My Science School

As Earth spins, different parts of its surface turn towards the Sun at different times - the Sun is always rising in one place and setting in another. So, the time of day varies around the world. When it’s dawn where you live, it’s sunset on the other side of the world. To make it easier to set clocks, the world is split into 24 time zones, one for each hour of the day. As you go east around the world, you put clocks forward by one hour for each zone - until you reach an imaginary line called the International Date Line. If you go further on across the Date Line, you carry on adding hours, but put the calendar back by a day.

A time zone is a region on Earth that uses a uniform time. They are often based on the boundaries of countries or lines of longitude. Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory located in Greenwich, London, considered to be located at a longitude of zero degrees. Although GMT and Coordinated Universal Time (UTC) essentially reflect the same time, GMT is a time zone, while UTC is a time standard that is used as a basis for civil time and time zones worldwide. Although GMT used to be a time standard, it is now mainly used as the time zone for certain countries in Africa and Western Europe. UTC, which is based on highly precise atomic clocks and the Earth's rotation, is the new standard of today.

UTC is not dependent on daylight saving time (DST), though some countries switch between time zones during their DST period, such as the United Kingdom using British Summer Time in the summer months.

Most time zones that are on land are offset from UTC. UTC breaks time into days, hours, minutes, and seconds, where days are usually defined in terms of the Gregorian calendar. Generally, time zones are defined as + or - an integer number of hours in relation to UTC; for example, UTC-05:00, UTC+08:00, and so on. UTC offset can range from UTC-12:00 to UTC+14:00. Most commonly, UTC is offset by an hour, but in some cases, the offset can be a half-hour or quarter-hour, such as in the case of UTC+06:30 and UTC+12:45

Credit: calculator.net

Picture credit: Google

Earth's Crust

The crust is what we live on and is by far the thinnest of the layers of earth. The thickness varies depending on where you are on earth, with oceanic crust being 5-10 km and continental mountain ranges being up to 30-45 km thick. Thin oceanic crust is denser than the thicker continental crust and therefore 'floats' lower in the mantle as compared to continental crust. You will find some of the thinnest oceanic crust along mid ocean ridges where new crust is actively being formed. In comparison, when two continents collide as in the case of the India Plate and Eurasia Plate, you get some of the thickest sections of crust as it is crumpled together.

The temperatures within Earth's crust will vary from air temperatures at the surface to approximately 870 degrees Celsius in deeper sections. At this temperature, you begin to melt rock and form the below-lying mantle. Geologists subdivide Earth's crust into different plates that move about in relation to one another.

Given that Earth's surface is mostly constant in area, you cannot make crust without destroying a comparable amount of crust. With convection of the underlying mantle, we see insertion of mantle magma along mid ocean ridges, constantly forming new oceanic crust. However, to make room for this, oceanic crust must subduct (sink below) continental crust.  Geologists have studied extensively the history of this plate movement, but we are sorely lacking in determining why and how these plates move the way they do.

Earth's crust "floats" on top of the soft plastic-like mantle below. In some instances mantle clearly drives changes in the crust, as in the Hawaiian Islands. However, there is ongoing debate whether oceanic crust subduction and mid ocean ridge spreading is driven by a push or pull mechanism.

In very broad terms, oceanic crust is made up of basalt and continental crust is made up of rocks similar to granite. Below the crust is a solid relatively cooler portion of the upper mantle that is combined with the crust to make the  lithosphere layer. The lithosphere is physically distinct from the below-lying layers due to its cool temperatures and typically extends 70-100 km in depth.

Below the lithosphere is the asthenosphere layer, a much hotter and malleable portion of the upper mantle. The asthenosphere begins at the bottom of the lithosphere and extends approximately 700 km into the Earth. The asthenosphere acts as the lubricating layer below the lithosphere that allows the lithosphere to move over the Earth's surface.

