Video Transcript
In this video, we will learn how to
describe the characteristics of Earth that are essential to supporting life.
The planet Earth is our home. Earth has a roughly spherical shape
and is one of eight planets in our solar system. Earth has five main characteristics
that are necessary to supporting life. First, the Earth is surrounded by
an atmosphere. The atmosphere is made up of
gases. The Earth also has a
hydrosphere. The hydrosphere contains water. The temperature of the Earth is
also very important in sustaining life. There are only certain temperatures
at which organisms on Earth can live. So, Earth’s temperature cannot be
too hot or too cold.
Earth, like all planets in the
solar system, experiences the force of gravity. But Earth also exerts gravity on
objects and organisms. The force of gravity keeps Earth’s
atmosphere and hydrosphere where it is. Finally, the Earth has atmospheric
pressure. The pressure exerted by Earth’s
atmosphere is suitable for living organisms. If the pressure were much lower or
higher than what it is, life might not exist.
Let’s begin by discussing what the
atmosphere is and what it is made of. The atmosphere is the layer of
gases that surrounds the Earth. The atmosphere contains gases that
are essential to life. There are four main gases in
Earth’s atmosphere. These gases are nitrogen, oxygen,
carbon dioxide, and water vapor, which is the gaseous form of water. Nitrogen and oxygen are both
elements. Nitrogen gas has the formula N2,
and oxygen gas has the formula O2. Carbon dioxide and water vapor are
compounds. The chemical formula of carbon
dioxide is CO2, and the chemical formula of water is H2O. The most abundant gas in the
atmosphere is nitrogen gas. About 78 percent of the atmosphere
is nitrogen gas.
The second most abundant gas in the
atmosphere is oxygen. Oxygen makes up about 21 percent of
the atmosphere. Only about 0.03 percent of the
atmosphere is carbon dioxide. The rest of the atmosphere is
composed of water vapor and very small amounts of other gases, such as helium. The amount of water vapor in the
atmosphere constantly changes due to processes involved in the water cycle and
weather.
Now that we know the gases that are
in Earth’s atmosphere, let’s discuss how these gases support life. Oxygen is a vital gas for many
organisms on Earth. Many organisms use oxygen for
respiration, which allows them to obtain energy from food. Oxygen is also a reactant in
combustion reactions. Having oxygen in the atmosphere
means that materials can be burned.
Nitrogen gas also plays an
important role in sustaining life on Earth. Plants use nitrogen to make
proteins and grow. Nitrogen gas in the atmosphere also
controls the rate of combustion reactions.
Finally, let’s discuss the
importance of carbon dioxide. Plants use carbon dioxide for
photosynthesis. They use carbon dioxide in the
atmosphere, water in the soil, and light energy from the Sun to make glucose. These plants are then a food source
for other organisms. Cells in humans break down sugar in
plants for energy by using oxygen.
Another way that the atmosphere
preserves life on Earth is through protection. The atmosphere protects life on
Earth from small meteors. Small meteors burn up in the
atmosphere and do not tend to reach Earth. Large meteors do not completely
burn up in the atmosphere, but they may partially burn and slow down. The atmosphere also protects life
on Earth from harmful ultraviolet radiation from the Sun. Much of this harmful UV radiation
is absorbed by the ozone layer. Gases in the atmosphere also act as
insulation. Gases, such as carbon dioxide, trap
heat and help maintain a suitable global temperature for life to exist on Earth. The gases in the atmosphere move
and flow. This movement contributes to
Earth’s weather and climate, including winds, clouds, rain, and storms.
Now let’s discuss the second
characteristic that sustains life on Earth, the hydrosphere. The hydrosphere is the total amount
of water on a planet. This includes water on the surface
of the Earth, water underground, and water vapor in the atmosphere. Water covers about 71 percent of
Earth’s surface. The rest of the surface is
land. Most of the water on the Earth, or
about 97 percent, is salt water. The remaining three percent is
fresh water. Salt water is typically found in
the oceans and seas. Fresh water tends to be found in
rivers, lakes, and in the snow at the poles. Most of the Earth’s groundwater is
also fresh water. Gravity can pull water into the
Earth, where it passes through the soil and cracks and holes in rocks and gets
trapped as groundwater.
Now that we know what the
hydrosphere is made of, let’s discuss its importance for life on Earth. Plants, animals, and humans need
water to live. As we mentioned earlier, plants use
water to carry out photosynthesis. Plants absorb water from the soil
into their roots. Water moves to the leaves where
photosynthesis takes place. Carbon dioxide, water, and light
energy are used to make sugar in the leaves.
The human body is about 60 percent
water. We need water for processes in our
body, such as digesting food and absorbing nutrients. Water in our body also helps us to
maintain a stable body temperature.
It takes a lot of energy to raise
the temperature of water, so the hydrosphere also helps to keep the temperature on
land stable too. So, land tends to not get too hot
during the day or too cold at night. Finally, the hydrosphere provides
habitat for many organisms. Over 50 percent of the organisms on
Earth live in water-based environments.
The third characteristic that helps
support life on Earth is temperature. We already know that Earth’s
temperature must remain relatively stable for life to survive. There are three main factors that
influence Earth’s overall temperature: the distance of the Earth from the Sun,
Earth’s atmosphere, and Earth’s hydrosphere. These three factors contribute to
maintaining a stable temperature on Earth for organisms to live and grow.
