The Lithosphere (Grade 11 NSC Matric Physical Sciences): Revision Notes

Introduction to the Lithosphere

What is the lithosphere?

When we look at Earth from space, we see a beautiful planet with continents, oceans, and swirling clouds. But what lies beneath the surface that we can see?

The lithosphere is the solid, rocky outer shell of our planet. It includes both the crust and the upper part of the mantle, forming the rigid layer that contains all the continents and ocean floors on Earth's surface.

Earth's structure

To understand the lithosphere properly, we need to know about Earth's internal structure. If we could slice Earth in half, we would see several distinct layers:

Earth consists of four main layers:

• Inner core: The solid centre made mostly of iron (about 6,378 km from surface)
• Outer core: A liquid layer also made of iron (starts at about 5,100 km from surface)
• Mantle: A thick layer of hot, flowing rock called magma that moves due to convection currents (starts at about 2,900 km from surface)
• Crust: The thin, hard outer layer that "floats" on the magma (0-100 km thick)

Why is the lithosphere important?

The lithosphere is vital to humans because it is the part of Earth that we live on and can easily access. It supports us, provides for us, and gives us a wealth of materials to use. Throughout history, humans have slowly become aware of the mineral wealth beneath their feet and have learned to use these materials for their benefit.

History of mankind and the lithosphere

Human civilisation can be understood through the materials that people used from the lithosphere. The development of technology is closely linked to our ability to extract and work with different materials from Earth's crust.

The Stone Age periods

The ancient history of humankind can be divided into several periods based on the materials they used:

Early Stone Age (2.6 million - 300,000 years ago):

• Humans used basic stone tools
• They mainly used rocks and stones found lying around
• Evidence has been found in caves at the Cradle of Humankind in South Africa

Middle Stone Age (300,000 - 50,000 years ago):

• Humans learned to use fire to treat stones before making tools
• Stone tools became more refined during this period
• Evidence found at sites like Swartkrans and Klasies River Mouth

Late Stone Age (50,000 - 10,000 years ago):

• Humans began experimenting with different materials
• They started combining stone with other natural materials
• Evidence found at Melkhoutboom Cave in the Eastern Cape

Metal Ages

Bronze Age (10,000 B.C. - 100 A.D.):

• First use of smelted copper and bronze for tools and weapons
• This represented a major technological advancement
• Evidence found in North Africa

Iron Age (100 A.D. - 1200 A.D.):

• Primitive mining for materials became common
• Furnaces were used to heat metals to make weapons and tools
• Evidence found at sites like Melville Koppies and Mapungubwe

Modern mining era

After the Iron Age ended, people began exploring new ways to access precious metals. Mining became more common as people looked for new sources of metals and minerals.

When European colonists arrived in Southern Africa, they discovered the region's rich mineral resources:

• Diamonds: Found outside Kimberley in the 1860s, leading to extensive mining operations
• Gold: Discovered near present-day Johannesburg around 1880, creating a gold rush that led to the founding of Johannesburg

These discoveries required massive labour forces and led to the development of modern industrial mining techniques.

Elements and minerals in the lithosphere

Now that we understand how humans have used materials from the lithosphere throughout history, let's examine what exactly makes up this important layer.

Composition of Earth's crust

The crust contains about 80 different elements, which occur in over 2000 different compounds and minerals. However, most of the crust's mass consists of only 8 elements:

1. Oxygen (O) - most abundant
2. Silicon (Si)
3. Aluminium (Al)
4. Iron (Fe)
5. Calcium (Ca)
6. Sodium (Na)
7. Potassium (K)
8. Magnesium (Mg)

These are called rock-forming elements because they make up the bulk of all rocks and minerals.

What are minerals?

Minerals are natural compounds formed through geological processes. The term "mineral" includes both the material's chemical composition and its structure. Minerals range in composition from pure elements to complex compounds.

A mineral can be a pure element, but more often minerals consist of many different elements combined.

Common minerals and their chemistry

Here are some important minerals and the elements they contain:

Element	Most common mineral	Chemical formula
Gold	Calaverite or pure element	Au or AuTe₂
Iron	Hematite	Fe₂O₃
Copper	Pure element or chalcocite	Cu or Cu₂S
Carbon	Diamond, graphite, coal	C
Platinum	Pure element or combined	Pt
Zinc	Sphalerite	ZnS
Manganese	Manganese dioxide	MnO₂
Chromium	Chromite	FeCr₂O₄

The rock cycle

Rocks are combinations of one or more minerals. There are three main types of rocks, and they can transform from one type to another through the rock cycle:

Igneous rocks: Form when magma cools and solidifies (e.g., granite, basalt)

Sedimentary rocks: Form when rock fragments, organic matter, or sediments are deposited and compressed over time (e.g., sandstone, limestone)

Metamorphic rocks: Form when existing rocks are subjected to intense heat and pressure (e.g., slate, marble)

Ores and mining

Many elements of interest to humans (like gold, iron, and copper) are unevenly distributed in the lithosphere. In places where these elements are abundant, it becomes profitable to extract them through mining.

Ore is a volume of rock that contains minerals which make it valuable for mining. If the concentration of valuable minerals is too low, the cost of extraction becomes more than the money that would be made from selling them.

Mineral distribution in South Africa

South Africa is particularly rich in mineral resources. The country contains significant deposits of gold, platinum, diamonds, chrome, copper, iron, manganese, and many other valuable minerals.

As humans, we are particularly interested in:

• Metal-containing ores (for tools, construction, electronics)
• Energy-producing minerals (coal, uranium for power generation)
• Gemstones (diamonds, precious stones for jewellery)