Credit: Forbes

Picture credit: Google

The Earth's outer core is in a state of turbulent convection as the result of radioactive heating and chemical differentiation. This sets up a process that is a bit like a naturally occurring electrical generator, where the convective kinetic energy is converted to electrical and magnetic energy. Basically, the motion of the electrically conducting iron in the presence of the Earth's magnetic field induces electric currents. Those electric currents generate their own magnetic field, and as the result of this internal feedback, the process is self-sustaining so long as there is an energy source sufficient to maintain convection.

Unlike Mercury, Venus, and Mars, Earth is surrounded by an immense magnetic field called the magnetosphere. Generated by powerful, dynamic forces at the center of our world, our magnetosphere shields us from erosion of our atmosphere by the solar wind (charged particles our Sun continually spews at us), erosion and particle radiation from coronal mass ejections (massive clouds of energetic and magnetized solar plasma and radiation), and cosmic rays from deep space. Our magnetosphere plays the role of gatekeeper, repelling this unwanted energy that’s harmful to life on Earth, trapping most of it a safe distance from Earth’s surface in twin doughnut-shaped zones called the Van Allen Belts.

But Earth’s magnetosphere isn’t a perfect defense. Solar wind variations can disturb it, leading to “space weather” -- geomagnetic storms that can penetrate our atmosphere, threatening spacecraft and astronauts, disrupting navigation systems and wreaking havoc on power grids. On the positive side, these storms also produce Earth’s spectacular aurora. The solar wind creates temporary cracks in the shield, allowing some energy to penetrate down to Earth’s surface daily. Since these intrusions are brief, however, they don’t cause significant issues.

Credit: NASA

Picture credit: Google

Because as Earth cooled, dense metal like iron sank to the centre, while lighter rock-forming materials floated to the top.

At the center of Earth is a solid iron inner core. The hot dense core has a radius of about 759 miles (1,221 kilometers) and a pressure of about 3.6 million atmospheres (atm). 

Temperatures in the inner core are about as hot as the surface of the sun (about 9,392 degrees F or 5,200 degrees C) — more than hot enough to melt iron — but the immense pressure from the rest of the planet keeps the inner core solid, according to National Geographic.

The primary contributors to the inner core's heat are the decay of radioactive elements such as uranium, thorium and potassium in Earth's crust and mantle, residual heat from planetary formation, and heat emitted by the solidification of the outer core.

Earth's inner core rotates in the same direction as the surface of the planet but rotates ever so slightly faster, completing one extra rotation every 1,000 years or so.

Credit: space.com

Picture credit: Google

Plates move at an average of between four and seven centimetres in a year. If plates collide along a deep trench beneath an ocean, one plate is pulled beneath another and melts and is recycled. On land, when continents collide, their edges are pushed up into new mountain ranges.

When two tectonic plates collide, they form a convergent plate boundary. 

• A convergent plate boundary such as the one between the Indian Plate and the Eurasian Plate forms towering mountain ranges, like the Himalayas, as Earth’s crust is crumpled and pushed upward. 
• In some cases, however, a convergent plate boundary can result in one tectonic plate diving underneath another. This process is called subduction. It involves an older, denser tectonic plate being forced deep into the planet underneath a younger, less-dense tectonic plate. When this process occurs in the ocean, a trench can be formed.
• When subduction occurs, a chain of volcanoes often develops near the convergent plate boundary.

Credit: Byju’s

Picture credit: Google

The structure of Earth can be divided into three parts: the crust, the mantle and the core. Made up from mainly oxygen and silicon, the crust is the outermost layer. It is the familiar landscape on which we live: rocks, soil and seabed. Beneath the crust is the mantle, a layer almost 3000 km deep. It is made of metal silicates, sulphides and oxides. This layer is so hot that the rock often flows like sticky road tar - only very, very slowly. Below the mantle is a core of metal, mostly iron, sulphur and nickel. The outer portion of the core is so very hot that the metal is always molten. The Earth’s magnetic field is created here. Earth’s inner core is even hotter - estimated to be around 6000 °C - but the metal is solid because pressure within the inner core is extreme, so the metal cannot melt.

