article : Earth, Structure and Composition the Life Place

By Eric McLamb

t's kind of fascinating to look at many of Earth's characteristics and vital information all together in one place. It's even more intriguing to have information about Earth's beginnings, neighborhood, and home galaxy in the same place. And, in a kind of humorous way, it's humbling to get a clearer perspective on where our place is in this universe after all!

Rather than looking at our galaxy and the universe as extensions of Earth, this new ecology.com feature lets us look at our planet a little bit differently, more like Earth as a part of the grand design and evolution of the universe. It's the world we live in, the place we all call home. As you start reading through the information and numerous links, you will have at least a better understanding of what and where "here" is and how we are all connected.

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Earth at a Glance: Fast Facts

Earth is located in the outer edge of our galaxy, called the Milky Way, about 28,000 light years from the galactic center. It is part of a Solar System that includes eight other known planets, and 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)

Age: About 4.5 Billion Years Old

Location: In the Solar System, on the outer edge of the Milky Way, about 28,000 light years from the galactic center (Source: European Space Agency). It takes the solar system 225 million years to make one full trip around the Milky Way.

Closest Major Galaxy: Andromeda, about 2.3 million light years away.

Age of the Milky Way: 16 billion years.

Home System: Solar System (One Sun)

Earth's Sun: A medium sized, yellow star. Scientists call it a G2 star. It is the largest object in the solar system and contains 99.8 percent of the solar system's mass. It is located in the center of the solar system.

Distance from the Sun (average): About 93.1 million miles (also one Astronomical Unit or AU). It is the third planet from the Sun.

Farthest Distance from the Sun: 94.5 million miles.

Closest Distance to the Sun: 91.4 million miles.

Speed through Space (around the sun): 18.4 miles per second or about 67,000 miles per hour.

Solar Orbit: It takes Earth 365.2422 days to orbit the sun. This is the basis for the year.

Rotational Speed: About 1,070 miles per hour at the equator.

Rotational Time: It takes the Earth 23 hours, 56 minutes and four (4) seconds to make one complete 360° rotation.

Rotational Tilt: 23.5° on its axis, a straight line through the planet from the North Pole to the South Pole. The tilt is in relation to Earth's near circular orbit around the sun.

Gravitational Pull: One Earth Unit. This measurement is relative to other objects in the universe. Earth's gravity is the force that pulls objects toward the center of the Earth and is measured by the Earth's mass. Gravity is what gives objects their weight. Without gravity, the Earth's spin would fling everything on the planet out into space! See Earth's Weight (Mass), below.

Atmospheric Pressure: 14.7 pounds per square inch at sea level. This is the measure of force exerted on objects by the weight of the air. Many times gravity and atmospheric pressure are considered one and the same thing. Actually, they are not! In fact, it is the Earth's gravitational pull on the atmosphere that gives weight to the atmosphere. The atmospheric pressure decreases above sea level, and it increases below sea level.

Earth's Weight (Mass): 5.972 sextillion (1,000 trillion) metric tons. That's 5,972,000,000,000,000,000,000 tons! Actually, scientists prefer to refer to this measurement as the Earth's mass instead of weight since weight is the result of Earth's gravitational pull on another object. And the Earth cannot pull on itself! As the Earth orbits the Sun, it is weightless. If the Earth were placed on the Sun, it would weigh more than if it were placed on Jupiter, the largest planet in the solar system but much smaller than the sun. Yet, Earth (or any other object for that matter) would have the same mass regardless of where it is located.

Earth's Size, Distances & Surface Features

Equatorial Diameter: 7,928 miles

Polar Diameter: 7,901 miles

Circumference: 24,907 miles

Surface Area: 197 million square miles

Mt. Everest

Highest Point: 29,028 feet above sea level, Mount Everest, formed 60 million years ago, located on the border of Tibet and Nepal in the Central Himalayas in southeast Asia.

Lowest Point (on Land): 1,320 feet below sea level, Dead Sea, located on the border between Israel and the West Bank to the west and Jordan to the east. It is so salty -- the saltiest on Earth -- that it is unable to support any type of life.

	Artist's depiction of the Chicxulub impact crater. (NASA)

Deepest Point on Earth: 35,802 feet, Mariana Trench in the Pacific Ocean. The water pressure there is over eight tons per square inch.

Largest Impact Crater: Chicxulub crater, about 125 miles wide and 7.5 miles deep, buried under several hundred meters of sediment. It is located off of Chicxulub, Mexico, on the northern coast of the Yucatan peninsula. It was created about 65 million years ago by an asteroid that collided with the Earth and subsequently caused the extinction of 70% of the world's species, including the dinosaurs. Only two other such craters in Canada (Sudbury) and South Africa (Vredefort) may be larger.

