Characteristics of the Earth
Our planet Earth is a rotating sphere that orbits the Sun. The Earth's axis of rotation is at a
constant tilt with respect to its orbit around the Sun, resulting in the change of seasons. The
physical characteristics of the Earth include its size and composition. The Earth also has gravity
and magnetic force fields.
Earth's relationship with Sun
The Earth is the third planet from the Sun, with Mercury and Venus being closer. Its unique
position gives the Earth a temperate climate, allowing the chemical reactions necessary to
sustain life. But over the years, the climate has varied enough to melt the ice caps near the North
and South poles, or to cause glaciers to move south in an Ice Age.
Revolves around the Sun in an orbit
The Earth goes around the Sun in a counterclockwise orbit, taking a year or about 365 days to
make one revolution. The orbit is an ellipse, so the Sun is slightly off-center.
The Earth orbits the Sun
The average distance from the Sun is 149,597,890 kilometers (92,955,820 miles). This distance is
so great that it takes light about 8 minutes to reach the Earth from the Sun.
Spins on its axis
The Earth spins or rotates on its axis in a counterclockwise motion, as viewed from above the
North Pole. It makes one revolution in 24 hours.
The spinning of the Earth on its axis is what causes the Sun to appear to move across the sky.
The effect the apparent movement of the Sun is similar to looking out the window of a moving
car, where things outside appear to be moving past you.
Tilt affects seasons
The Earth's axis also tilts with respect to the Sun, causing the changes of the seasons. In
summer, the Earth is tilted such that the Sun falls more directly, while in winter the Sun looks
lower in the horizon and the light comes at a glancing angle. The tilt of the Earth also causes the
summer days to be longer than the nights. In winter the days are shorter and there is less light to
heat the ground.
The light from the Sun is more direct in summer than
in winter at the same latitude
The further north you go, the more the effect of the tilt of the Earth is apparent. Above the Arctic
Circle, daylight can be seen for a full 24 hours in the summer or night can be 24 hours in the
winter. That is why they call the area "the land of the midnight sun."
Moon
The Earth has only one moon, while Mars has two moons and Jupiter has 9 moons.
Physical characteristics of Earth
Physical characteristics include shape, size and composition.
Spherical in shape
Just as the Sun and Moon appear as spheres, so too is the Earth spherical in shape. To people on
Earth, the planet appears to be generally flat (not counting for hills and valleys), but in reality
the surface of the Earth has a slight curve. This can be noticed when looking out on a large lake
or the ocean and seeing a ship come up along the horizon.
Ship coming up over the horizon
The shape of the Earth has been proven by ships circling the Earth, as well as from pictures of
the Earth taken from the space vehicles.
View of Earth from space
Its shape is actually slightly flattened at the poles.
Size
The diameter of the Earth at the equator is 12,756 km (7,926 miles), and its circumference or
distance around the Earth at the equator is 40,075 km (24,901 miles).
Composition
The composition of the Earth consists of the solid and liquid portion and the atmosphere or
gaseous portion.
Solid and liquid
The percentage composition of the Earth's solid and liquid materials (by mass) is:
Element
Percentage
Iron
34.6%
Oxygen
29.5%
Silicon
15.2%
Magnesium
12.7%
Nickel
2.4%
Sulfur
1.9%
Titanium
0.05%
Oxygen is chemically combined with many substances to produce liquid and solid compounds.
Although water (H2O) is a dominant compound on Earth, Hydrogen is not listed above because of
its small mass.
Silicon Dioxide (SiO2) is sand, and that compound makes up a large portion of the Earth's mass.
Much of the Iron is in the Earth's core and is responsible for the Earth's magnetic field.
Atmosphere
Although most people think air is mainly Oxygen, the atmosphere of the Earth actually consists
of 79% Nitrogen (N2), 20% Oxygen (O2) and 1% of other gases such as Carbon Dioxide (CO2).
Force fields: The Earth has two major force fields: gravity and magnetism.
Gravity
Gravity is the force at a distance that attracts objects of mass toward each other. The force of
gravity from the Earth holds down our atmosphere, oceans and everything else.
Some planets and moons that have less gravity than Earth have lost their atmosphere because it
wasn't sufficient to hold the gas close to the surface.
When you throw a ball or shoot a bullet upward, it will slow down due to the Earth's gravity,
until it finally falls back to the ground. You would have to shoot the object at 40,248 km/hr
(25,009 mph) for it to escape the Earth's gravity and fly out into space. This is called the Earth's
Escape Velocity.
Magnetic field
The Earth is like a giant magnet with a magnetic pole near the North Pole and the opposite near
the South Pole. The north pole of a magnet seeks the North Magnetic Pole. Through the ages,
indications are that the poles switched directions. No one is sure why this happened.
The rotation of the Earth and the fact that the core of the Earth is made of iron are major factors
in creating the magnetic field.
One thing the magnetic field does is to attract charged particles that have been emitted from the
Sun. The focusing of these particles at the poles may help to prevent us from being harmed by the
high energy particles.
These particles cause the air in the upper atmosphere to glow. This is called the northern lights
(aurora borealis) or southern lights (aurora australis).
Summary
The Earth is a rotating sphere that orbits the Sun. The axis of rotation of the Earth is at a
constant tilt with respect to its orbit around the Sun, thus resulting in the change of seasons. Iron
and oxygen make up 65% of the Earth's mass. The Earth also has gravity and magnetic force
fields.
Characteristics of the Earth
Name: ___________________________
Curriculum Outcomes Addressed
• To familiarize students with the characteristics that make Earth unique.
• To nurture in students appreciation for the fact that Earth has an environment that is unique in the solar system, one whose whole is far greater than
the sum of its parts.
Answer the following questions about the Earth’s unique characteristics after reading through the
information package provided.
1. What is Earth’s position in the solar system? What is the Earth’s relationship with the Sun?
2. What causes the different Seasons throughout a year?
3. Explain Earth’s physical characteristics by giving a brief description of the following.
a. Shape:
b. Size:
c. Composition:
d. Atmosphere:
e. Force Fields:
4. What are the Earth’s two major force fields? What do these force fields do?
a.
b.
5. What property of water plays a major role in keeping the Earth’s temperature and climate
regulated? What would happen if this property of water was low?