Category The World Around us

     The magnetic field of the Earth at any given time is preserved in the magnetic minerals within rocks that solidified during that period. Geologists are thus able to study the magnetic field of rocks thousands of years old, such as those used to build the pyramids at Giza, Egypt.

     A magnetic field is the area around a material in which its magnetic forces can be detected. Those forces stem from the activity of tiny, negatively charged particles called electrons, which are within all atoms. A material’s magnetism is determined by the way its electrons move around the outside of its atoms’ nuclei — particularly those electrons that aren’t paired with other electrons in certain ways. If a large number of unpaired electrons rotate in the same direction (imagine a large number of tops spinning on a table or other flat surface), then an object’s magnetic field can be strong. If all of the unpaired electrons spin in random directions, the object’s magnetic field is either very weak or missing.

     Some materials, such as lodestones, create a persistent magnetic field. Others with unpaired electrons, such as iron, can become magnetized when they’re placed within a magnetic field and their atoms rotate and align.

     Scientists don’t know how some types of rocks, including lodestones, become so strongly magnetized. But new lab tests show how some other rocks can become naturally magnetized.

     Charles Aubourg is a geologist at the University of Pau and the Adour Countries in France. He and his colleagues heated samples of a type of sedimentary rock to as much as 130 degrees Celsius (about 266 degrees Fahrenheit). Sedimentary rock is made from material eroded from other rocks. The eroded materials transform into stone when exposed to high pressure deep within Earth for a lengthy period of time, sometimes millions of years.

     Aubourg’s team got its rock samples from northern France, but similar rocks can be found worldwide. Each sample contained large amounts of clay and silt (both of which are made of tiny particles eroded from other rocks). But importantly, the rocks also contained a small amount of an iron-bearing mineral called pyrite.

     First, the team used a strong magnetic field to erase any magnetism naturally trapped in the sample. Then the researchers heated the rock inside a strong magnetic field according to a specific recipe: 25 days at 50 degrees Celsius, then 25 days at 70 degrees, 25 days at 80 degrees, 10 days at 120 degrees, and a final 10 days at 130 degrees. This temperature range is the same as that of rocks located between 2 kilometers and 4 kilometers deep in Earth’s crust, explains Aubourg.

     The rocks’ magnetic field rose during each stage of heating. It increased most quickly during the earliest days of each step. The growing magnetism of the samples suggests that the heat triggered reactions that caused some of the pyrite to chemically transform into magnetic minerals.

     Analyses conducted after the heating suggest that the magnetic minerals were very tiny grains of magnetite. These grains were so small, less than 20 nanometers across, that it would take more than 1,000 of them side by side to stretch across the width of a single human hair. The researchers reported their results online August 10 in the scientific journal Geochemistry, Geophysics, Geosystems.

     Because the grains of magnetite were so small, looking for one “would be like trying to find a needle in a haystack,” says Douglas Elmore. He is a sedimentary geologist at the University of Oklahoma in Norman. Nevertheless, he notes, the evidence is convincing that the heating experiments created small grains of magnetite, not other types of magnetic minerals.

     Studies that investigated rocks in their natural environment have hinted that rocks buried in shallow layers of Earth’s crust and heated there naturally can become magnetized, says Elmore. The new lab tests provide even stronger evidence that such magnetization occurs naturally, he adds.

     Studying the magnetic field trapped in ancient rocks helps scientists better understand Earth’s history, including how the planet’s magnetic field has changed through time.

Picture Credit : Google

    The earth is rather like an enormous magnet. Otherwise known as the magnetosphere, the Earth’s magnetic field stretches out into space, helping to protect the Earth from the Sun’s radiation. The magnetic poles are close to the geographic North and South Poles.

    A magnetic field is a vector field that describes the magnetic influence of electric charges in relative motion and magnetized materials. The effects of magnetic fields are commonly seen in permanent magnets, which pull on magnetic materials (such as iron) and attract or repel other magnets. Magnetic fields surround and are created by magnetized material and by moving electric charges (electric currents) such as those used in electromagnets. They exert forces on nearby moving electrical charges and torques on nearby magnets. In addition, a magnetic field that varies with location exerts a force on magnetic materials. Both the strength and direction of a magnetic field vary with location. As such, it is described mathematically as a vector field.

