science / form 1 / chapter 9 / earth
 the system and structure of the earth
THE EARTH SYSTEM: consists of four main components, that are interconnected, namely atmosphere,
biosphere, hydrosphere and geosphere.
atmospheric stratification
atmosphere
earth’s atmosphere consists of 5 layers, each with it’s
respective roles
• air zone covering the earth's surface.
hydrosphere
• water zone that includes rivers, lakes, seas and
also water trapped as ice, underground water
and water vapour in the atmosphere.
geosphere
• rock and soil on the earth's surface.
biosphere
• life zone consists of a variety of life such as
humans, animals, plants and microorganisms.
-
EXOSPHERE LAYER (480KM AND ABOVE):
contains light gases such as helium and hydrogen.
air becomes thinner towards space.
communications satellites orbiting earth in this
layer allow phone calls and television broadcasts.
THERMOSPHERE LAYER (80 – 480KM):
also known as the ionosphere because it contains
ions that can reflect radio waves.
aurora, a stream of colourful lights resulting from
reactions of charged particles with earth’s magnetic field
and atmospheric gases occurs here.
MESOSPHERE LAYER (850 – 80KM):
burning and destruction of meteorites occur in this layer.
STRATOSPHERE LAYER (13 – 50KM):
- suitable and stable for aircraft flights.
- contains the ozone layer that contains ozone gas which absorb harmful ultraviolet rays from sunlight.
- the ozone layer depletes when chlorofluorocarbons (CFCs) released from pesticides, refrigerators, and airconditioners break down ozone molecules in the ozone layer.
TROPOSHERE LAYER (0 – 13KM):
- where living organisms breathes, wind blows and where clouds, rain and snow form.
relationship between air pressure and altitude
from troposphere to stratosphere, the altitude increases. the higher the
altitude, the lower the air pressure. the temperature also becomes lower
when altitude increases.
ocean stratification
the ocean can be divided into
different zones, from a zone
where light can penetrate to a
zone where light cannot.
SURFACE ZONE:
in this zone, the water is very shallow and light can penetrate. this makes the zone suitable as a habitat for
plants.
MIDNIGHT ZONE:
this zone has little or no light. it is difficult for plants to live at this depth but this level becomes the habitat for
large marine animals, such as giant squids and various species of sharks.
DARK ZONE:
this zone is very deep and no light can reach it. therefore, most animals in this zone have shimmering bodies or
able to glow in the dark.
distribution of water on earth
the ocean contains a lot of water. it all begins from when
seawater is evaporated by sunlight and is taken to the
mainland by clouds before it falls back as rainwater. the
water in the rivers then flow into the ocean. the water
cycle process is continuous. therefore, it is said that the
total amount of water contained in earth, on earth’s
surface and in earth’s surface atmosphere is always
constant.
earth’s layers
earth can be divided into three main layers according to its physical
properties, namely crust, mantle and core. the mantle consists of the
lithosphere, asthenosphere and mesophere. lithosphere covers the crust and
the top part of the mantle.
earth is the only home for living organisms
earth is the third planet from the sun and is the only planet suitable for life in our solar system. earth’s
temperature is not too hot or too cold compared to other planets. this is due to the earth’s position, which is
not too near or too far from the sun. the presence of water on oxygen also plays a role, since it allows earth
to host all life.
 composition of the earth
earth’s crust is formed from various types of rocks, which differ in colour, structure, texture and the way it is
formed. generally, the rocks can be categorized into three groups; igneous rocks, sedimentary rocks, and
metamorphic rocks. each type of rock forms differently and takes thousands of years to form. all rocks
contain materials known as minerals.
types and characteristics of rocks
IGNEOUS ROCK
SEDIMENTARY ROCK
- formed from the process of cooling and
freezing of magma or lava that flows out of the
mantle.
- formed by compression of deposited materials
carried by the rivers, glaciers and wind.
- contains various minerals.
the process of rock formation
- contains of many layers which are sometimes
hollow and contain fossils.
METAMORPHIC ROCK
- formed when igneous rocks or sedimentary
rocks are exposed to very high pressure or
temperature.
