EARTH AND ITS INTERIOR

OVERVIEWI. INTRODUCTIONII. CHRONOLOGYIII. COMPOSITION & STRUCTUREIV. SURFACEV. TECTONIC PLATESVI. HYDROSPHERE & ATMOSPHEREVII. WEATHER & CLIMATEVIII. MAGNETIC FIELDIX. ROTATION & ORBITX. BIOSPHEREXI. INTERNAL STRUCTUREXII. FUTURE

I. INTRODUCTION

The name "Earth" was derived from the Anglo-Saxon word erda, which means ground or soil. It became eorthe in Old English, then erthe in Middle English.

The standard astronomical symbol of the Earth consists of a cross circumscribed by a circle. Earth is the third planet from the Sun, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density. It is also referred to as the World, Blue Planet, and Terra.

Earth’s astronomical symbol

II. CHRONOLOGY

• 4.54 billion years ago, the earth was formed.• Within 10-20 million years, the assembly of the earth was completed.• The moon soon formed afterwards as a result of a mars sized

object impacting the earth.• In hundreds of millions of years, the surface continually reshaped as continents formed and broke up.• 780 million years ago (Ma), super continents Rodinia broke

apart.• The continents later combined to form Pannotia about 600-540

Ma. Then finally Pangea which broke apart 180 Ma.

Rodinia

Pannotia

The Super Continents

III. COMPOSITION & STRUCTURE

Earth is a terrestrial planet, the largest of the four terrestrial planets in terms of size, mass, density, surface, gravity, magnetic field, and rotation.

• Shape:-Oblate spheroid with a bulge around the equator.

• Composition:-Mass is approximately 5.98x1024 kg.

-composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%); with the remaining 1.2% consisting of trace amounts of other elements.

•Heat:-80% of total heat comes from radioactive decay and 20% from planetary accretion.

-Total heat loss is about 4.2x1013 watts.

Earth compared to other terrestrial planets

A terrestrial planet, telluric planet, rocky planet or inner planet is a planet that is primarily composed of silicate rocks. Within the solar system, the terrestrial planets are the closest planets to the Sun. The terms are derived from Latin words for Earth (Terra and Tellus), and an alternative definition would be that these are planets which are, in some notable fashion, "Earth-like".Terrestrial planets are substantially different from gas giants, which might not have solid surfaces and are composed mostly of some combination of hydrogen, helium, and water existing in various physical states.

Isotope Heat release [W/kg

isotope]

Half-life [years]

Mean mantle concentration [kg isotope/kg

mantle]

Heat release [W/kg

mantle]

238U 9.46 × 10-5 4.47 × 109 30.8 × 10-9 2.91 × 10-12

235U 5.69 × 10-4 7.04 × 108 0.22 × 10-9 1.25 × 10-13

232Th 2.64 × 10-5 1.40 × 1010 124 × 10-9 3.27 × 10-12

40K 2.92 × 10-5 1.25 × 109 36.9 × 10-9 1.08 × 10-12

Present day heat-producing isotopes

IV. SURFACE

• 70.8% is water and 29.2% is composed of land masses.

• Pedosphere – outermost layer comprised of soil. Exists at the interface of lithosphere, atmosphere, hydrosphere, and biosphere.

Land Use: Percentage:

Arable land: 13.13%

Permanent crops: 4.71%

Permanent pastures: 26%

Forests and woodland:

32%

Urban areas: 1.5%

Other: 30%

Land Usage by Humans:

V. TECTONIC PLATES

3 Types of Plate Boundaries:

• Convergent Boundaries

• Divergent Boundaries

• Transform Boundaries

• Plates ride on top of the asthenosphere, the solid but less-viscous part of the upper mantle that can flow and move along with the plates, and their motion is strongly coupled with patterns convection inside the Earth's mantle.

• As the tectonic plates migrate across the planet, the ocean floor is subducted under the leading edges of the plates at convergent boundaries. At the same time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges.

•The combination of the tectonic processes recycles oceanic crust back into the mantle.

Tectonic Plates

Plate tectonics (from the Greek τέκτων; tektōn, meaning "builder" or "mason") describes the large scale motions of Earth's lithosphere. The theory encompasses the older concepts of continental drift, developed during the first decades of the 20th century by Alfred Wegerner, and seafloor spreading, understood during the 1960s.

The oceanic and continental crust

VI. HYDROSPHERE & ATMOSPHERE

• Hydrosphere

- consists chiefly of oceans.

- deepest underwater location is Challenger Deep of the Mariana Trench in the Pacific with a depth of –10, 911.4 m.

- mass of oceans is approximately 1.35x1018 metric tons and volume is 1.386x1019 km3.

- 97.5% of the water is saline and 2.25% is freshwater – 68.7% in the form of ice.

• Atmosphere

- atmospheric pressure on the surface is 101.32 kPa with a height of 8.5 km.

- It is 78% nitrogen and 21% oxygen, with trace amounts of water vapor, carbon dioxide and other gaseous molecules.

- important part is the ozone layer.

- atmosphere leaks steadily into space due to thermal energy.

