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Planet Earth
Earth
Earth
Planet Earth
What do you know about Planet Earth?
What should you know about Planet Earth?
What is Earth?
What does Earth look like?
How does Earth move?
What is Earth made of?
How big is Earth?
How far is Earth from the Sun?
Why do we have day and night?
Why does Earth have seasons?
What are Earth's different parts?
What is Earth's orbit period?
What is the volume of Earth?
What is the mass of Earth?
What is Earth's density?
How is the atmosphere of the earth classified?
What is Earth Science?
What are various types of pressure?

What should you know about Planet Earth?
Atmosphere of Earth
Atmospheric pressure
Asteroids and artificial satellites
Axial tilt and seasons
Air
Biosphere
Composition and structure
Cultural and historical viewpoint
Chemical composition
Earth Science
Earth’s Components
Earth Materials
Earth’s Surface
Earth’s Layers
Earth’s Interior Layers
Earth’s Magnetic Field
Earth and the Solar System
Earth's internal heat
Habitability
Human geography
Hydrosphere
Life
Magnetic field
Moon
Natural and environmental hazards
Natural resources and land use
Oceans
Orbit and rotation
Orbital characteristics
Physical characteristics
Shape
Seasons
Soil
Soil Size Classification
Tectonic plates
Upper atmosphere
Water
Weather and climate


Atmosphere of Earth

How is the atmosphere of the earth classified?
Troposphere
Stratosphere
Mesosphere
Thermosphere
Exosphere

Does the atmosphere of the Earth have an end-point boundary?
No.

How does the atmosphere of the Earth extend from its surface to outer space?
The Earth's atmosphere has no definite boundary; it slowly becomes thinner and fades into outer space. There are various objects in the solar system and universe. Up to now, 10000 km = 6213 mi 1252.9 yd above earth surface is included in the Earth’s atmosphere.

What is known about the atmosphere of Earth up to now?
Here are further guidelines.
http://www.qureshiuniversity.com/earthsatmosphere.html

10000km = 6213mi 1252.9yd
690km = 428mi 1313.2yd
85km = 52mi 1437.1yd
50km = 31mi 120.66yd
20km = 12mi 752.27yd
Km = Miles Yards


Earth Science

Atmosphere

Atmospheric chemistry
Climatology
Meteorology
Hydrometeorology
Paleoclimatology

Biosphere

Ecology
Biogeography
Paleontology
Palynology
Micropaleontology
Geomicrobiology
Geoarchaeology

Hydrosphere

Hydrology
Geohydrology
Limnology (freshwater science)
Oceanography (marine science)
Chemical oceanography
Physical oceanography
Biological oceanography (marine biology)
Geological oceanography (marine geology)
Paleoceanography

Hydrosphere

Hydrology
Geohydrology
Limnology (freshwater science)
Oceanography (marine science)
Chemical oceanography
Physical oceanography
Biological oceanography (marine biology)
Geological oceanography (marine geology)
Paleoceanography

Pedosphere

Soil science
Edaphology
Pedology

Geophysics
Geochronology
Geodynamics (see also Tectonics)
Geomagnetism
Gravimetry (also part of Geodesy)
Seismology
Glaciology
Hydrogeology
Mineralogy
Crystallography
Gemology
Petrology
Speleology
Volcanology

Systems

Environmental science
Geography
Human geography
Physical geography
Gaia hypothesis

Others

Cartography
Geoinformatics (GIS)
Geostatistics
Geodesy and Surveying

What is Earth Science?
Earth Science is the study of the Earth and its neighbors in space.

What is Earth?
Earth is our home planet. Scientists believe Earth and its moon formed around the same time as the rest of the solar system. They think that was about 4.5 billion years ago. Earth is the fifth-largest planet in the solar system. Its diameter is about 8,000 miles. And Earth is the third-closest planet to the sun. Its average distance from the sun is about 93 million miles. Only Mercury and Venus are closer.

Earth has been called the "Goldilocks planet." In the story of "Goldilocks and the Three Bears," a little girl named Goldilocks liked everything just right. Her porridge couldn't be too hot or too cold. And her bed couldn't be too hard or too soft. On Earth, everything is just right for life to exist. It's warm, but not too warm. And it has water, but not too much water.

Earth is the only planet known to have large amounts of liquid water. Liquid water is essential for life. Earth is the only planet where life is known to exist.

