THE PLANET EARTH

EARTH Earth is the only planet to be

named in English. The word ‘Earth’ is Old English word for “land“

Earth belongs to the Milky Way Galaxy

Earth is the only planet to sustain life

SHAPE OF THE EARTH The study of size and shape of earth is called

geodesy. Before 500 BC, people thought that earth

was flat. But thanks to scientists like Aristotle and Pythagoras, people know that the shape of the earth is spherical. However Sir Isaac Newton showed that the earth was not a perfect sphere, but a compressed spheroid.

SHAPE OF THE EARTHThe true shape of the Earth is

called an Oblate Spheroid. – The term "Oblate" refers to its slightly oblong appearance. – The term "Spheroid" means that it is almost a sphere, but not quite. – The Earths shape is only very slightly oblate.

EARTH'S FORMATION AND EVOLUTION

Scientists think Earth was formed at roughly the same time as the sun and other planets some 4.6 billion years ago, when the solar system came from a giant, rotating cloud of gas and dust known as the solar nebula. As the nebula collapsed because of its gravity, it spun faster and flattened into a disk. Most of the material was pulled toward the center to form the sun. Other particles within the disk collided and stuck together to form ever-larger bodies, including Earth.

Scientists think Earth started off as a waterless mass of rock. Radioactive materials in the rock and increasing pressure deep within the Earth generated enough heat to melt Earth's interior, causing some chemicals to rise to the surface and form water, while others became the gases of the atmosphere. Recent evidence suggests that Earth's crust and oceans may have formed within about 200 million years after the planet had taken shape.

EARTH'S FORMATION AND EVOLUTION

The history of Earth is divided into four eons — starting with the earliest, these are the Hadean, Archean, Proterozoic and Phanerozoic. The first three eons, which together lasted nearly 4 billion years, are together known as the Precambrian. Evidence for life has been found in the Archaean about 3.8 billion years ago, but life did not become abundant until the Phanerozoic.

EARTH'S FORMATION AND EVOLUTION

The Phanerozoic is divided into three eras — starting with the earliest, these are the Paleozoic, Mesozoic, and Cenozoic.

The Paleozoic Era saw the development of many kinds of animals and plants in the seas and on land.

The Mesozoic Era was the age of dinosaurs The Cenozoic Era we are in currently is the

age of mammals.

EARTH'S FORMATION AND EVOLUTION

STRUCTURE OF THE EARTH’S INTERIOR

The structure of earth (also referred as cross–section) is divided into mainly four layers namely Crust, Mantle, Inner Core and Outer Core .

 Outermost layer of the Earth. It is also the surface of the Earth.

This comprises the continents and ocean basins and therefore it has been classified into continental crust and oceanic crust.

Continental crust averages some 25 miles (40 km) thick, although it can be thinner or thicker in some areas. Oceanic crust is usually only about 5 miles (8 km) thick.

CRUST

About 1,800 miles (2,900 km) thick. Earth's crust floats on the mantle

much as a wood floats on water, and the slow motion of rock in the mantle shuffles continents around and causes earthquakes, volcanoes, and the formation of mountain ranges.

The division between the crust and the mantle is called the Mohorovicic discontinuity, or simply the Moho.

MANTLE

Earth's core is about 4,400 miles (7,100 km) wide

Outer core- hot and liquid layer comprising mainly of Nickel and Iron (liquid).

The transition space between outer core and mantle is called Gutenberg discontinuity 

CORE

Inner core- mostly made of solid iron and has little amounts of nickel.

believed to have the extreme temperature and pressure conditions.

The transition region between outer core and inner core is called Lehmann discontinuity 

CORE

ORBITAL CHARACTERISTICS Earth spins on an imaginary

line called an axis that runs from the North Pole to the South Pole, while also orbiting the sun. It takes Earth 23.439 hours to complete a rotation on its axis, and roughly 365.26 days to complete an orbit around the sun.

Earth's orbit is not a perfect circle, but is rather an oval-shaped ellipse, like that of the orbits of all the other planets.

ORBITAL CHARACTERISTICS

ORBIT & ROTATIONSome statistics about Earth, according to NASA: Average distance from the sun: 92,956,050 miles (149,598,262 km) Perihelion (closest approach to the sun): 91,402,640 miles

(147,098,291 km) Aphelion (farthest distance from the sun): 94,509,460 miles

(152,098,233 km) Length of solar day (single rotation on its axis): 23.934 hours Length of year (single revolution around the sun): 365.26 days Equatorial inclination to orbit: 23.4393 degrees

MOTIONS OF THE EARTH Rotation-  rotation of the planet Earth around its own axis The earth rotates on its axis from west to east or counter

clockwise. The rotation of the earth results in the alternation of day and

night. Areas facing toward the sun experience daytime. Areas facing

away from the sun experience nighttime.