Earth’s atmosphere layers

Exosphere From 500–1,000 km (310–620 mi; 1,600,000–3,300,000 ft) up to 10,000 km (6,200 mi; 33,000,000 ft), contain free-moving particles that may migrate into and out of the magnetosphere or the solar wind.

Exobase Also known as the 'critical level', it is the lower boundary of the exosphere.

Ionosphere The part of the atmosphere that is ionized by solar radiation stretches from 50 to 1,000 km (31 to 620 mi; 160,000 to 3,300,000 ft) and typically overlaps both the exosphere and the thermosphere. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere. Because of its charged particles, it has practical importance because it influences radio propagation on the Earth. It is responsible for auroras.

Thermopause The boundary above the thermosphere, it varies in height from 500–1,000 km (310–620 mi; 1,600,000–3,300,000 ft).

Thermosphere From 80–85 km (50–53 mi; 260,000–280,000 ft) to over 640 km (400 mi; 2,100,000 ft), temperature increasing with height. The temperature of this layer can rise to 1,500 °C (2,730 °F). The International Space Station orbits in this layer, between 320 and 380 km (200 and 240 mi).

Mesopause The temperature minimum at the boundary between the thermosphere and the mesosphere. It is the coldest place on Earth, with a temperature of −100 °C (−148.0 °F; 173.1 K).

Mesosphere From the Greek word "μέσος" meaning middle. The mesosphere extends from about 50 km (31 mi; 160,000 ft) to the range of 80–85 km (50–53 mi; 260,000–280,000 ft). Temperature decreases with height, reaching −100 °C (−148.0 °F; 173.1 K) in the upper mesosphere. This is also where most meteors burn up when entering the atmosphere.

Stratopause The boundary between the mesosphere and the stratosphere, typically 50 to 55 km (31 to 34 mi; 160,000 to 180,000 ft). The pressure here is 1/1000th sea level.

Stratosphere From the Latin word "stratus" meaning spreading out. The stratosphere extends from the troposphere's 7–17 km (4.3–11 mi; 23,000–56,000 ft) range to about 51 km (32 mi; 170,000 ft). Temperature increases with height. The stratosphere contains the ozone layer, the part of the Earth's atmosphere which contains relatively high concentrations of ozone. "Relatively high" means a few parts per million—much higher than the concentrations in the lower atmosphere but still small compared to the main components of the atmosphere. It is mainly located in the lower portion of the stratosphere from approximately 15–35 km (9.3–22 mi; 49,000–110,000 ft) above Earth's surface, though the thickness varies seasonally and geographically.

Ozone Layer Though part of the Stratosphere, the ozone layer is considered as a layer of the Earth's atmosphere in itself because its physical and chemical composition is far different from the Stratosphere. Ozone (O3) in the Earth's stratosphere is created by ultraviolet light striking oxygen molecules containing two oxygen atoms (O2), splitting them into individual oxygen atoms (atomic oxygen); the atomic oxygen then combines with unbroken O2 to create O3. O3 is unstable (although, in the stratosphere, long-lived) and when ultraviolet light hits ozone it splits into a molecule of O2 and an atom of atomic oxygen, a continuing process called the ozone-oxygen cycle. This occurs in the ozone layer, the region from about 10 to 50 km (33,000 to 160,000 ft) above Earth's surface. About 90% of the ozone in our atmosphere is contained in the stratosphere. Ozone concentrations are greatest between about 20 and 40 km (66,000 and 130,000 ft), where they range from about 2 to 8 parts per million.

Tropopause The boundary between the stratosphere and troposphere.

Troposphere From the Greek word "τρέπω" meaning to turn or change. The troposphere is the lowest layer of the atmosphere; it begins at the surface and extends to between 7 km (23,000 ft) at the poles and 17 km (56,000 ft) at the equator, with some variation due to weather factors. The troposphere has a great deal of vertical mixing because of solar heating at the area. This heating makes air masses less dense so they rise. When an air mass rises, the pressure upon it decreases so it expands, doing work against the opposing pressure of the surrounding air. The troposphere contains roughly 80% of the total mass of the atmosphere. Fifty percent of the total mass of the atmosphere is located in the lower 5.6 km (18,000 ft) of the troposphere.

VII. WEATHER & CLIMATE

• The sun heats the troposphere & the surface causing air expansion.

• Ocean currents are important factors in determining climate.

• Water cycle is a vital mechanism for supporting life on land.

• The Earth can be sub-divided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the tropical (or equatorial), subtropical, temperate and polar climates.

• Climate can also be classified based on the temperature and precipitation, with the climate regions characterized by fairly uniform air masses.

Map of Ocean Currents

An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon the water, such as the Earth's rotation, wind, temperature, salinity differences and tides caused by the gravitational pull of the Moon and the Sun. Depth contours, shoreline configurations and interaction with other currents influence a current's direction and strength.

Earth’s climate zones

VIII. MAGNETIC FIELD

• Magnetic field is shaped roughly as a magnetic dipole.

• Field is generated within the molten outer core region where heat creates convection motions.

