Science notes, chapter 9

Earth

Textbook Science Form 1 (DLP), pages 254–277

By the end of this chapter you can

Describe the four components of the Earth system, the layers of the atmosphere and ocean, the water cycle and the Earth's layers, and explain why Earth supports life (9.1)
Describe igneous, sedimentary and metamorphic rocks and explain how they form in the rock cycle (9.2)
Explain exogenic and endogenic processes that change the Earth's surface (9.3)
Describe geohazards, their impact, and the technology used to give early warnings (9.4)
Describe the age of the Earth, the geological time scale and the importance of fossils (9.5)
Explain surface and underground water, economic minerals, the formation of coal and petroleum, the hydrothermal process and the effects of unplanned human activities (9.6)

9.1The System and Structure of the Earth

Earth is spherical, even though the horizon looks flat. The voyage of Ferdinand Magellan's crew around the world (1519–1522) proved it. His translator was a Malay man from Malacca, Panglima Awang.

The Earth system has four main components that are connected to one another:
Atmosphere — the air zone covering the Earth's surface.
Hydrosphere — the water zone: rivers, lakes, seas, ice, underground water and water vapour in the air.
Geosphere — the rock and soil zone on the Earth's surface.
Biosphere — the life zone: humans, animals, plants and microorganisms.

Photographs of the hydrosphere, atmosphere, geosphere and biosphere around the Earth — The four components of the Earth system.

Textbook Photograph 9.1, p. 256.

Layers of the atmosphere

The atmosphere has five layers. Learn them from the ground upwards: Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere.

Layer	Height	What happens there
Troposphere	0 – 13 km	Living things breathe; wind blows; clouds, rain and snow form (the weather layer)
Stratosphere	13 – 50 km	Stable layer for aircraft flights; contains the ozone layer, which absorbs harmful ultraviolet (UV) rays
Mesosphere	50 – 80 km	Meteorites burn up and are destroyed
Thermosphere	80 – 480 km	Also called the ionosphere — its ions reflect radio waves; the aurora (coloured lights) happens here
Exosphere	480 km and above	Light gases (helium, hydrogen); air becomes thinner towards space; communication satellites orbit here

The five layers of the atmosphere with a satellite, aurora, meteor, aeroplane and hot-air balloon — Atmospheric stratification.

Textbook Figure 9.1, p. 257.

Ozone depletion: chlorofluorocarbons (CFCs) released from pesticides, refrigerators and air-conditioners break down ozone molecules. A thinner ozone layer lets more UV rays reach us.

Altitude and air pressure. The higher you go, the lower the air pressure and the lower the temperature. That is why mountain climbers feel cold and find it harder to breathe. Air pressure at sea level is about 101 325 Pa.

Graph: altitude against air pressure; pressure falls as altitude rises — As altitude increases, air pressure decreases.

Textbook Figure 9.2, p. 258.

Zones of the ocean

The ocean is divided into zones by how much light reaches them.

Zone	Depth	Light	Life
Surface zone	0 – about 200 m	Light can get through	Plants can live here (they need light)
Midnight zone	about 200 – 1500 m	Little or no light	Hard for plants; large animals such as giant squids and whales
Dark zone	below about 1500 m	No light at all	Most animals have shimmering bodies or glow in the dark

Ocean zones: surface zone, midnight zone and dark zone with depth scale — Ocean stratification.

Textbook Figure 9.3, p. 258.

The water cycle

The Sun evaporates seawater. The water vapour condenses into clouds, which are carried over land and fall as rain. Rainwater flows over the surface into rivers, or seeps into the ground as underground water, and finally returns to the ocean. Because the cycle never stops, the total amount of water on Earth stays constant.

Textbook Figure 9.4, p. 259.

The Earth's layers

Earth has three main layers based on its physical properties: the crust, the mantle and the core (outer core and inner core). The mantle is made up of the lithosphere, asthenosphere and mesosphere. The lithosphere covers the crust and the top part of the mantle.

Cut-away Earth showing crust, mantle, outer core and inner core — The Earth's main layers, from the outside in: crust → mantle → outer core → inner core.

Textbook Figure 9.5, p. 260.