    In electromagnetics, the term “magnetic field” is used for two distinct but closely related fields denoted by the symbols B and H. In the International System of Units, H, magnetic field strength, is measured in the SI base units of ampere per meter. B, magnetic flux density, is measured in tesla (in SI base units: kilogram per second2 per ampere), which is equivalent to newton per meter per ampere. H and B differ in how they account for magnetization. In a vacuum, B and H are the same aside from units; but in a magnetized material, B/{\displaystyle \mu _{0}}  and H differ by the magnetization M of the material at that point in the material.

    Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. Magnetic fields and electric fields are interrelated, and are both components of the electromagnetic force, one of the four fundamental forces of nature.

    Magnetic fields are widely used throughout modern technology, particularly in electrical engineering and electromechanics. Rotating magnetic fields are used in both electric motors and generators. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits. Magnetic forces give information about the charge carriers in a material through the Hall Effect. The Earth produces its own magnetic field, which shields the Earth’s ozone layer from the solar wind and is important in navigation using a compass.

Picture Credit : Google

The molten iron that partly makes tip the Earth’s core continually flows around. As this happens, it generates powerful electric currents that create the Earth’s magnetic field. This is similar to the way magnetic currents are generated by an electric motor.

Earth’s magnetic field, also known as the geomagnetic field, is the magnetic field that extends from the Earth’s interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field is generated by electric currents due to the motion of convection currents of molten iron in the Earth’s outer core: these convection currents are caused by heat escaping from the core, a natural process called a geodynamo. The magnitude of the Earth’s magnetic field at its surface ranges from 25 to 65 microteslas (0.25 to 0.65 gauss). As an approximation, it is represented by a field of a magnetic dipole currently tilted at an angle of about 11 degrees with respect to Earth’s rotational axis, as if there were an enormous bar magnet placed at that angle through the center of the Earth. The North geomagnetic pole, which was in 2015 located on Ellesmere Island, Nunavut, Canada, in the northern hemisphere, is actually the south pole of the Earth’s magnetic field, and conversely.

While the North and South magnetic poles are usually located near the geographic poles, they slowly and continuously move over geological time scales, but sufficiently slowly for ordinary compasses to remain useful for navigation. However, at irregular intervals averaging several hundred thousand years, the Earth’s field reverses and the North and South Magnetic Poles respectively, abruptly switch places. These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in the past. Such information in turn is helpful in studying the motions of continents and ocean floors in the process of plate tectonics.

The magnetosphere is the region above the ionosphere that is defined by the extent of the Earth’s magnetic field in space. It extends several tens of thousands of kilometers into space, protecting the Earth from the charged particles of the solar wind and cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects the Earth from harmful ultraviolet radiation.

The Earth’s magnetic field serves to deflect most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation. One stripping mechanism is for gas to be caught in bubbles of magnetic field, which are ripped off by solar winds. Calculations of the loss of carbon dioxide from the atmosphere of Mars, resulting from scavenging of ions by the solar wind, indicate that the dissipation of the magnetic field of Mars caused a near total loss of its atmosphere.

The study of the past magnetic field of the Earth is known as paleomagnetism. The polarity of the Earth’s magnetic field is recorded in igneous rocks, and reversals of the field are thus detectable as “stripes” centered on mid-ocean ridges where the sea floor is spreading, while the stability of the geomagnetic poles between reversals has allowed paleomagnetists to track the past motion of continents. Reversals also provide the basis for magnetostratigraphy, a way of dating rocks and sediments. The field also magnetizes the crust, and magnetic anomalies can be used to search for deposits of metal ores.

Humans have used compasses for direction finding since the 11th century A.D. and for navigation since the 12th century. Although the magnetic declination does shift with time, this wandering is slow enough that a simple compass can remain useful for navigation. Using magnetoreception various other organisms, ranging from some types of bacteria to pigeons, use the Earth’s magnetic field for orientation and navigation.