MOTIONS OF THE EARTH

Revolution- earth’s movement around the sun

The earth revolves or goes around the sun in elliptical or oval orbit, from west to east.

It takes 365 days, 5 hours, 48 mins., and 46 seconds (365 and ¼ days).

A year with 366 days is called a leap 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.

Summer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter and also because the days are much longer than the nights during the summer. During the winter, the Sun's rays hit the Earth at an extreme angle, and the days are very short. These effects are due to the tilt of the Earth's axis.

SolsticesThe solstices are days when the Sun reaches its farthest northern and southern declinations. The winter solstice occurs on December 21 or 22 and marks the beginning of winter (this is the shortest day of the year). The summer solstice occurs on June 21 and marks the beginning of summer (this is the longest day of the year)

EquinoxesEquinoxes are days in which day and night are of equal duration. The two yearly equinoxes occur when the Sun crosses the celestial equator.The vernal equinox occurs in late March (this is the beginning of spring in the Northern Hemisphere and the beginning of fall in the Southern Hemisphere); the autumnal equinox occurs in late September (this is the beginning of fall in the Northern Hemisphere and the beginning of spring in the Southern Hemisphere).

STANDARD TIME For millennia, people have measured

time based on the position of the sun; it was noon when the sun was highest in the sky. Sundials were used well into the Middle Ages, at which time mechanical clocks began to appear. Cities would set their town clock by measuring the position of the sun, but every city would be on a slightly different time.

PHILIPPINE STANDARD TIME

was instituted through Batas Pambansa Blg. 8 (that defined the metric system), approved on 2 December 1978 and implemented on 1 January 1983. The Philippines is one of the few countries to officially and almost exclusively use the 12-hour clock in non-military situations.

LOCATING PLACES ON EARTH

The vertical lines originating from the north pole and end with the south pole are called meridians of longitude.

Parallels of latitude are marked horizontally on maps or globes, starting at the equator. These imaginary lines run east to west.

Why and How Does NASA Study Earth?NASA studies Earth to learn about how the planet changes. Earth's parts - land, air, water and life - are always changing. Some of the changes are natural and some are caused by humans. Scientists want to understand how Earth has changed in the past and how it is changing now. This information helps them predict how Earth might change in the future.

NASA studies Earth using satellites. Satellites look toward Earth from space. They take pictures of, and collect information about, all of Earth's parts. NASA satellites are especially good for observing clouds, oceans, land and ice. They also measure gases in the atmosphere, such as ozone and carbon dioxide. They measure how much energy enters and leaves Earth's atmosphere. And they monitor wildfires, volcanoes and their smoke.

Information gathered by NASA satellites helps scientists predict weather and climate. It also helps public health officials track disease and famine. It helps farmers decide when to plant crops and what kinds to plant. And it helps emergency workers respond to natural disasters.

The more people know about Earth and its current and predicted changes, the better decisions they can make.

AMAZINF FACTS ABOUT THE PLANET EARTH

Earth was originally born as a twin to the planet Theia, which was about half as wide as Earth and roughly the size of Mars. The two planets shared an orbit for several million years until they collided. Earth absorbed Theia, and the remaining debris eventually coagulated into Earth’s moon. The mass donated by Theia gave Earth the gravity necessary to sustain a substantial atmosphere.

The world's largest desert is the Sahara, it covers about one third of Africa!

Stretching out to an impressive length of 6696 kilometres (4160 miles) long, the Nile River is the longest river on earth.

Mt. Everest is the highest mountain on earth, its peak reaches 8,848 metres (29029 feet) above sea level. 

Hot Spot

The fiery award for Earth's hottest spot goes to El Azizia, Libya, where temperature records from weather stations reveal it hit 136 degrees Fahrenheit (57.8 degrees Celsius) on Setp. 13, 1922, according to NASA Earth Observatory.

Coldest Spot It may come as no surprise that the coldest place on Earth can

be found in Antarctica, but the chill factor is somewhat unbelievable. Winter temperatures there can drop below minus 100 degrees F (minus 73 degrees C). The lowest temperature ever recorded on Earth came from Russia's Vostok Station, where records show the air plunged to a bone-chilling minus 128.6 degrees F (minus 89.2 degrees C) on July 21,1983, according to the USGS.