- usually harder than the original rocks that
formed them.
 main processes of the earth
earth’s surface is formed by two processes; exogenic process and endogenic process.
exogenic processes
i. erosion: process of eroding the earth’s
exogenic process
surface by moving agents such as water,
process that occurs on the earth’s
wind and waves.
surface.
ii. weathering: process of rock fragmentation
and decomposition or decay due to the
changes in temperature, rainwater, frosting
and microorganisms.
iii. mass and land depletion: involves soil movement from the top of a slope to below as a result of
gravitational force.
iv. transport and sedimentation: weathered or corroded materials are moved by agents such as running water,
wind, waves and glaciers. the materials will be sedimented when the velocity of the agents decreases.
endogenic processes
i. mantle convenction process: the high temperature in the mantle and
endogenic process
the earth and the core of the earth produces convenction currents in
process that is caused
the asthenosphere layer. these currents are able to move earth’s crust.
by forces from within
ii. earth’s crust movement (plate tectonics): according to the theory of
in the earth and forms
plate tectonics, the earth’s crust is divided into into several pieces of
plates. these plates constantly move resulting in collision and
and changes the earth.
divergence which produce various landforms on earth and continental
drifts.
iii. magma activity: a volcano is a vent on the earth’s crust that allows
molten and hot magma to flow out through it in a strong eruption. the erupted materials accumalate
around the slope of the vent and form volcanic cones.
 geohazard phenomena
consequences of the endogenic process are occurance of geohazards such as; earthquakes, landslides,
tsunamis, volcanism, global warming, sinkhole, quicksand and acid rain. geohazards pose a great impact on
the earth. they cause loss of life, diseases, starvation and damage to properties.
 age of earth
the age of earth is estimated to be 4.5 billion years based on meteorites obtained. earth has gone through
various stages of periods, which have changed or shaped the earth’s landscape. geologists define a long
period of time as an era. each era is divided into several periods.
fossils
fossils are earth’s materials such as plants, animals
and insects which have been submerged and buried
for a very long period of time. fossils have
importances to current scientific development. fossil
records can provide information about how animals
and plants species on earth have evolved over
milllions of years. fossil records can also provide
information about species that have gone extinct.
 earth’s resources and applied geology
surface water and underground water
surface water is found on the surface of earth. examples of surface water include seas, ponds and rivers.
surface water can be polluted by waste materials from industrial and housing areas. excessive fertilisers and
pesticides from agricultural areas also pollute river water. aside from surface water, there is underground
water. underground water or aquifer fills up the empty spaces between soil particles and the layers of
permeable rocks. leaching of chemical fertilisers and pesticides in agriculture exposes underground water to
the risk of pollution. chemicals from industrial and domestic waste in landfills carry the risk of polluting
underground water.
economic minerals
economic minerals in the earth consist of metallic minerals, non metallic minerals and rare earth minerals.
examples of metallic minerals are iron ore, tin and gold while examples of non-metallic minerals are coal and
petroleum. rare earth minerals consist of one or more than one of 17 rare earth elements found inside earth’s
crust. even though almost all rare earth minerals can be found in abundance, it is however not easy to
separate them as they exist together with other rare earth elements. because of the rare minerals’ unique
properties, they are very important in modern technology. they are used in computers, dvds, communication
devices, television and others. therefore, technology based on rare earth minerals is very important to the
development of the economy of the country and world in general.
formation of coal, petroleum and natural gas
petroleum and coal are used as fuel. how are they formed?
millions of years ago,
plants died naturally.
dead land organisms were buried
underground and dead marine
animals sank into the seabed.
the remains were
buried under layers
of sediment and
mud.
after millions of years, the dead
organisms became more
embedded into the earth below
thick layers of stone and mud.
under high pressure
and heat, fossil of
plants turned slowly
into coal.
thorugh the action of bacteria,
partial decomposition occured in a
state of oxygen shortage. the
continuos decompostion by
bacteria under high temperature
and pressure finally produced
petroleum and natural gas.
hydrothermal process
hot springs have their water hot. this is because the water is heated naturally from the earth. this is known as
the hydrothermal process.
negative effects of unplanned human activities
human activities that are not well planned pose a negative threat to all living things. Deforestation can cause
erosion and the extinction of flora and fauna. unplanned agriculture can cause flash floods. insutrialisation
plays a part in water, air, thermal and sound pollution. open burning contributes to global warming.