Picture Credit : Google

         In 1990, a geological exploration began to find out more about the Earth’s crust. A hole drilled into the ground in the Kola Peninsula, Russia, has reached a depth of around 15km (9.3 miles). Nobody has been down it, and it is still well short of the Earth’s centre.

         Travelling to the Earth’s center is a popular theme in science fiction. Some subterranean fiction involves traveling to the Earth’s center and finding either a Hollow Earth or Earth’s molten core. Planetary scientist David J. Stevenson suggested sending a probe to the core as a thought experiment. Humans have drilled over 12 kilometers (7.67 miles) in the Sakhalin-I. In terms of depth below the surface, the Kola Superdeep Borehole SG-3 retains the world record at 12,262 metres (40,230 ft) in 1989 and still is the deepest artificial point on Earth.

         The idea of a so-called “Hollow Earth”, once popular in fantasy adventure literature, is that the planet Earth has a hollow interior and an inner surface habitable by human beings. Although the scientific community has made clear that this is pseudoscience, the idea nevertheless is a less popular feature of many fantasy and science fiction stories and of some conspiracy theories.

         The most famous example of a hollow-Earth fantasy is Jules Verne’s 1864 science-fiction novel Journey to the Center of the Earth, which has been adapted many times as a feature film and for television.

         The 2003 film The Core, loosely based on the novel Core, tells the story of a team that has to drill to the center of the Earth and detonate a series of nuclear explosions in order to restart the rotation of Earth’s core. The drilling equipment, dubbed Virgil, includes a powerful, snake-like laser drill, a small nuclear reactor for power, a shell (of “unobtainium”, a fictional material) to protect against intense heat and pressure (and generate energy to drive the engine), a powerful x-ray camera for viewing outside, and a system of impellers for movement and control. The only part of the Earth that turns out to be hollow is a gigantic geode, and soon after the drill moves through it, the hole it created fills with magma.

          The 1986 animated television show Inhumanoids featured regular visits to the Inner Core in most of its 13 episodes. Each of the three villainous creatures theoretically ruled over certain layers of the inner Earth, and their evil schemes were thwarted by the human Earth Corps, who often allied with various races of subterranean beings equally threatened by the Inhumanoids.

          During season 3 of the Teenage Mutant Ninja Turtles cartoon the Technodrome is located at the Earth’s core, and transport modules are used to drill up to the streets. This season also features the episode “Turtles at the Earth’s Core”, where a dinosaur lives in a deep cave, and a crystal of energy that works like the Sun to keep the dinosaurs alive. As Krang, Shredder, Bebop and Rocksteady steal the crystal to power the Technodrome, the trouble begins.

          Don Rosa’s 1995 Uncle Scrooge story The Universal Solvent imagines a way to travel to the planet’s core using 1950s technology, although this would be impossible in reality. The fictional solvent referred to in the story’s title has the power to condense everything except diamonds into a kind of super-dense dust. The solvent is accidentally spilled and, as it dissolves everything in its path, it bores a cylindrical shaft into the center of the planet. As part of a recovery effort, a makeshift platform is constructed that descends into the shaft in free fall, automatically deploying an electric motor and wheels as it approaches zero gravity, then using rocket engines to enable it to ascend again to the Earth’s surface. The author Rosa describes this fantasy journey in great detail: the supposed structure of the Earth is illustrated, and the shaft is kept in a vacuum to protect against the lethal several thousand kilometers of atmosphere that it would otherwise be exposed to. The ducks must wear space suits and go without food for several days, and they are not entirely certain that the super-dense heat shield will hold. The author maintains continuity with Carl Barks, explaining that the earthquakes in the story are created by spherical Fermies and Terries.

          In Tales to Astonish #2 (1959) “I Fell to the Center of the Earth”, an archaeologist named Dr. Burke who is on an expedition to Asia travels to the center of the Earth (and also, as he later finds out, backwards in time)–and encounters neanderthals and dinosaurs.