1: The Core

The composition of the Earth begins with the inner parts of the planet. The Earth’s core is the densest part of the planet. It is made up of iron and nickel, and the core is so hot that is heats the rest of the planet around it. The core has chosen how the planet will be heated, and the core of the planet determines the equilibrium of the planet itself.

2: The Magma

The magma underneath the Earth’s surface spins around the world as it keeps the crust warm. The warmth of the magma can be felt in certain parts of the world where the ground is very close to the magma. The magma can be found rising out of the surface of the Earth at volcanoes and underwater cracks in the crust. The magma is the lifeblood of the Earth even though it is quite a scary thing to encounter today.

3: The Crust

The crust of the Earth is the ground that everyone walks on today. The crust is much thinner than the other components of the Earth, but it manages to support all the life on the planet. The Earth’s surface is covered with the crust completely, but much of the Earth’s surface is covered in water. Citizens of the Earth may never explore the floor of the sea, but that area is still a part of the Earth’s crust.

4: Magnetism

The magnetism of the Earth that helps it stay attached to the sun in orbit comes directly from the core. The core’s construction keeps the magnetism of the Earth going in ways that scientists do not understand completely. The magnetism created by the core also helps the Earth create a gravitational field that keeps everyone on the planet.

Credit: AES 

Picture credit: Google

Scientists have worked this out from the vibrations from earthquakes and underground explosions. This data is pictured with lines on 3D maps to help scientists understand the structure of Earth’s core.

Core, mantle, and crust are divisions based on composition. The crust makes up less than 1 percent of Earth by mass, consisting of oceanic crust and continental crust is often more felsic rock. The mantle is hot and represents about 68 percent of Earth’s mass. Finally, the core is mostly iron metal. The core makes up about 31% of the Earth.

CRUST AND LITHOSPHERE

Earth’s outer surface is its crust; a cold, thin, brittle outer shell made of rock. The crust is very thin, relative to the radius of the planet. There are two very different types of crust, each with its own distinctive physical and chemical properties.Oceanic crust is composed of magma that erupts on the seafloor to create basalt lava flows or cools deeper down to create the intrusive igneous rock gabbro. Sediments, primarily muds and the shells of tiny sea creatures, coat the seafloor. Sediment is thickest near the shore where it comes off the continents in rivers and on wind currents.

MANTLE
The two most important things about the mantle are: (1) it is made of solid rock, and (2) it is hot. Scientists know that the mantle is made of rock based on evidence from seismic waves, heat flow, and meteorites. The properties fit the ultramafic rock peridotite, which is made of the iron- and magnesium-rich silicate minerals. Peridotite is rarely found at Earth’s surface.Scientists know that the mantle is extremely hot because of the heat flowing outward from it and because of its physical properties. Heat flows in two different ways within the Earth: conduction and convection. Conduction is defined as the heat transfer that occurs through rapid collisions of atoms, which can only happen if the material is solid. Heat flows from warmer to cooler places until all are the same temperature. The mantle is hot mostly because of heat conducted from the core. Convection is the process of a material that can move and flow may develop convection currents.

CORE
At the planet’s center lies a dense metallic core. Scientists know that the core is metal for a few reasons. The density of Earth’s surface layers is much less than the overall density of the planet, as calculated from the planet’s rotation. If the surface layers are less dense than average, then the interior must be denser than average. Calculations indicate that the core is about 85 percent iron metal with nickel metal making up much of the remaining 15 percent. Also, metallic meteorites are thought to be representative of the core.If Earth’s core were not metal, the planet would not have a magnetic field. Metals such as iron are magnetic, but rock, which makes up the mantle and crust, is not. Scientists know that the outer core is liquid and the inner core is solid because S-waves stop at the inner core. The strong magnetic field is caused by convection in the liquid outer core. Convection currents in the outer core are due to heat from the even hotter inner core. The heat that keeps the outer core from solidifying is produced by the breakdown of radioactive elements in the inner core.

Credit: Lumen Learning

Picture credit: Google

Earth is the third planet from the Sun in our Solar System. From a distance, it looks like a great, round, blue jewel hanging in the darkness of space. It is blue because three-quarters of its rocky surface is submerged under blue, ocean waters, which shimmer in the light of the Sun.