Earth's Layers: Earth is made up of four layers which comprise its surface, its interior and its atmosphere. They are:

• Atmosphere: The Earth's surface and interior are wrapped by its atmosphere. Its atmosphere is made up mostly of nitrogen and oxygen, with dust particles, clouds and microbes (living microscopic organisms) floating throughout. The atmosphere protects the Earth from harmful and lethal radiation and impact from small asteroids and other space matter, as well as it provides conditions essential for human and plant life (air, climate).

• Crust: The thinnest and coolest layer of the Earth's surface and interior. It is composed of the least dense calcium (Ca) and sodium (Na) aluminum-silicate minerals. The crust is rocky and brittle because it is relatively cold. This makes it particularly fragile during earthquakes. It is from 0-51 miles thick, and is thinnest under the oceans (from 0-6 miles).

• Mantle: The largest of the layers, it is about 1,792 miles thick.. Composed mostly of iron (Fe), magnesium (Mg), aluminum (Al), silicon (Si), and oxygen (O) silicate compounds. It is relatively flexible, unlike the crust, so it flows instead of fracturing.

• Core: Consists of two layers - inner (solid) and outer (molten). Mostly iron with some nickel (Ni), the core layers total about 2,166 miles thick. Its temperature is estimated at 5-9,000°F.

  ~ Outer Core - So hot that it is molten, with about 10% sulfur, about 1,410 miles thick. It is 98% responsible for producing Earth's magnetic field as it spins around the solid inner core.

  ~ Inner Core - Under such pressure that it remains solid, about 756 miles thick.

Earth's Vital Systems & Elements

• Surface Data: 70% covered by water, with the remaining 30% composed of the seven continental land masses.

• 	Atlantic Ocean

  Water Composition: 97% salt water, 3% fresh water (only .3% of all water is usable by humans).

• Total Water Supply: About 326 million cubic miles.
  

~ Oceans: 317 million cubic miles

~ Ice Caps, glaciers: Seven (7) million cubic miles

~ Ground water: Two (2) million cubic miles.

~ Fresh Water Lakes: 30,000 cubic miles

~ Inland Seas: 25,000 cubic miles

~ Soil Moisture: 16,000 cubic miles

~ Atmosphere: 3,100 cubic miles

~ Rivers: 300 cubic miles (Almost all of humans' drinking water comes from rivers.)

• Air Composition: 78% nitrogen, 21% oxygen, 1% other content (including greenhouse gases). The element Argon makes up about 93% of the other content, with carbon dioxide - the primary greenhouse gas, accounting for a little over 3%. Argon is an odorless and inert (inactive) gas that is commonly used in incandescent and fluorescent light bulbs to protect the filament.

• Greenhouse Effect: Vital to maintaining Earth's climate and life-sustaining warmth. 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 increasingly from human-caused pollution. The increase of carbon dioxide gases in the atmosphere is believed to have caused the Earth's average temperature to rise from 60°F to 61°F in the last few decades.

• Earth's Chemical Composition:

  ~ Oxygen: 46.6 %

  ~ Silicon: 27.7%

  ~ Aluminum: 8.1%

  ~ Iron: 5%

  ~ Calcium: 3.6%

  ~ Sodium: 2.8%

  ~ Potassium: 2.6%

  ~ Magnesium: 2.1%

  ~ Other: 1.5%
  (Source: US Geologic Survey)

• Average Surface Temperature: 61°F.

• Coldest Temperature (on average): -60°F (-45°F to -97°F), in Antarctica.

• Hottest Temperature (on average): 130°F, in the Sahara Desert, Africa.

• Coldest Record Temperature: -128.6°F, July 31, 1983, in Vostok, Antarctica.

• Vostok, Antarctica

  Hottest Record Temperature: 136°F, September 13, 1922 in El Azizia, Libya.

• Living Species: Some scientists estimate about 10 million species of organisms (including humans) live on Earth. Estimates range from as low as two million species to as high as 100 million.

~ Classified to date: 2.1 million species.

~ Most Unclassified Species: Invertebrates (animals without a backbone), such as insects, worms, sponges, crustaceans, mollusks, spiders, etc.

~ Total Endangered or Threatened: 12,259 species of plants and animals are known to be endangered or threatened and face a high risk of extinction in the near future, according to The World Conservation Union. IUCN documented its findings in its Red List of Threatened Species published in November 2003.

Endangered: The U.S. Florida Panther, one of 1,849 species protected under the U.S. Endangered Species Act of 1973. .