         In the Doctor Who episode, “The Runaway Bride”, a Racnoss warship is found at the center of the planet.

Picture Credit : Google

 

          The outer core begins at a depth of 2935km (1822 miles) below the Earth’s surface. It is a further 3432km (2134 miles) to the very centre of the Earth.

          Earth’s core is the very hot, very dense center of our planet. The ball-shaped core lies beneath the cool, brittle crust and the mostly-solid mantle. The core is found about 2,900 kilometers (1,802 miles) below Earth’s surface, and has a radius of about 3,485 kilometers (2,165 miles).

          Planet Earth is older than the core. When Earth was formed about 4.5 billion years ago, it was a uniform ball of hot rock. Radioactive decay and leftover heat from planetary formation (the collision, accretion, and compression of space rocks) caused the ball to get even hotter. Eventually, after about 500 million years, our young planet’s temperature heated to the melting point of iron—about 1,538° Celsius (2,800° Fahrenheit). This pivotal moment in Earth’s history is called the iron catastrophe.

          The iron catastrophe allowed greater, more rapid movement of Earth’s molten, rocky material. Relatively buoyant material, such as silicates, water, and even air, stayed close to the planet’s exterior. These materials became the early mantle and crust. Droplets of iron, nickel, and other heavy metals gravitated to the center of Earth, becoming the early core. This important process is called planetary differentiation.

          Earth’s core is the furnace of the geothermal gradient. The geothermal gradient measures the increase of heat and pressure in Earth’s interior. The geothermal gradient is about 25° Celsius per kilometer of depth (1° Fahrenheit per 70 feet). The primary contributors to heat in the core are the decay of radioactive elements, leftover heat from planetary formation, and heat released as the liquid outer core solidifies near its boundary with the inner core. 

          Unlike the mineral-rich crust and mantle, the core is made almost entirely of metal—specifically, iron and nickel. The shorthand used for the core’s iron-nickel alloys is simply the elements’ chemical symbols.

          Elements that dissolve in iron, called siderophiles, are also found in the core. Because these elements are found much more rarely on Earth’s crust, many siderophiles are classified as “precious metals.” Siderophile elements include gold, platinum, and cobalt. 

          Another key element in Earth’s core is sulfur—in fact 90% of the sulfur on Earth is found in the core. The confirmed discovery of such vast amounts of sulfur helped explain a geologic mystery: If the core was primarily, why wasn’t it heavier? Geoscientists speculated that lighter elements such as oxygen or silicon might have been present. The abundance of sulfur, another relatively light element, explained the conundrum.

Picture Credit : Google

          The crust is the hard, outer layer of the Earth that forms the land and the ocean floor. The continental crust (the lane masses) is the oldest and thickest part and made up mostly of silica and aluminium. The oceanic crust, made up mostly of silica and magnesium, is around 200 million years old.

          Early on in Earth’s history, minerals began to form. Lighter minerals floated up toward the surface and formed a thin crust of rock around the outside of the planet (which we now live on top of). If Earth was the size of a plum, the rocky crust would be a bit like the thin purple skin. If we want to see below the surface, we can drill down into the crust for thousands of meters.

          The crust is mostly made of minerals such as quartz, feldspar and mica. These are the shiny crystals in granite rocks, which you can see in the southwest of Kenya. Over long periods of time these minerals break down into small pieces and are carried around by winds, currents and waves to form soft sediments like sand. Look out for sediments when you are by a river, a lake or a beach.

          The crust is made up of huge blocks of rock that move around the Earth’s surface very slowly – as slowly as your fingernails grow. The movement of these plates over millions of years causes continents to split apart and smash together. Right now, East Africa is splitting into two pieces along the Great Rift Valley and one day in the distant future, the rift may be flooded by the sea.

          In between the core and the crust is a hot, squishy body of rock called the mantle. The mantle is mostly made of a mineral called olivine, which is a beautiful shade of green. The hot mantle has currents that flow like treacle. These slow currents push the plates of rock around at the surface.

Picture Credit : Google