Take a Look at Earth

For you and me, the planet Earth is our whole, wide world. But to scientists, it is just a speck in the big picture of our galaxy, the Milky Way. Imagine the Milky Way as a great big tub of candy, filled with big jaw breakers, M&Ms, smaller gum balls and candy sprinkles.

Earth would be one of the small gumballs. Even though Earth is small in comparison to some of the other planets, we are all connected in the big bowl in the sky. Life on Earth is constantly changing. Some of the facts below stay static, or the same. Some, like the number of endangered species, change every day. So if you have questions about the numbers and facts, check out the links in the lists. You will be able to find out if anything has changed that you need to know about.

Earth is located in the outer edge of our galaxy, called the Milky Way. It is about 28,000 light years from the galactic center and is part of a Solar System that includes seven other known planets. Earth is the only known planet with the ability to sustain life as we know it. The Milky Way is one of billions of spiral galaxies in the universe. (Image: NASA, Galaxy M83, similar size and shape to the Milky Way)

Earth at a Glance: Fast Facts

Earth’s Size, Distances & Surface Features

Equatorial Diameter	7,928 miles (12,756 km)
Polar Diameter	7,901 miles (12,713 km)
Circumference	24,902 miles (40,075 km)
Surface Area	197 million square miles (510 million square kilometers)
Surface Data	70.8 percent covered by water, 29.2 percent covered by land
Mt. Everest Vredefort Crater
What is the highest point on Earth?	Mount Everest is 29,035 feet above sea level, is located on the border of Tibet and Nepal in the Central Himalayas in southeast Asia.
What is the lowest point on Land?	Approximately 1,391 feet below sea level, the Dead Sea shore is located on the border between Israel and the West Bank to the west and Jordan to the east. The water is so salty – the saltiest on Earth – that nothing can live in it.
What is the deepest point on Earth?	At 35,838 feet, Challenger Deep in the Marianas Trench in the Pacific Ocean is the deepest point. The water pressure there is over eight tons per square inch.
What is the largest Impact Crater?	Vredefort Crater in South Africa is approximately 250 kilometers in diameter and is thought to be about two billion years old.

The Earth’s Layers

Earth is made up of four layers which comprise its surface, its interior and its atmosphere
Atmosphere	The Earth is wrapped in a blanket of air called the atmosphere. The atmosphere is made up mostly of nitrogen and oxygen. It absorbs the energy from the Sun, recycles water and other chemicals.
Crust	Think of the crust being the thin coating on an M&M peanut candy. It’s holding all the good stuff inside. It’s brittle and this is where earthquakes happen. The crust is the thinnest and coolest layer of the Earth’s surface and interior. It is from 0-51 miles thick, and is thinnest under the oceans (from 0-6 miles).
Mantle	This is the M&M’s chocolate filling. It is the thickest of the layers, about 1,792 miles (2,900km) thick. The mantle is softer than the crust and when it gets really hot, you can see it as lava from a volcano.
Core	This is the peanut in the middle of the M&M! The core consists of two layers – inner (solid) and outer (molten). Scientists estimate the outer core temperature at 870 degrees Celsius and the inner core at 7,000 degrees Celsius. The outer core and inner core together cause the earth’s magnetism.
Outer Core	The outer core is so hot that it is molten, or like a liquid. It is about1370 miles (2,200 km) thick.
Inner Core	It is under such pressure that it remains solid, and is about 780 miles (1250 km) thick.

Earth’s Vital Systems & Elements

Atlantic Ocean Vostok, Antarctica Alpamayo, Peru
Water on Earth	97 percent salt water, 3 percent fresh water (only .3percent of all water is useable by humans).
Total Water on Earth	There are about 332,500,000 cubic miles (mi3) (1,386,000,000 cubic kilometers (km3)).
Oceans	About 321,000,000 mi3 (1,338,000,000 km3)
Ice Caps, Glaciers, Permanent Snow	5,773,000 cubic miles (24,064,000 cubic km)68.7 of all fresh water
Ground Water – Fresh	5,614,000 cubic miles (23,400,000 cubic km)
Ground Water – Saline	3,088,000 cubic miles (12,870,000 cubic km)
Fresh Water Lakes	21,830 cubic miles (91,000 cubic km)
Saline Lakes	20,490 cubic miles (85,400 cu km)
Soil Moisture	3,959 cubic miles (16,500 cubic km)
Atmosphere	3,095 cubic miles (12,900 cubic km)
Rivers	509 cubic miles (2,120 cubic km)Almost all of humans’ drinking water comes from rivers.
Air Composition	78 percent nitrogen, 21 percent oxygen, 1 percent other content (including greenhouse gases).
Greenhouse Effect	The Sun’s heat is trapped within Earth’s atmosphere by the greenhouse gases, mostly carbon dioxide, which enters the atmosphere through the planet’s natural carbon cycling and from human-caused pollution.
Earth’s Chemical Composition	Iron: 32.1%Oxygen: 30.1% Silicon: 15.1% Sulfur: 2.9%Magnesium: 13.9% Nickel: 1.8%Calcium: 1.5%Aluminum: 1.4% Other: 1.2%
Average Surface Temperature	60°F.
Coldest Temperature (on average)	-60°F (-45°F to -97°F), in Vostok, Antarctica
Hottest Temperature (on average)	94°F, at Dalol (or Dallol), Ethiopia.
Coldest Record Temperature	-128.6°F, July 31, 1983, in Vostok, Antarctica.
Hottest Record Temperature	136°F, September 13, 1922 in El Azizia, Libya.