• Convection movements are chaotic and periodically change alignment resulting in field reversals.

• Field forms the magnetosphere which deflects particles in the solar wind.

• Collision between magnetic field and the solar wind forms the Van Allen radiation belts.

• Aurora is formed after plasma enters the earth’s atmosphere at magnetic poles.

Field Reversal

Earth’s Magnetosphere blocking the solar wind

The magnetosphere shields the surface of the Earth from the charged particles of the solar wind and is generated by electric currents located in many different parts of the Earth. It is compressed on the day (Sun) side due to the force of the arriving particles, and extended on the night side. (Image not to scale.)

Van Allen Radiation Belts

Aurora

Auroras, sometimes called the northern and southern (polar) lights or auroras are natural light displays in the sky, usually observed at night, particularly in the polar regions. They typically occur in the ionosphere.

IX. ROTATION AND ORBIT• Rotation

- earth’s rotation period relative to the sun (solar day) is 86,400 seconds of mean solar time.

- rotation relative to fixed stars (stellar day) is 86,14.098903691 seconds of mean solar time.

- rotation relative to moving mean vernal equinox (sidereal day) is 86,164.09053083288 seconds of mean solar time.

• Orbit

- earth orbits the sun at an average distance of 150 million km every 365.256 mean solar days. Orbital speed averages 30 km/s.

- moon revolves around earth every 27.32 days relative to background stars.

- earth’s axis is tilted some 23.5 degrees from the perpendicular to the earth-sun plane.

- earth-moon plane is tilted about 5 degrees against earth-sun plane.

Earth’s Rotation

Earth’s axial tilt and obliquity

X. BIOSPHERE

The planet's life forms are sometimes said to form a "biosphere". This biosphere is generally believed to have begun evolving about 3.5 billion years ago. Earth is the only place in the universe where life is known to exist. Some scientists believe that Earth-like biospheres might be rare.

The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth. From the broadest biophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, hydrosphere, and atmosphere.

XI. INTERNAL STRUCTURE

• Structure

- mechanically divided into lithosphere, asthenosphere, mesosphere, outer core, and the inner core.

- chemically divided into the crust, upper mantle, lower mantle, outer core, and the inner core.

• Core

- average density of earth is 5,515 kg/m3.

- divided into a solid inner core, radius of 1220 km, and liquid outer core, radius of 3,400 km.

- temperature in the inner core is around 7000 degrees Celsius and around 4000-6000 degrees Celsius in the outer core.

- believed to largely be composed of iron (80%), along with nickel and one or more lighter elements.

- the liquid outer core is believed to be composed of iron mixed with nickel and traces of lighter elements.

• Mantle

- extends to a depth of 2,890 km.

- pressure at the bottom is about 140 Gpa and temperature is around 870 degrees Celsius.

- composed of silicate rock rich in iron and magnesium.

- high temperature within the mantle causes silicate material to be sufficiently ductile.

- viscosity ranges between 1021 and 1024 Pa-s depending on depth.

• Crust

- the outermost layer, ranging from 5-70 km in depth.

- thin parts are the oceanic crust composed of dense iron magnesium silicate rocks, and underlie the ocean basins.

- thicker crust is continental crust , less dense and composed of sodium potassium aluminum silicate rocks.

- most of rocks making the earth’s crust formed less than 100 Ma.

- oldest known mineral grains are 4.4 billion years old.

Earth’s Interior Cut-out

Internal structure of the earth

XII. FUTURE

• Future of earth is closely tied to the sun. Luminosity of the sun will grow by 10% over the next Gyr and by 40% over the next 3.5 Gyr.

• Rise in radiation reaching earth may result in loss of oceans.

• Increasing surface temperature will accelerate CO2 cycle making it lethal in 900 million years.

• Animal life will become extinct within several million more years.

• Mean global temperature will reach 70 degrees C after another billion years and all surface water will disappear.

• Sun will become a red giant in about 5 Gyr. Earth may escape envelopment by the sun or it may cause the earth’s orbit to decay and enter the sun’s atmosphere eventually leading to earth’s destruction.

Life Cycle of the Sun

The Sun is about halfway through its main-sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. Each second, more than 4 million tons of matter are converted into energy within the Sun's core, producing neutrinos and solar radiation; at this rate, the Sun will have so far converted around 100 Earth-masses of matter into energy. The Sun will spend a total of approximately 10 billion years as a main sequence star.

The Sun does not have enough mass to explode as a supernova. Instead, in about 5 billion years, it will enter a red giant phase, its outer layers expanding as the hydrogen fuel in the core is consumed and the core contracts and heats up. Helium fusion will begin when the core temperature reaches around 100 million Kelvin and will produce carbon, entering the asymptotic giant branch phase.

The sun as a Red Giant

A red giant is a luminous giant star of low or intermediate mass (roughly 0.5–10 solar masses) that is in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower.

The solar system’s clockwork motion is by no means guaranteed, for new computer simulations suggests a slight chance that a disruption of planetary orbits could lead to a collision of Earth with Mercury, Mars or Venus in future.

END