The Earth is divided into several layers which have distinct chemical and seismic properties (depths in km):

0- 40 Crust
40- 400 Upper mantle
400- 650 Transition region
650-2700 Lower mantle
2700-2890 D'' layer
2890-5150 Outer core
5150-6378 Inner core

Taken as a whole, the Earth's chemical composition (by mass) is:
34.6% Iron
29.5% Oxygen
15.2% Silicon
12.7% Magnesium
2.4% Nickel
1.9% Sulfur
0.05% Titanium

What does Earth look like?
From space, Earth looks like a blue marble with white swirls and areas of brown, yellow, green and white. The blue is water, which covers about 71 percent of Earth's surface. The white swirls are clouds. The areas of brown, yellow and green are land. And the areas of white are ice and snow.

The equator is an imaginary circle that divides Earth into two halves. The northern half is called the Northern Hemisphere. The southern half is called the Southern Hemisphere. The northernmost point on Earth is called the North Pole. The southernmost point on Earth is called the South Pole.

How does Earth move?
Earth orbits the sun once every 365 days, or one year. The shape of its orbit is not quite a perfect circle. It's more like an oval, which causes Earth's distance from the sun to vary during the year. Earth is nearest the sun, or at "perihelion," in January when it's about 91 million miles away. Earth is farthest from the sun, or at "aphelion," in July when it's about 95 million miles away.

What is Earth made of?
Earth is unique among the known planets: it has an abundance of water. Other worlds — including a few moons — have atmospheres, ice, and even oceans, but only Earth has the right combination to sustain life.

Earth's oceans cover about 70 percent of the planet's surface with an average depth of 2.5 miles (4 kilometers). Fresh water exists in liquid form in lakes and rivers and as water vapor in the atmosphere, which causes much of Earth's weather.

Earth has multiple layers. The ocean basins and the continents compose the crust, the outermost layer. Earth's crust is between three and 46 miles (five and 75 km) deep. The thickest parts are under the continents and the thinnest parts are under the oceans.

Crust

Earth's crust is made up of several elements: iron, 32 percent; oxygen, 30 percent; silicon, 15 percent; magnesium, 14 percent; sulfur, 3 percent; nickel, 2 percent; and trace amounts of calcium, aluminum and other elements.

The crust is divided into huge plates that float on the mantle, the next layer. The plates are constantly in motion; they move at about the same rate as fingernails grow. Earthquakes occur when these plates grind against each other. Mountains form when the plates collide and deep trenches form when one plate slides under another plate. Plate tectonics is the theory explaining the motion of these plates.

Mantle

The mantle under the crust is about 1,800 miles deep (2,890 km). It is composed mostly of silicate rocks rich in magnesium and iron. Intense heat causes the rocks to rise. They then cool and sink back down to the core. This convection — like a lava lamp — is believed to be what causes the tectonic plates to move. When the mantle pushes through the crust, volcanoes erupt.

Core

At the center of the Earth is the core, which has two parts. The solid, inner core of iron has a radius of about 760 miles (about 1,220 km). It is surrounded by a liquid, outer core composed of a nickel-iron alloy. It is about 1,355 miles (2,180 km) thick. The inner core spins at a different speed than the rest of the planet. This is thought to cause Earth's magnetic field. When charged particles from the solar wind collide with air molecules above Earth's magnetic poles, it causes the air molecules to glow, causing the auroras — the northern and southern lights.

How big is Earth?
Earth, the third planet from the sun, is the fifth largest planet in the solar system; only the gas giants Jupiter, Saturn, Uranus and Neptune are bigger. Earth is the largest of the terrestrial planets of the inner solar system, bigger than Mercury, Venus and Mars.

Radius, diameter and circumference

The mean radius of Earth is 3,959 miles (6,371 kilometers). However, Earth is not quite a sphere. The planet's rotation causes it to bulge at the equator. Earth's equatorial diameter is 7,926 miles (12,756 kilometers), but from pole to pole, the diameter is 7,900 miles (12,720 km) — a difference of only 40 miles (64 km).

The circumference of Earth at the equator is about 24,902 miles (40,075 km), but from pole-to-pole — the meridional circumference — Earth is only 24,860 miles (40,008 km) around. This shape, caused by the flattening at the poles, is called an oblate spheroid.

Density, mass and volume

Earth's density is 5.52 grams per cubic centimeter. Earth is the densest planet in the solar system because of its metallic core and rocky mantle. Jupiter, which is 318 more massive than Earth, is less dense because it is made of gases, such as hydrogen.

Earth's mass is 6.6 sextillion ton (5.9722 x 1024 kilograms). It volume is 1.08321 x 1012 km.