Diversity of Life on Earth

Living Species	We don’t know the exact number of living species on Earth. Scientists estimate anywhere from 5 million to 100 million species on the planet, but science has only identified about 2 million.
Species classified to date	About 2 million species
Most Unclassified Species	Invertebrates (animals without a backbone), such as insects, spiders, mollusks, sponges, flatworms, starfish, urchins, earthworms, and crustaceans.
Total Endangered or Threatened Species	The latest update (2011.1) of the IUCN Red List of Threatened Species™ shows that 17,291 species out of the 47,677 assessed species are threatened with extinction. The results reveal 21 percent of all known mammals, 30 percent of all known amphibians, 12 percent of all known birds, and 28 percent of reptiles, 37 percent of freshwater fishes, 70 percent of plants, 35 percent of invertebrates assessed so far are under threat.
At Left: The U.S. Florida Panther, one of 1,976 (August 2011) species protected under the U.S. Endangered Species Act of 1973. At Right: Amazon Rainforest
Extinct Species	We may never know how many species have become extinct. In places like the rainforest, many species have not even been found, and they may become extinct before we know about them. According to the World Resources Institute, more than 100 species become extinct every day due to tropical rainforest deforestation.
Most Massive Known Extinctions	There are five periods of mass extinctions recognized by scientists. The most massive extinction occurred 250 million years ago when between 75-97 percent of Earth’s species are estimated to have died out. The most recognized mass extinction occurred 65 million years when an asteroid slammed into Earth’s surface, resulting in the ultimate loss of 70 percent of the world species, including the dinosaurs.
Extinction Cycles	Mass extinctions are part of the evolutionary circle of life. Scientists estimate that mass extinctions take place about every 26-28 million years. At the same times, existing and new species evolve and replace or add to the current surviving species.
What was the last known extinction?	Species are becoming extinct every day.
When did animals first appear?	900 million years ago. These were soft-bodied multicellular animals. The first animals with hard parts appear in the Cambrian period from 544 to 505 million years ago.
When did plants first appear?	Estimated to be about 700 million years ago for land plants and 1.3 Billion years ago for land fungi. Plants originally evolved in the oceans before drifting to land. Before the arrival of plants, Earth was a rocky, barren land mostly covered in ice.
How many people live on Earth?	Nearly 7 billion people, growing at a current rate of about 50 million people per year.
How long do most people live?	In the United States, people live on an average of 80 years. Before 1900, people had an average life expectancy of 47. In prehistoric times, the average life span was about 18.
What are the Oldest Living Things in the world?	New discoveries change what we thought were the oldest living things. A recent discovery are ancient bacteria found 2,000 feet below the ground in New Mexico, US. They are 250 million years old.
Oldest Multi-Cellular Animals	Paleontologists believe Ediacaran fauna, early slug- and worm-like creatures that fed off microbial mats that covered the ocean floor are the oldest.
What is the largest living animal?	Blue Whale is the biggest animal on the planet. The LARGEST whale ever measured was a female weighing 78,000 lbs/171,000 kgs and measuring over 90ft./27m long. The LONGEST whale measured in at over 110ft./33m. If you laid him out on the ground, he would take up the length of nine family-sized cars!
What is the largest living land animal?	The African elephant is the largest land animal. Male elephants usually weigh about 16,500 lbs/7,425 kgs and are about 20 ft/6.1m long
Smallest Living Organisms	Some scientists consider nanobes to be the smallest living organisms. They are 20-150 billionths of a meter, and are smaller than any known bacteria, spore or other single-celled organism. The smallest of the single-celled animals is the amoeba.
African Elephant (freefoto.com) The Amoeba Nanobes
What was the first animal on earth?	Earth’s first animal was the ocean-drifting comb jelly.
Leading Environmental Issues	Global warming, deforestation (rain forests) and habitat loss, water pollution and potable fresh water, air pollution, energy and energy resources, human population growth, species protection and diversity (plant and animal), land use, food production.