The way light reflects off air molecules has an effect on the way people see the sky as well as the ocean. When orbiting the Earth, satellites and astronauts see a blue globe due to some of these same properties. The sheer amount of water on Earth makes it appear blue in these instances, but there are other factors as well.

Scattering in the Atmosphere

The atmosphere is predominantly made of two gases, nitrogen and oxygen. These molecules absorb and scatter, or radiate, different kinds of light. Red, yellow and orange light have longer wavelengths that are not affected by as much by atmospheric gases, so they are not absorbed, but blue light is scattered and radiated, creating the blue sky you see every day. That blue light is not as visible from space, but plays a role in the blue color of the Earth. At night, the sunlight no longer is around to interact with the gases, so the sky become black.

Water Coverage

The Earth has many oceans and seas, from the Arctic Ocean to the Southern Ocean. Although there is red-hot heat below the surface of the Earth, the top layer is dominated by water. The oceans cover about 71 percent of the Earth and are blue, while land makes up the other 29 percent and varies in color, from green to tan to white. This gives the Earth the appearance of a blue marble. If the planet consisted mainly of land masses, it would be appear to be a different color completely.

Water Color

Although water covers a large percentage of the Earth, it is important to understand why the water is blue as well. As with the Earth's atmosphere, most of the colors of the light spectrum are absorbed by the water. The water radiates the blue in the spectrum, giving it its blue color. If another color were radiated, say red for instance, the Earth would look red from outer space, like Mars. The land masses of the Earth do not look blue due to this same principle.

Some Contradictions

The Earth only appears blue if you are looking at it from outer space on the side that is being lit by the sun. When you are orbiting the Earth, it will appear black when you orbit around a part of the Earth that is experiencing night. Because there is no sun to create the light, all of the Earth will appear somewhat dark. The stars will be more visible as well during this period. Land masses will appear somewhat dark blue, as there are artificial light sources that illuminate the sky on land.

Credit: Sciencing

Picture credit: Google

Earth's average orbital speed is about 30 kilometers per second. In other units, that's about 19 miles per second, or 67,000 miles per hour, or 110,000 kilometers per hour (110 million meters per hour).

Let's calculate that. First of all we know that in general, the distance you travel equals the speed at which you travel multiplied by the time (duration) of travel. If we reverse that, we get that the average speed is equal to the distance traveled over the time taken.

We also know that the time it takes for the Earth to go once around the Sun is one year. So, in order to know the speed, we just have to figure out the distance traveled by the Earth when it goes once around the Sun. To do that we will assume that the orbit of the Earth is circular (which is not exactly right, it is more like an ellipse, but for our purpose a circle is close enough). So the distance traveled in one year is just the circumference of the circle. (Remember, the circumference of a circle is equal to 2×?×radius.)

The average distance from the Earth to the Sun is about 149,600,000 km. (Astronomers call this an astronomical unit, or AU for short.) Therefore, in one year, the Earth travels a distance of 2×?×(149,600,000 km). This means that the speed is about:

speed = 2×?×(149,600,000 km)/(1 year)

and if we convert that to more meaningful units (knowing that there are, on average, about 365.25 days in a year, and 24 hours per day) we get:

speed = 107,000 km/h (or, if you prefer, 67,000 miles per hour)

So the Earth moves at about 110,000 km/h around the Sun (which is about one thousand times faster than the typical speed of a car on a highway!)

Credit: Ask an Astronomer

Picture credit: Google

You need to know two things: how long it takes to make a full rotation, and Earth’s circumference. The time it takes Earth to rotate so the sun appears in the same position in the sky, known as a solar day, is 24 hours. However, the time it takes Earth to complete one full rotation on its axis with respect to distant stars is actually 23 hours 56 minutes 4.091 seconds, known as a sidereal day.

With this information, to work out how fast Earth is spinning we need only our planet’s circumference. At the equator, its circumference is roughly 40,075 kilometres, so dividing this by the length of day means that, at the equator, Earth spins at about 1670 kilometres per hour.

