The Earth: The Earth and the Solar System

The Solar System

It consists of:

• The Sun. 
• Eight planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. 
• Most planets have one or more satellites (the Earth has only one: the Moon)

The biosphere life on Earth: 

• The Earth is the only planet in the Solar System with life. 

Conditions that make life possible are: 

• The right distance from the Sun – Temperature is not too hot or too cold. 
• The atmosphere protects the Earth’s from the Sun’s radiation. 
• The existence of water. 

Biosphere: 

• It is an ecological system where life exists. 
• Most living things are found between 3,000 m above the sea level and 2,000 m below the sea level. 

The outer structure of the Earth: 

Atmosphere: It is the layer of gases that surrounds the planet.

It consists of: 

• Nitrogen: 78% 
• Oxygen: 21% 
• Other gases: 1% 

Hydrosphere – It is all the water that exists on the Earth (oceans and seas, rivers and lakes, sea, groundwater and water vapour) 

Lithosphere – It is the Earth’s solid outer layer (continents and submerged land).

The movement of the Earth:

Rotation and revolution: 

Rotation: 

• The Earth spins continually on its own axis. 
• It takes 24 hours to complete one rotation. 
• It causes the alternation of day and night. 

Revolution: 

• It is the movement of the Earth around the Sun in an elliptical orbit. 
• Earth takes 365 days and six hours to complete one revolution. 

As a calendar year only have 365 days, there is a leap year every four years, when we add an extra day to the month of February. The Earth is tilted so the angle of the Sun’s rays changes in each hemisphere during the year -> This causes the seasons.

At the Equator, the Sun’s rays reach the Earth vertically all year long – There is little difference between the seasons. 

Further from the Equator, seasons are reversed in the two hemispheres: 

• Summer – Sun’s rays reach one of the hemispheres almost vertically (at the same time, it is winter in the other hemisphere. 
• Spring and winter – Sun’s rays reach both hemispheres at a similar angle. 
• Solstices (21st June and 21st December): 

Sun’s rays reach vertically one of the tropics. It is summer in one hemisphere and winter in the other. Equinoxes (21st March and 23rd September): Sun’s rays reach vertically the Equator. Both hemispheres receive the same amount of light (it is autumn in one hemisphere and spring in the other).

How we represent the Earth:

Globes and maps: 

• The Earth is a geoid (is flat at the poles). 
• We can represent the Earth with: 
• Globes – They are the most accurate representations. 
• Maps: 
• They distort shapes and distances.  However, they are much more practical (provide information about small areas, countries or the whole world). 

Types of maps:

• Topographic maps – Show the main features of the natural environment (mountainous, rivers, …). 
• Thematic maps – Show information on a particular subject (climate, population, …).

The geographic coordinates:

Parallels and meridians: 

• They form a grid of imaginary lines. 
• They held us to locate exactly any point on the Earth. 
• Parallels: 
• They are circles in a east – west direction. 

• The Equator is the main parallel and it divides the Earth into two hemispheres (north and south). 
• There are 90 parallels between the Equator and each pole. 

Other important parallels are: the Artic Circle, the Tropic of Cancer, the Tropic of Capricorn and the Antarctic Circle.

Semicircles running in a north – south direction from the North Pole to the South Pole. 

• The Greenwich Meridian is the main meridian and it divides the Earth into two hemispheres (east and west). 
• There are 180 meridians in each hemispheres.

The coordinates:

Geographic coordinates indicate the exact location of a place on the Earth’s surface (they are measured in degrees (o), minutes (‘) and seconds (“)). 

Latitude: 

• It is the distance from a point to the Equator. 
• It can be north (N) or south (S). 
• Its values go from 0o (at the Equator) to 90o (at the Poles). 

Longitude: 

• It is the distance from a point to the Greenwich Meridian. 
• It can be east (E) or west (W). 
• It values go from 0o (at the Greenwich Meridian) to 180o. 

Scale on the map

Map scale: 

• It indicates the difference between the size of something on a map and its size in the real world. 
• There are two different ways to indicate the scale on a map: 
• Numeric scale – There are three ways: 

1 1/200,000 1:200,000 200,000 

• Graphic scale (bar scale) 

The Time Zones

Time zones were created to make the time around the world correspond to the position of the Sun. 

• Time zones are measured from the Greenwich Meridian and the Earth is divided into 24 time zones: 
• If we travel to the east, we have to move the clock by one hour if we change of time zone. 
• Equally, if we travel to the west, we have to move the clock back by one hour if we change of time zone. 

Normally, it is the same time everywhere inside a time zone – However, time zones can be influenced by political factors.

Next: «The Earth’s relief. The Earth’s crust. Structure of the Earth. Social Sciences» click here.