Planets can be categorized based on their composition. These include:

1. Terrestrial or Rocky Planets: They are mercury, venus, earth and mars. They are called terrestrial or rocky planets for the following reasons:

• They have a rocky and compact surface.

• They have no rings around them.

• They have a few natural satellites.

• They rotate slowly around their axis.

 

2. Gas or Jovian Planets: They include jupiter, saturn, uranus and neptune. They have the following features:

• They are called jovian planets because they are bigger in size when compared to earth.

• They are composed mainly of hydrogen and helium gas, hence the name 'gas planets' or 'gas giants'.

• They rotate rapidly.

• They have many satellites.

• They have rings around them.

Please read more on the classification of planets here.

The following rules are required for a body to become classified (or regarded) as a planet:

• It must orbit the sun.

• It does not orbit another planet. This means that it must not be a satellite.

• It must have sufficient mass which accounts for its self-gravity.

• It must assume a nearly round shape.

Please read on the planets of the solar system here.

Earth's atmosphere is extremely important for the survival of all its inhabitants. As a student, it is important you comprehend how the above functions of the atmosphere support life. The explanations below give credence to this fact.

When one moves further away from earth, the atmosphere becomes thinner until it disappears into the outer space. There is no atmosphere in space. For this reason, astronauts will always wear a spacesuit while carrying along their oxygen gas masks and canisters when in space.

People living on very high altitudes will likely experience a reduced amount of oxygen in the atmosphere. Such people survive because their bodily organs become adapted to survive in such conditions.

On mountain everest for instance, mountain climbers will need to carry oxygen canisters because lesser amount of oxygen is present on this mountain.

Please read more on the functions of the atmosphere here

The interface forming the boundary between two atmospheric layers are always named with a 'pause' at its end; for instance;

• Tropopause: This is the interface or boundary between the troposphere and stratosphere.

• Stratopause: Interface between the stratosphere and mesosphere.

• Mesopause: Interface between the mesosphere and ionosphere.

• Ionopause: Interface between the ionosphere and thermosphere.

The atmosphere surrounding the earth is layered. Each layer has its own characteristics although the boundaries between them are not clearly defined.

The image below shows the different layers of the atmosphere:

Please read more on the layers of the atmosphere here.

The average distance between the earth and the sun is about 149.6 million kilometers. It will take the earth 365 one-quarter days (or 1 year) to make a complete orbit (or revolve) round the sun. This process is termed the revolution of the earth.

The revolution of the earth is responsible for the seasonal changes we experience here (on earth). In Nigeria and Africa at large, these are the rainy and dry seasons. In Europe, these are spring, summer, autumn and winter seasons. Similarly, the United States of America have got the spring, summer, fall and winter seasons respectively.

The solar system is defined as a system comprising the sun, all the planets that revolve around it including their moons, the comets, meteoroids, asteroids and interplanetary medium.

In summary, the solar system comprises of the followings:

• Sun

• Stars

• Planets

• Moons or Satellites

• Comets

• Meteoroids

• Asteroids

• Interplanetary Medium (IPM)

Please read more on the solar system here

The atmosphere consists of gases that surround the entire surface of the spherical shaped earth. The compositions of these gases are as follows:

• Nitrogen (N₂): 78.09%
• Oxygen (O₂): 20.95%
• Argon (Ar): 0.93%
• Carbon(IV)oxide (CO₂): 0.036%
• Neon (Ne): 0.002%
• Krypto (Kr): 0.001%
• Helium (He): 0.0005%
• Xenon (Xe): 0.00009%
• Hydrogen (H₂): 0.00005%
• Water Vapour: Variable

All of these gases (listed above) make up the atmosphere and are generally called air.

Please read more on the atmosphere and it's composition here

Human Geography focuses on the study of human beings, their origin, race, and how they are affected by the earth.

Human geography can be divided into the following branches:

• Economic Geography: This aspect of human geography looks into the distribution of goods and services. Distribution of wealth across the globe is also considered here.

  Instances of economic geography include a study or research done on the richest nations on earth. During thus research, the processes accounting for their wealth are ascertained.




• Religious Geography: It studies the origin and spread of religious groups including their beliefs.

  Instances of religious geography include the study of the Christian or Islamic religion as seen in documentaries.




• Medical Geography: It studies the processes and events that bring about diseases and epidemics with regards to their geographical location, origin and distribution.

  As an instance, you may have heard about the geographical study and distribution of the disease 'COVID-19'. (Coronavirus is a case study here).

  Please read more on the branches of human geography here.

We have 3 main types or classes of rock based on how they are formed. These are:

1. Igneous Rock

 

2. Sedimentary Rock

 

3. Metamorphic Rock

Igneous rocks are formed when molten substances below the earth surface cools down and solidifies. These molten substances are called magma or lava. Magma can be derived from melting of existing rocks on the earth crust.

The solidification of molten magma into igneous rock may be below the earth's surface (intrusive) or on the earth's surface (extrusive), giving rise to the two types of igneous rock.

• Intrusive Igneous Rock: These are igneous rocks that crystallizes below the earth’s surface. They generally cool slowly during the process of solidification and tend to produce large crystals.

  Intrusive Igneous Rocks are also referred to as plutonic igneous rocks. Examples are gabbro, granite and pegmatite.

• Extrusive Igneous Rock: They are igneous rocks that form when molten magma erupts on top of the earth's surface. They cool down and solidify quickly, producing small crystals in the process. Sometimes, the molten magma cools so quickly, allowing no time for crystals to grow. This rapid cooling results in the formation of an amorphous glass.

  Extrusive Igneous Rocks are also referred to as volcanic igneous rocks. Examples are basalt, rhyolite and scoria.

Sedimentary rocks amount to about 76% of the earth's surface. They can be formed in different ways. These are:

• By the deposition of the weathered remains of pre-existing rocks and their subsequent transportation and deposition. Sedimentary rocks formed in this way are known as clastic sedimentary rock.

• By the accumulation and lithification of sediment or detrital rock.

• By their precipitation from solution. Sedimentary rocks formed in this way are known as chemical sedimentary rock.

• As a result of biogenic activities. Sedimentary rocks formed in this way are known as organic sedimentary rock.

Please read more on types of rocks here

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