However, this speed of rotation isn’t consistent across the planet. As you move north or south, the circumference of Earth gets smaller, so the speed of spin reduces until it reaches its slowest at both poles. And all of this is nothing compared with the 107,000 kilometres per hour at which Earth orbits the sun.

Credit: newscientist

Picture credit: Google

The Polish astronomer, Nicolaus Copernicus revolutionised astronomy with his discovery that the earth moved around the sun. The revelation completely changed our understanding of our place in the universe, and consequently helped herald in the age Enlightenment.

When Copernicus published his treatise ‘On the Revolutions of Heavenly Spheres’ the world was, in many ways, already waiting for a game-changer in astronomical theory. As Dr Micha? Bejger from the Polish Academy of Sciences explains: “There were enough detailed observations and frustration around trying to fix old theories, along with the advancement in mathematics, that meant Copernicus was better able to demonstrate the details of the model, and ‘get through to people’”.

The crucial elements to the theory that the earth revolved around the sun, and not the other way around, had been around for thousands of years, but it was Copernicus’ superior education in Islamic and European astronomy, coupled with the advancement in mathematics, that ultimately led to the ground-breaking discovery. “It was a classic example of an academic revolution,” says Bejger.

Credit: The first news

Picture credit: Google

Wrapped around Earth is a thin blanket of gases, including nitrogen, oxygen, argon and carbon dioxide. This blanket is called the atmosphere; its thickness is about 96.56 km. Yet without it, Earth would be as lifeless as the Moon. The atmosphere gives us air to breathe and clean water to drink, as well as protecting us from the Sun’s harmful rays, all while keeping us warm with trapped heat.

Without the protective layer of gases that make up Earth's atmosphere, the harsh conditions of the solar system would render the planet a barren, lifeless husk like the moon. The Earth's atmosphere protects and sustains the planet's inhabitants by providing warmth and absorbing harmful solar rays. In addition to containing the oxygen and carbon dioxide, which living things need to survive, the atmosphere traps the sun's energy and wards off many of the dangers of space.

Temperature

One of the most important benefits the atmosphere provides is maintaining the Earth’s temperature. On the moon, which has no protective atmosphere, temperatures can range from 121 degrees Celsius in the sun (250 degrees Fahrenheit) to negative 157 degrees Celsius in the shade (negative 250 degrees Fahrenheit). On Earth, however, molecules in the atmosphere absorb the sun’s energy as it arrives, spreading that warmth across the planet. The molecules also trap reflected energy from the surface, preventing the night side of the planet from becoming too cold.

Radiation

The atmosphere serves as a protective shield against radiation and cosmic rays. The sun bombards the solar system with ultraviolet radiation, and without protection, that radiation can cause severe damage to skin and eyes. The ozone layer high in the Earth’s atmosphere blocks much of this radiation from reaching the surface. Dense layers of molecular gases also absorb cosmic rays, gamma rays and x-rays, preventing these energetic particles from striking living things and causing mutations and other genetic damage. Even during a solar flare, which can greatly increase the damaging output of the sun, the atmosphere is able to block most of the harmful effects.

Physical Protection

The solar system may seem like a vast and empty place, but in reality it is full of debris and small particles leftover from planetary creation or collisions in the asteroid belt. According to NASA, more than 100 tons of space debris strikes Earth every single day, mostly in the form of dust and tiny particles. When they encounter the molecules that make up Earth’s atmosphere, however, the resulting friction destroys them long before they reach the ground. Even larger meteors can break up due to the stresses of atmospheric re-entry, making catastrophic meteor strikes an incredibly rare occurrence. Without the physical protection of the atmosphere, the surface of the Earth would resemble that of the moon, pockmarked with impact craters.