The total surface area of Earth is about 197 million square miles (509 million square km). About 71 percent is covered by water and 29 percent by land.

Highest and lowest points

Mount Everest is the highest place on Earth above sea level, at 29,028 feet (8,848 meters), but it is not the highest point on Earth — that is, the place most distant from the center of the Earth. That distinction belongs to Mount Chimaborazo in the Andes Mountains in Ecuador. Although Chimaborazo is about 10,000 feet shorter (relative to sea level) than Everest, this mountain is about 1.5 miles (2.4 km) farther into space because of the equatorial bulge.

The lowest point on Earth is the Mariana Trench in the western Pacific Ocean. It reaches down about 36,200 feet (11,034 meters) below sea level.

How far is Earth from the Sun?
The sun is at the heart of the solar system. All of the bodies in the solar system — planets, asteroids, comets, etc. — revolve around it. The distance from Earth to the sun is called an astronomical unit, or AU, which is used to measure distances throughout the solar system. The AU has been defined as 149,597,870,700 meters (92,955,807 miles).

Astronomers use the AU for measuring distances throughout the solar system. Jupiter, for example, is 5.2 AU from the sun. Neptune is 30.07 AU from the sun. On the outer edges of the solar system, the Oort Cloud, where comets are thought to originate, is 100,000 AU from the sun. The distance to the nearest star, Proxima Centauri, is about 250,000 AU. However, to measure longer distances, astronomers use light-years, or the distance that light travels in a single Earth year, which is equal to 63,239 AU. So Proxima Centauri is about 4.2 light-years away.

The AU is the average distance from the Earth to the sun. Earth makes a complete revolution around the sun every 365.25 days ­— one year. However, Earth's orbit is not a perfect circle; it is shaped more like an oval, or an ellipse. Over the course of a year, Earth moves sometimes closer to the sun and sometimes farther away from the sun. Earth's closest approach to the sun, called perihelion, comes in early January and is about 91 million miles (146 million km). The farthest from the sun Earth gets is called aphelion. It comes in early July and is about 94.5 million miles (152 million km).

Finding the distance

Historically, the first person to measure the distance to the sun was Aristarchus around the year 250 BC. In more recent times, astronomer Christiaan Huygens calculated the distance from Earth to the sun in 1653. He used the phases of Venus to find the angles in a Venus-Earth-Sun triangle. For example, when Venus appears half illuminated by the sun, the three bodies form a right triangle from Earth's perspective. Guessing (correctly, by chance) the size of Venus, Huygens was able to determine the distance from Venus to Earth, and knowing that distance, plus the angles made by the triangle, he was able to measure the distance to the sun. However, because Huygens' method was partly guesswork and not completely scientifically grounded, he usually doesn't get the credit.

In 1672, Giovanni Cassini used a method involving parallax, or angular difference, to find the distance to Mars and at the same time figured out the distance to the sun. He sent a colleague, Jean Richer, to French Guiana while he stayed in Paris. They took measurements of the position of Mars relative to background stars, and triangulated those measurements with the known distance between Paris and French Guiana. Once they had the distance to Mars, they could also calculate the distance to the sun. Since his methods were more scientific, he usually gets the credit.

New equation

With the advent of spacecraft and radar, there were now methods for making a direct measure of the distance between the Earth and the sun. The definition of AU had been "the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass, moving with a mean motion of 0.01720209895 radians per day (known as the Gaussian constant)."

Along with making things unnecessarily difficult for astronomy professors, that definition actually didn't jibe with general relativity. Using the old definition, the value of AU would change depending on an observer's location in the solar system. If an observer on Jupiter used the old definition to calculate the distance between the Earth and the sun, the measurement would vary from one made on Earth by about 1,000 meters (3,280 feet).

Moreover, the Gaussian constant depends on the mass of the sun, and because the sun loses mass as it radiates energy, the value of AU was changing along with it.

At the equator, Earth spins at just over 1,000 miles per hour. Earth makes a full spin around its axis once every 24 hours, or one day. The axis is an imaginary line through the center of the planet from the North Pole to the South Pole. Rather than straight up and down, Earth's axis is tilted at an angle of 23.5 degrees.

Why do we have day and night?
At all times, half of Earth is lighted by the sun and half is in darkness. Areas facing toward the sun experience daytime. Areas facing away from the sun experience nighttime. As the planet spins, most places on Earth cycle through day and night once every 24 hours. The North Pole and South Pole have continuous daylight or darkness depending on the time of year.