Why only Earth supports life

Earth is the third planet from the Sun and the only planet in our Solar System known to support life, because:

its temperature is not too hot and not too cold — it is not too near and not too far from the Sun;
it has water;
it has oxygen.

A fish catches its prey using light. In which zone of the ocean does it live? Why?

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The surface zone — it is the only zone that light can reach, so the fish can see its prey.

9.2Composition of the Earth

The Earth's crust is made of rocks. All rocks contain natural materials called minerals. Rocks differ in colour, structure, texture and how they formed, and they take thousands of years to form.

Igneous rock
Forms when magma or lava cools and freezes. Contains various minerals.

Sedimentary rock
Forms when materials deposited by rivers, glaciers and wind are compressed. Has layers, is sometimes hollow and may contain fossils.

Metamorphic rock
Forms when igneous or sedimentary rock is exposed to very high pressure and temperature. Usually harder than the original rock.

Rock photographs: textbook Table 9.1, p. 262.

The rock cycle

Textbook Figure 9.6, p. 262.

Magma cools and freezes → igneous rock.
Rock is uplifted to the surface, then broken up by weathering and carried away by erosion.
The eroded materials settle (sedimentation) and are compressed → sedimentary rock.
Heat and pressure change igneous or sedimentary rock → metamorphic rock.
Deep underground, rock melts back into magma, and the cycle starts again.

Why no fossils in igneous rock? It forms from very hot magma, where no living thing can survive — so there is nothing left to fossilise.

Why are metamorphic rocks harder than igneous and sedimentary rocks?

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They are formed under very high pressure and temperature, which squeezes and changes the original rock.

9.3Main Processes of the Earth

Two kinds of process shape the Earth's surface.

Exogenic process — a process that happens on the Earth's surface.
Endogenic process — a process caused by forces from within the Earth.

Exogenic processes

Process	What it is
Weathering	Rocks break up and decay because of changes in temperature, rainwater, frost and microorganisms
Erosion	The surface is worn away by moving agents: water, wind and waves
Mass and land depletion	Soil moves down a slope because of gravity
Transport and sedimentation	Running water, wind, waves and glaciers carry weathered material; it settles when the agent slows down

Endogenic processes

Mantle convection
Heat from the mantle and core makes convection currents in the asthenosphere. These currents move the crust.

Two plates of the Earth's crust moving, with arrows showing their directions

Plate tectonics
The crust is split into plates that keep moving. They collide or move apart (divergence), forming landforms and causing continental drift.

Magma activity
A volcano is a vent in the crust. Hot magma erupts through it, and the material piles up to form a volcanic cone.

Textbook Figures 9.7 and 9.8, pp. 263–264.

Do not mix up weathering and erosion. Weathering breaks rock up where it is; erosion wears it away and moves it, using water, wind or waves.

Is the eruption of a volcano an exogenic or an endogenic process? Explain.

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Endogenic — it is caused by magma, a force from within the Earth.

9.4Geohazard Phenomena

Geohazards are natural events related to the Earth that can harm people and property, for example earthquakes, landslides, tsunamis, volcanism, sinkholes, global warming, quicksand (in wetlands) and acid rain (in industrial areas).

Tsunami

Volcanism

Landslide

Textbook Photograph 9.3, p. 265.

Technology for early warnings

A landslide detector is placed on hill slopes. When the slope moves, the gravel rubs and makes sound that an acoustic sensor picks up.
A tsunami detector is placed at the shoreline and sends early warnings of a tsunami via satellite.
A seismograph detects earthquake vibrations.

Landslide detector with transducer, acoustic sensor, steel waveguide and gravel backfill — The device to detect landslides.

Textbook Figure 9.10, p. 266.

Impact of geohazards

Geohazards can cause loss of life, disease, starvation and damage to property. Examples in Malaysia: the 2004 tsunami (43 Malaysians killed), the 2015 Mount Kinabalu earthquake (19 killed) and mudslides in Cameron Highlands. We should sympathise with and help disaster victims.

State two devices used to give early warnings of geohazards.

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Any two: landslide detector (acoustic sensor), tsunami detector, seismograph.

9.5Age of the Earth

The Earth is about 4.5 billion years (4500 million years) old. Scientists estimated this from meteorites.