Weather and Water

The atmosphere also serves an important purpose as a medium for the movement of water. Vapor evaporates out of oceans, condenses as it cools and falls as rain, providing life-giving moisture to otherwise dry areas of the continents. According to the U.S. Geological Survey, the Earth’s atmosphere holds around 12,900 cubic kilometers (3,100 cubic miles) worth of water at any given time. Without an atmosphere, it would simply boil away into space, or remain frozen in pockets below the surface of the planet.

credit: Sciencing

Picture credit: Google

At the start, it was just a fiery ball of molten (liquid) rock. As it cooled, lumps formed on the surface of the molten rock. The surface gradually hardened into a crust. Volcanoes kept on pouring steam and gases onto the surface, which led to the atmosphere being formed. As Earth cooled further, clouds of steam became water, creating vast oceans. The crust eventually cooled to form the continents.

Three recent studies improve our understanding of environmental conditions on early Earth—important not just for reconstructing the history of our own planet, but for assessing the habitability of planetary bodies in general.

The first of these studies was led by John Tarduno from the University of Rochester and reported in Proceedings of the National Academy of Sciences. The authors present evidence of a strong magnetic field around Earth, from about 4.1 billion to 4 billion years ago. Their conclusion is based on magnetite inclusions in certain minerals (zircons), and thus appears to be very reliable. A strong magnetic field would have been critical for life to originate on Earth, because it would have protected the surface from the solar wind. Stars like our Sun are known to expel large amounts of harmful radiation when they are still young, and without a magnetic field it is doubtful life on Earth’s surface would have been able to survive the barrage.

credit: smithsonianmag

Picture credit: Google

Yes, Earth spins around a line between the poles called its axis. The axis is tilted over at 23.5° in relation to the Sun. Earth rotates once every 23 hours, 56 minutes and 4.09 seconds. The Sun thus appears to come back to the same place in the sky once every 24 hours.

Earth’s spin, tilt, and orbit affect the amount of solar energy received by any particular region of the globe, depending on latitude, time of day, and time of year. Small changes in the angle of Earth’s tilt and the shape of its orbit around the Sun cause changes in climate over a span of 10,000 to 100,000 years, and are not causing climate change today.

Daily changes in light and temperature are caused by the rotation of the Earth, and seasonal changes are caused by the tilt of the Earth. As the Earth orbits the Sun, the Earth is pulled by the gravitational forces of the Sun, Moon, and large planets in the solar system, primarily Jupiter and Saturn. Over long periods of time, the gravitational pull of other members of our solar system slowly change Earth’s spin, tilt, and orbit. Over approximately 100,000 – 400,000 years, gravitational forces slowly change Earth’s orbit between more circular and elliptical shapes. Over 19,000 – 24,000 years, the direction of Earth’s tilt shifts (spins). Additionally, how much Earth’s axis is tilted towards or away from the Sun changes through time, over approximately 41,000 year cycles. Small changes in Earth’s spin, tilt, and orbit over these long periods of time can change the amount of sunlight received (and therefore absorbed and re-radiated) by different parts of the Earth. Over 10s to 100s of thousands of years, these small changes in the position of the Earth in relationship to the Sun can change the amount of solar radiation, also known as insolation, received by different parts of the Earth. In turn, changes in insolation over these long periods of time can change regional climates and the length and intensity of the seasons. The Earth’s spin, tilt, and orbit continue to change today, but do not explain the current rapid climate change.

credit: UNDERSTANDING GLOBAL CHANGE

Picture credit: Google

Earth is not quite a perfect sphere. The spinning of the planet causes it to bulge at the equator. Scientists describe Earth’s shape as ‘geoid’, which, interestingly, means ‘Earth-shaped’.

The shape of the Earth is geoid.

Earth looks like a blue marble with white swirls and areas of brown, yellow, green and white from space.

• The blue is water, which covers about 71 per cent of Earth’s surface.
• The white swirls are clouds. The areas of brown, yellow and green are land.
• The areas of white are ice and snow.

Scientists use geodesy, which is the science of measuring Earth’s shape, gravity and rotation. Geodesy provides accurate measurements that show Earth is round. Even though our planet is a sphere, it is not a perfect sphere. Because of the force caused when Earth rotates, the North and South Poles are slightly flat.

Credit: Byjus

Picture credit: Google