends around the planet.

 

Picture Credit : Google