The fourth characteristic that
sustains life on Earth is gravity. The Earth exerts a force of gravity
on objects and organisms. This includes the atmosphere. The gases in the atmosphere around
the Earth are held in place by gravity. Gravity also holds the Earth’s
hydrosphere in place.
The last characteristic of Earth
that helps support life is atmospheric pressure. Atmospheric pressure comes from the
weight of the gases in the atmosphere. A barometer is used to measure
atmospheric pressure. A simple barometer is made from a
glass tube placed upside down into a dish holding liquid mercury. At sea level, the pressure from
Earth’s atmosphere pushes the mercury up the tube 76 centimeters. So, we say that the atmospheric
pressure of Earth is around 76 centimeters Hg. Hg is the chemical symbol of
mercury. This is a suitable atmospheric
pressure for living organisms on Earth.
Now that we’ve discussed the five
characteristics of Earth that support life, let’s learn about the inner structure of
the Earth. Although we can’t see these layers,
they have different properties and are made of different substances. They may be thick or thin, and they
may be solid or molten. The structure of the Earth can be
thought of being sort of like a hard-boiled egg. If we cut open the boiled egg, we
could easily see the different layers. There is a hard shell that is very
thin and two soft but thick layers made of different materials, the white of the egg
and the yolk.
The inner structure of the Earth
has four main layers: the crust, the mantle, the outer core, and the inner core. The crust is the outermost layer of
the Earth. It is between eight and 60
kilometers thick. The crust is made of light rocks
and particles. Below the crust is the mantle. The mantle is the thickest layer of
the Earth. It is also a rocky layer, which
means that it is composed of solid rock. But under the right conditions,
this rock can move and flow. So the mantle acts like a solid and
a liquid. The outer core is the next
layer. The outer core is around 2100
kilometers thick. The outer core is made of molten
metals. These metals are in the liquid
state because the temperature of the outer core is very high.
Finally, the innermost layer of the
Earth is the inner core. This layer is around 1350
kilometers thick. Due to very high pressures, the
inner core is completely solid. It is made up of iron and nickel
metals, which are very dense.
Now before we summarize what we’ve
learned, let’s take a look at a couple of questions.
What is the most abundant gas in
Earth’s atmosphere? (A) Helium, (B) carbon dioxide, (C)
nitrogen, (D) water vapor, (E) oxygen.
First of all, the atmosphere is the
layer of gases that surrounds Earth. Some of these gases are essential
for the survival and growth of living organisms. The four main gases in Earth’s
atmosphere are nitrogen, oxygen, carbon dioxide, and water vapor. There are also other gases in the
atmosphere, but they are in very small amounts. One of these trace gases is
helium.
In this question, we need to
determine which gas is the most abundant. In other words, we need to find out
which of the gases makes up the largest percentage of the atmosphere. Since there is a very small amount
of helium in the atmosphere, we can eliminate answer choice (A).
There is a pretty small amount of
water vapor in the atmosphere, but it changes all the time due to weather patterns
and the water cycle. Carbon dioxide only makes up about
0.03 percent of the atmosphere. Since there are such small amounts
of carbon dioxide and water vapor in the atmosphere, we can eliminate answer choices
(B) and (D). Oxygen gas makes up 21 percent of
the atmosphere, and nitrogen gas makes up 78 percent. Nitrogen makes up the largest
percentage of the atmosphere, so it must be the correct answer. In conclusion, the most abundant
gas in Earth’s atmosphere is nitrogen, or answer choice (C).
In which of the following are the
layers of Earth’s structure placed in the correct order? (A) Crust, mantle, outer core,
inner core. (B) Mantle, crust, inner core,
outer core. (C) Crust, mantle, inner core,
outer core. (D) Crust, outer core, inner core,
mantle. (E) Mantle, crust, outer core,
inner core.
Earth’s inner structure is divided
into four main layers. The outermost layer is the
crust. The crust is the thinnest layer and
is around eight to 60 kilometers thick. The layer underneath the crust is
the mantle. On average, the mantle is about
2885 kilometers thick and is the thickest layer. Underneath the mantle, the next
layer is the outer core. The outer core is around 2100
kilometers thick. Finally, the innermost layer of the
Earth is the inner core. The inner core is about 1350
kilometers thick.
So, in which of the following are
the layers of Earth’s structure placed in the correct order? That’s answer choice (A): crust,
mantle, outer core, inner core.
Now, let’s summarize our learning
with some key points. The five characteristics of Earth
necessary to sustain life are the atmosphere, the hydrosphere, temperature, gravity,
and atmospheric pressure.
The atmosphere is composed of
nitrogen, oxygen, carbon dioxide, and water vapor, as well as small amounts of other
gases. Nitrogen is the most abundant gas
in the atmosphere and makes up 78 percent of the atmosphere. Oxygen gas makes up 21 percent of
the atmosphere. The hydrosphere is the total amount
of water on the planet. Land covers 29 percent of Earth’s
surface and water covers 71 percent. 97 percent of Earth’s water is salt
water and only three percent is fresh water. Gravity keeps the atmosphere,
hydrosphere, objects, and organisms on or near the planet. The structure of the Earth is
composed of four layers: the crust, mantle, outer core, and inner core. The outer core is molten and all
the other layers are solid.
