Notes

Earth, the third planet from the Sun, is the only planet in the solar
system to have just the right conditions for life as we know it to exist.
These planetary characteristics, including the distance from the Sun,
the presence of an atmosphere and magnetic field, and the existence
of water, make Earth a one-of-a-kind planet.


2 Located 93 million miles away from the Sun, Earth is ideally placed
in the solar system to create the perfect temperature range to
support life. If Earth were any closer to the Sun, the temperatures
would rise. Similarly, if Earth were positioned farther away from the
Sun, average temperatures would be too cold to support life as we know it.


3 Another unique condition that allows life to thrive on Earth is the presence of the atmosphere
and its composition. In order for a planet to have an atmosphere, there has to be a gravitational
force strong enough to hold it in place. Not all planets in the solar system have an atmosphere,
let alone one that could support life. The atmosphere, all of the air and gases that surround
Earth, rises 600 kilometers above Earth's surface into space. This mixture of air and gas is
composed of 78% nitrogen, 21% oxygen, and 1% argon and carbon dioxide. Having these
gases in these amounts present in the atmosphere not only helps to keep the temperature
stable and cool, but it also provides us with the oxygen that most life forms need.


4 Extending just outside of the atmosphere is another interesting feature that allows the survival
of life on Earth: its magnetic field. Earth's magnetic field can be envisioned as a giant
protective bubble that shields Earth from harmful solar particles that stream from the Sun. Life
would simply not be possible without this protection.


5 The fourth and final characteristic that allows life to exist on Earth is the presence of water, a
necessity for all living things. In all the solar system, Earth is the only planet that possesses
liquid water. In fact, three-fourths of Earth is covered in water. The oceans help Earth maintain
stable temperatures, in much the same way as the atmosphere does. Here on Earth, water can
exist in all three states of matter: it can be a solid in the form of ice, a liquid in the form of water,
or a gas in the form of water vapor.


6 With the combination of the location of Earth, the presence of an atmosphere and magnetic
field, and the availability of liquid water, conditions for life are exactly perfect. Suitability for life
makes Earth the most interesting and unique planet in the solar system.