The study was assembled by over 8,000 species experts throughout the world. Among their findings: A total of 762 extinctions have been recorded since the 1500s, with a number of others surviving only in artificial habitats or other special settings such as zoos. Biologists agree, however, that there are certainly hundreds if not thousands of species that have become extinct without having been discovered.
For a summary listing of these threatened species by groups, click here …

The US Fish & Wildlife Service (USFW) lists 1,849 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 Federal list of endangered and threatened wildlife and plants. See Species Information: Threatened and Endangered Animals and Plants

In addition to its 1,286 total listings, the U.S. recognizes 558 non-U.S. species, including 268 mammals, 181 birds, 79 reptiles, 11 fishes, nine amphibians, two clams, four insects, three plants and one snail. The U.S. also has 555 specific approved recovery programs, some of which cover more than one species.

To review the current US Fish & Wildlife Service's Summary of Listed Species by groups, click here…

	Amazon Rainforest

Extinct Species: 99.9 percent of all Earth's species living at one time or another have become extinct. Without extinctions, we -- humans -- would not be here. There is no known estimate of how many species of living things have become extinct today or since animals first began to appear on Earth in the Cambrian Period, some 600 million years ago. According to the World Resources Institute, 100 species become extinct every day due to tropical deforestation. It is the rain forests that contain more than half of all living things, and there are many species that we never discovered which have succumbed to extinction.

~ Most Massive Known Extinction: There are five periods of mass extinctions recognized by scientists. The most massive extinction occurred 250 million years ago at the end of the Permian Period when between 75% and 97% of Earth's species are estimated to have died out. Perhaps the most recognized mass extinction occurred 65 million years in the late Cretaceous Period when an asteroid slammed into Earth's surface, resulting in the ultimate loss of 70% of the world species, including the dinosaurs. The current period, called the Holocene, may see the greatest mass destruction of species ever due to anthropogenic or human causes.

~ Extinction Cycles: Scientists have determined that mass extinctions are a part of Earth evolution of life forms and are indicative of changes taking place within the planet. They 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.

~ Last Known Extinction: Species are becoming extinct every day.

• First Appearance of Animals: About 500-540 million years ago, in the Cambrian Period. The first fossil records of major animal groups occur during this time.

• First Appearance of Plants: Estimated to be about 700 million years ago for land plants and 1.3 Billion years ago for land fungi (Source: Penn State University). 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.

• Human Population: About 6.2 billion people, growing at a current rate of about 50 million people per year.

• Human Life Expectancy: About 80 years on average for women, 78 years on average for men. Before 1900, few people lived to the age of 70, with an average life expectancy of 47. In prehistoric times, the average life span was about 18.

• Oldest Living Single Organism: King's Holly, a 40,000 year old Tasmanian Bush. It is older than the last ice age.

• Oldest Living Things: Ancient bacteria (bacillus strain ) found 2,000 feet below the ground in New Mexico, US. They are 250 million years old.

• Oldest Multi-Cellular Animals: Sponges. They evolved over 600 million years ago and many different types live today.

• Largest Living Animal: Blue Whale

• Largest Living Land Animal: African elephant

• Smallest Living Organism: 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.

• First Animal on Earth: The amoeba.

• Evolutionary Trends -- Continental Drift, species extinctions, species evolution, Earth's rotation (slowing), climate changes, global warming, atmospheric changes, solar changes, surface changes (earthquakes, volcanoes), desertification, temperature changes, ice cap recession. Our galaxy is also moving closer to the Andromeda galaxy at a speed of 21 miles per second due to the gravitation force between them. Andromeda is the closest galaxy to Earth, about 2.3 million light years away.

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.

Solar System Companions

Moons: One (1), circles the Earth in about 27 days and eight hours. No known life. All other planets, except for Mercury and Venus, have moons. At least 91 other moons are attached to other plants in the Solar System.

Sister Planets (in order of distance from the Sun):

Inner Planets: The inner zone of planets which are comprised mostly 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 has the hottest sustained temperatures of all the planets due to the high level of carbon dioxide (a greenhouse gas) in its atmosphere.

• (Earth): The largest of the inner planets, and the only one capable of sustaining life as we know it.

• Mars: Most similar to Earth of all the planets, with polar ice caps, seasons, clouds and fog, but colder. Recently found to have underground water. Still, Mars is unable to sustain life as we know it.

Outer Planets: The gas giants, formed from icy particles and leftover gas.

• Jupiter: The largest planet, contains most of the solar system's mass not taken up by the sun.

• Saturn: The second largest planet, with its famous rings that stretch over 600 million miles from edge to edge.

• Uranus: The third largest planet, the only one of which rotates on its side.

• Neptune: Found in 1846, it is the fourth largest of the planets and the outer most of the gas giants.

• Pluto. Not a gas giant. The smallest of the planets -- smaller than Earth's moon -- it is composed of nitrogen ice and rock, and is sometimes closer to the sun than Neptune.