Why does Earth have seasons?
Earth has seasons because its axis is tilted. Thus, the sun's rays hit different parts of the planet more directly depending on the time of year.

From June to August, the sun's rays hit the Northern Hemisphere more directly than the Southern Hemisphere. The result is warm (summer) weather in the Northern Hemisphere and cold (winter) weather in the Southern Hemisphere.

From December to February, the sun's rays hit the Northern Hemisphere less directly than the Southern Hemisphere. The result is cold (winter) weather in the Northern Hemisphere and warm (summer) weather in the Southern Hemisphere.

From September to November, the sun shines equally on both hemispheres. The result is fall in the Northern Hemisphere and spring in the Southern Hemisphere.

The sun also shines equally on both hemispheres from March to May. The result is spring in the Northern Hemisphere and fall in the Southern Hemisphere.

Soil

What on Earth is Soil?
Here are further guidelines.

Soil Size Classification
Particle American DiameterInternational Diameter
Clay< 0.00008" / < 0.002 mm< 0.002 mm
Fine Silt0.00008 - 0.00024" / 0.002 - 0.006 mm 
Medium Silt0.00024 - 0.0008" / 0.006 - 0.02 mm0.002 - 0.05 mm
Coarse Silt0.0008 - 0.002" / 0.02 - 0.05 mm 
Very Fine Sand0.002 - 0.004" / 0.05 - 0.1 mm 
Fine Sand0.004 - 0.01" / 0.1 - 0.25 mm0.05 - 0.2 mm
Medium Sand0.01 - 0.02" / 0.25 - 0.5 mm 
Coarse Sand0.02 - 0.04" / 0.5 - 1.0 mm 0.2 - 2.0 mm
Very Coarse Sand0.04 - 0.08" / 1 - 2 mm 
Gravel/Stones> 0.08" / > 2 mm> 2 mm


What are Earth's different parts?
Air/Clouds/Temperatures The air is made up of different gases, mainly nitrogen and oxygen.
Land (mountains, valleys, flat areas. Volcanoes(gas and dust)) The land contains mountains, valleys and flat areas.
Life (plants, animals. people) Life consists of people, animals and plants. There are millions of species, or kinds of life, on Earth. Their sizes range from very tiny to very large.
Rock and metal Below Earth's surface are layers of rock and metal. Temperatures increase with depth, all the way to about 12,000 degrees Fahrenheit at Earth's inner core.
Water The water includes oceans, lakes, rivers, streams, rain, snow and ice.

Earth consists of land, air, water and life. The land contains mountains, valleys and flat areas. The air is made up of different gases, mainly nitrogen and oxygen. The water includes oceans, lakes, rivers, streams, rain, snow and ice. Life consists of people, animals and plants. There are millions of species, or kinds of life, on Earth. Their sizes range from very tiny to very large.

Below Earth's surface are layers of rock and metal. Temperatures increase with depth, all the way to about 12,000 degrees Fahrenheit at Earth's inner core.

Earth's parts once were seen as largely separate from each other. But now they are viewed together as the "Earth system." Each part connects to and affects each of the other parts. For example:

Clouds in the air drop rain and snow on land.
Water gives life to plants and animals.
Volcanoes on land send gas and dust into the air.
People breathe air and drink water.
Earth system science is the study of interactions between and among Earth's different parts.
Aerospace
Air pollution
Atmospheric dynamics
Aviation
Earth Science
    Geology: Science of the Earth
    Meteorology: Science of the Atmosphere
    Oceanography: Science of the Oceans
    Astronomy: Science of the Universe
The Earth and Beyond
Atmosphere of Earth
Atmospheric pressure

What are various types of pressure?
Atmospheric pressure
Cabin pressure
Spray pressure (aerosol pressure)
Tire pressure
Water pressure
Here are further guidelines.
Air/Clouds/Temperatures
Land (mountains, valleys, flat areas. Volcanoes/gas and dust)
Life (plants, animals. people)
Rock and metal
Water

Earth’s Surface

What should you know about the surface of Earth?

Continents (in alphabetical order):
Africa
Antarctica
Asia
Australia
North America
South America

Canyons
Caves
Coastlines
Mountains
Oceans
Plateaus
Plains
Valleys

What is the highest point on Earth?
Mt. Everest (Himalayas), 8848 m or 29,028 ft

What is the lowest point on Earth?
Mariana Trench -11,033 m or -36,198 ft

Canyons
Caves
Coastlines
Mountains
Oceans
Plateaus
Plains
Valleys

Weather and climate

What is the difference between weather and climate?
Here are further guidelines.