Our Solar System

Planets	The International Astronomical Union recognizes a total of 13 planets — eight planets and five dwarf planets. The eight planets in our Solar System are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. An easy way to remember them is using a Mnemonic: My Very Educated Mother Just Served Us Nachos. The dwarfs are Makemake, Haumea, Ceres, Pluto and Eris.
Moons	Our one moon circles the Earth in about 27 days and eight hours. All the planets, except for Mercury and Venus, have moons. Our Solar System has a total of 169 moons. There is no known life on any of the moons.
Inner Planets	These planets are mostly made up of rock and metal.
	Mercury: The second smallest planet. Although closest to the sun, it is not the hottest planet.
	Venus: Slightly smaller than Earth, and the brightest object in the night sky after the Sun and the Moon. Venus is the hottest of all the planets, due to the high level of carbon dioxide (a greenhouse gas) in its atmosphere.
	Earth: This is our home. The largest of the inner planets, and the only one capable of sustaining life as we know it.
	Mars: Also known as the Red Planet. Mars is more like Earth than the other planets, with polar ice caps, seasons, clouds and fog, but colder. Scientists say there is water on Mars, but it is frozen, so humans can’t live ther.
Outer Planets	These are giant balls of gas, formed from icy particles and leftover gases. There are four outer planets.
	Jupiter is the largest planet in the solar system. It is so big that all the other planets in the solar system could fit inside it. Jupiter puts out twice as much heat as it absorbs from the sun.
	Saturn: The second largest planet, with its famous rings that stretch over 600 million miles from edge to edge. This planet has 62 moons.
	Uranus: The third largest planet, the only one of which rotates on its side. Uranus has 27 moons.
	Neptune: Found in 1846, it is the fourth largest of the planets and the outer most of the gas giants.
Jupiter (Courtesy: NASA) Saturn (Courtesy: NASA) Uranus (Courtesy: NASA) Neptune (Courtesy: NASA)
Dwarf Planets	“Dwarf planets” is a new category of planets, created by the Atronomical Union in 2006. These planets are too small to be real planets, and bigger than asteroids and comets.
	Ceres is the called and asteroid and a dwarf planet.
	Pluto was first called a planet but downgraded to a dwarf in 2006.
	Haumea was named for the Hawaiian goddess Haumea. She is the goddess of fertility and childbirth.
	Makemake was discovered around Easter in 2005 and was first named “Easterbunny.”
	Eris was one of the first objects to be classified as a dwarf planet. It was discovered in 2005.
Other Solar System Cohabitants	Asteroids
	Comets
	Meteoroids
	Kuiper Belt Objects
	Halley’s Comet (NASA)

Footnote to Endangered Species

For a summary listing of these threatened species by groups, click here…

The US Fish & Wildlife Service (USFW) lists 1,976 species of plants and animals as endangered or threatened under its Endangered Species Act, which was signed into law by President Richard Nixon in 1973. Before a plant or animal species can receive protection under the Endangered Species Act, it must first be placed on the http://www.fws.gov/endangered/laws-policies/index.html.

Did You Know?

• Other planets have been discovered orbiting other stars in the Milky Way, the closest being about 42 light-years away. They range in size from Earth-size to several times the mass of our own Jupiter. It is possible that some of these planets may harbor the right elements to support life.
• The massive size of Jupiter makes it a kind of body guard for our planet. Its gravitational pull is so enormous because of its size that it will attract objects flying in space away from Earth. However, as our geologic history tells us, Earth is still vulnerable to such impacts. Sixty-five million years ago, a large asteroid or comet crashed into the Earth’s surface, resulting in the extinction of about 70% of the world’s species.
• The largest height variation between the highest mountain and the deepest point in the bottom of the ocean is about 12 miles.
• The Solar System has orbited the center of the Milky Way about 21 times since it formed about 4.5 billion years ago.
• Most of Earth’s land masses are in the northern hemisphere. There is no particular reason for this, and scientists consider it a coincidence.
• The Earth’s solid iron inner core, which was discovered by seismological methods in 1936, is estimated at being roughly the size of the moon. It rotates because it is surrounded by a much larger, liquid outer core and together the two form a giant electrical motor.
• By the year 2025, Earth could lose as many as one fifth of all species known to exist today. In recent centuries, hundreds of species have disappeared. The passenger pigeon, one familiar example, was a source of food until excessive hunting and habitat loss caused its extinction in 1914.
• Earth’s atmosphere has more free oxygen today than it did when Earth formed. While the early atmosphere was mostly carbon dioxide, more than three-quarters of Earth’s atmosphere is now nitrogen, and most of the rest of it is oxygen. Chemical reactions locked much of the early carbon dioxide inside rocks, while plants produce the oxygen for our present-day atmosphere.
• The Earth’s core was formed early in the creation of the planet as heavier molten iron sank toward the center. As the planet cooled, some molten iron began to solidify to create the core, which is kept solid by enormous pressure.
• Earth’s oldest fossils date to roughly 3.5 billion years ago and consist of bacteria microfossils.
• Is Earth gaining weight? At the present rate, Earth gains about 40,000 metric tons each year from space debris that bombard our planet. Yet it loses an amount so small (atmospheric gases, etc.) as to not really warrant any serious consideration. So, will Earth’s weight gain have an impact on its orbit, relative mass (gravitational pull) or any other properties? Although 40,000 metric tons a year sounds like a huge gain, when you compare it to the immense size of Earth, it dwindles to a meager 0.000003 of one percent of the Earth’s mass. The impact is insignificant.

Other Sources of Information

• Earth from Space: Astronauts’ Views
• Timeline of the Universe
• Endangered Species
• The Nine Planets

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