All About The Earth

A Look at Earth....

In astrological terms the Earth is the third planet from Sol, the star in our solar system, one of billions of similar stars in the Milky Way, the galaxy which contains said stars and one of billions of such galaxies in the known, observable universe. As such the Earth is hardly an atom in a grain of sand on the largest of beaches, yet at one time it was thought that every other thing in the sky and beyond revolved around it. To date, Earth is unique in that it not only supports life, but civilization.

The Makeup of Earth

The Earth was formed, as were all the planets of the solar system, from material in the protoplanetary disk that surrounded the sun when it formed, some four and a half billion years ago. Working from the inside out, the Earth has a solid inner core, located 5,000 kilometres from the surface, which consists of a nickel-iron alloy. Surrounding that is a liquid outer core, which starts 3,000 kilometres from the surface, and is molten iron. Next is, 35 kilometres down, the mantle, a thick rocky area that makes up about 70 percent of the Earth's volume. Sitting on top of the mantle is the crust, atop which humanity lives.

Sitting on the crust is a feature unique in the known universe—liquid water oceans. The Earth's hydrosphere is chiefly ocean, although technically it contains all water on the Earth. The liquid water is mostly salt water, and the majority of fresh water is locked in ice, but the water is one of the key elements that allowed life to form on the planet.

Blanketing the planet is the atmosphere, which is not unique to Earth but is comprised of just the right mix of nitrogen and oxygen to both provide life, giving air to breathe and life protecting filtration. The ultra violet rays of the sun are dampened just enough in the atmosphere to prevent the temperatures on Earth from rising to the point that nothing would survive.

Earth as Reference Point

Naturally Earth's scientists use the planet as a reference point when examining the universe, drawing comparisons with what they understand of Earth and the differences and similarities found elsewhere. One such reference is the Astronomical Unit, or AU, which is how astronomers measure distance in space; one AU is equal to the distance from the Earth to the Sun, or roughly 150 million kilometres.

Final Thoughts

To look outwards, sometimes scientists look inwards. In asking the question "can life exist in different extreme conditions" astrobiologists turn to the Earth itself, where micro organisms have been found living in superheated streams of gas, for example. The Earth may one day be the launching point of a galactic civilization, but until that point it remains humanity's home and has much to teach, about itself and the universe.

Related Articles in the 'The Planets' Category...

• ISS Assembly Sequence
• Jupiter
• Mars
• Neptune
• Planet Mercury
• Planet Venus
• Planets Outside the Solar System
• Pluto
• Saturn
• Uranus