The geological time scale divides Earth's history into long periods called eras. Each era is divided into several periods.

Era (oldest at the bottom)	Main life
Cenozoic — we live in this era	Mammals; humans
Mesozoic	Dinosaurs; first flowering plants
Paleozoic	Fish, insects, early land plants
Precambrian	Bacteria, protozoa, seaweed, jellyfish

Eras: textbook Figure 9.11, p. 268 (M.Y. = million years).

Spiral timeline showing when different organisms appeared — Organisms on Earth since 5000 million years ago. Read it clockwise from "Origin of Earth".

Textbook Figure 9.13, p. 269.

Fossils are the remains of plants, animals and insects that were buried for a very long time. The word comes from the Latin fossilis, "obtained from digging".

Why fossils matter: they show how plant and animal species have evolved over millions of years, and they tell us about species that have become extinct. In Malaysia, dinosaur fossils were found for the first time in Pahang.

Using the timeline, which appeared first: insects or flowering plants? When did fish first appear?

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Insects appeared before flowering plants. Fish first appeared about 500 million years ago.

9.6Earth's Resources and Applied Geology

Surface water and underground water

	Surface water	Underground water
What	Water on the Earth's surface: seas, ponds, rivers	Water (an aquifer) filling the spaces between soil particles and layers of permeable rock
Risks	Waste from factories and housing areas; too much fertiliser and pesticide from farms	Fertilisers and pesticides leaching into the ground; chemicals from waste in landfills

Economic minerals

Type	Examples
Metallic minerals	Iron ore, tin, gold
Non-metallic minerals	Coal, petroleum
Rare earth minerals	Contain some of the 17 rare earth elements; used in computers, DVDs, communication devices and televisions

Rare earth elements are fairly common, but they are hard to separate because they occur together.

How coal and petroleum form

Formation of coal in three stages — Coal: dead plants are buried under sediment and mud; high pressure and heat slowly turn them into coal.

Formation of petroleum and natural gas — Petroleum and natural gas: dead marine organisms sink to the seabed and are buried; bacteria partly decompose them with little oxygen, under high temperature and pressure.

Textbook Figures 9.14 and 9.15, p. 271.

The hydrothermal process

Water underground is heated naturally by heat from the Earth (magma). This is the hydrothermal process. It produces hot springs (e.g. Sungai Klah, Perak), and the hot steam can drive a turbine to generate electricity.

Magma heats an aquifer; steam from a well drives electricity generators — Hot springs and electricity from the hydrothermal process.

Textbook Figure 9.16, p. 272.

Unplanned human activities

Deforestation, agriculture, industrialisation and open burning that are not well planned can cause erosion, flash floods, extinction of flora and fauna, pollution (water, air, thermal and sound) and global warming.

Solving the problem

Replant trees after logging; use fertilisers and pesticides in the right amounts; treat factory waste before it is released; reduce, reuse and recycle minerals so the limited supply lasts longer.

State two effects of deforestation.

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Any two: soil erosion; flash floods; less oxygen and more carbon dioxide in the air, causing global warming; loss of habitat / extinction of flora and fauna.

Summary

Remember	Key fact
Earth system	Atmosphere, hydrosphere, geosphere, biosphere
Atmosphere (bottom → top)	Troposphere (weather) → stratosphere (ozone, aircraft) → mesosphere (meteorites) → thermosphere (aurora, radio waves) → exosphere (satellites)
Ocean zones	Surface (light) → midnight (little light) → dark (no light)
Earth's layers	Crust → mantle → outer core → inner core
Rocks	Igneous (cooled magma), sedimentary (compressed layers, fossils), metamorphic (heat + pressure, hardest)
Processes	Exogenic: on the surface (weathering, erosion). Endogenic: from inside (convection, plate tectonics, volcanoes)
Geohazards	Earthquake, landslide, tsunami, volcanism; warnings from detectors and seismographs
Age of Earth	About 4.5 billion years; eras → periods; fossils show evolution and extinction
Resources	Surface and underground water; metallic, non-metallic and rare earth minerals; coal and petroleum from buried organisms; hydrothermal energy