TNPSC Environmental Scientist - Lithosphere - Material
Lithosphere – Study Notes
Unit I: Introduction to Environment (30 Questions) Environment: Components
– Segments – Atmosphere: Troposphere – Stratosphere – Mesosphere – Thermosphere
– Lithosphere: Crust – Mantle – Core – Hydrosphere: Fresh water and saline water -
Introduction
The lithosphere is the rigid,
outermost layer of the Earth. It includes the crust and the uppermost mantle
and forms the continents and ocean floors. It is where human civilization
exists, agriculture is practiced, and natural resources like minerals and
fossil fuels are found.
Understanding the lithosphere is
essential in studying geology, natural hazards, soil science, landforms, and
human-environment interactions.
1.
What is the Lithosphere?
- Derived from the Greek words "lithos"
(stone) and "sphaira" (sphere).
- It is the solid outer part
of the Earth.
- Ranges from about 5 km under
oceans to about 70 km under continents.
- Divided into tectonic plates
which move slowly over the asthenosphere.
Components:
- Continental crust (granite-rich): Thick and less
dense.
- Oceanic crust (basalt-rich): Thin and more
dense.
- Upper mantle: Solid portion beneath the
crust that contributes to plate movements.
2.
Structure of the Earth
The Earth is composed of three major
layers:
|
Layer |
Composition |
Depth
Range |
|
Crust |
Rocks, soil, minerals |
0–70 km |
|
Mantle |
Silicate rocks (magnesium, iron) |
70–2900 km |
|
Core |
Iron and nickel (liquid & solid) |
2900–6371 km |
The lithosphere includes the crust
and the rigid upper mantle.
1. Crust – The Earth's Outer
Shell
📌 Overview:
- The crust
is the thin, outermost layer of the Earth where we live.
- It's
like the "skin" of the Earth, floating on top of the mantle.
Types:
- Continental
Crust: Thicker (30–70 km), less dense, mostly
granite.
- Oceanic
Crust: Thinner (5–10 km), more dense, mostly
basalt.
Composition:
- Made
of solid rocks and minerals.
- Elements:
Oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium.
🌡 Temperature:
- Ranges
from 0°C to 700°C, depending on depth.
2. Mantle – The Earth's
Middle Layer
📌 Overview:
- Lies
beneath the crust and extends to about 2,900 km below the surface.
- Makes
up about 84% of Earth's volume.
Structure:
- Upper
Mantle (includes asthenosphere, partially molten and
plastic-like).
- Lower
Mantle (more rigid due to pressure).
Composition:
- Rich
in silicate minerals containing magnesium and iron.
- Rocks
are in a semi-solid, flowing state.
🌡 Temperature:
- Between
700°C to 4,000°C.
🔁 Convection Currents:
- Hot
mantle rocks rise and cooler ones sink.
- These
currents drive plate tectonics, moving Earth's crust.
3. Core – The Earth's Inner
Engine
📌 Overview:
- The core
is the central part of Earth, divided into two layers:
- Outer
Core (liquid)
- Inner
Core (solid)
Outer Core:
- Depth:
2,900–5,100 km
- State:
Liquid
- Composition:
Mostly liquid iron and nickel
- Temperature: 4,000–6,000°C
- Function:
Movements of this layer generate Earth’s magnetic field
Inner Core:
- Depth:
5,100–6,371 km
- State:
Solid (due to immense pressure)
- Composition:
Iron and nickel
- Temperature:
Similar to the Sun's surface (~5,700°C)
3.
Types of Lithosphere
a)
Continental Lithosphere
- Thicker (30–70 km), older, and
less dense.
- Composed mainly of granite.
- Forms continents and large
landmasses.
b)
Oceanic Lithosphere
- Thinner (5–10 km), younger, and
denser.
- Composed mainly of basalt.
- Forms ocean floors and
mid-ocean ridges.
4.
Composition of the Lithosphere
a)
Minerals:
- Naturally occurring, inorganic
solids with a definite chemical composition.
- Examples: Quartz, feldspar,
mica, calcite, olivine.
b)
Rocks:
- Solid aggregates of one or more
minerals.
- Types of rocks:
- Igneous (formed from magma): e.g.,
granite, basalt.
- Sedimentary (formed from deposition):
e.g., limestone, sandstone.
- Metamorphic (transformed by
heat/pressure): e.g., marble, slate.
5. Landforms of the Lithosphere
Landforms are the natural physical
features of the Earth’s surface, shaped by geological and geomorphological
processes.
a)
Mountains
- Elevated landforms formed by
tectonic forces or volcanic activity.
- Examples: Himalayas, Andes.
b)
Plateaus
- Flat elevated areas.
- Example: Deccan Plateau
(India), Colorado Plateau (USA).
c)
Plains
- Flat and low-lying areas formed
by river deposits.
- Fertile and densely populated
regions.
d)
Valleys, Basins, Volcanoes
- Valleys: Depressions formed by
rivers or glaciers.
- Basins: Low areas often filled
with sediments.
- Volcanoes: Openings through
which lava, ash, and gases erupt.
6.
Plate Tectonics and the Lithosphere
The lithosphere is divided into
tectonic plates that float over the asthenosphere.
a)
Major Plates:
- Eurasian, African,
Indo-Australian, Pacific, North American, South American, Antarctic.
b)
Plate Boundaries:
- Divergent: Plates move apart (e.g.,
Mid-Atlantic Ridge).
- Convergent: Plates move toward each other
(e.g., Himalayas).
- Transform: Plates slide past each other
(e.g., San Andreas Fault).
c)
Effects of Plate Movements:
- Earthquakes
- Volcanic eruptions
- Mountain formation
- Ocean trench development
7.
Natural Resources of the Lithosphere
The lithosphere contains a wealth of
natural resources crucial to human development.
a)
Minerals:
- Metallic: Iron, copper,
bauxite, gold.
- Non-metallic: Mica, limestone,
gypsum.
b)
Fossil Fuels:
- Coal, petroleum, natural gas –
sources of energy formed from ancient organisms.
c)
Soil:
- Top layer of the lithosphere
vital for agriculture.
- Formed by weathering of rocks
and organic matter.
8. Soils and Soil Formation
a)
Definition:
Soil is the uppermost layer of the
Earth’s crust that supports plant life.
b)
Soil Profile:
- O Horizon: Organic matter.
- A Horizon: Topsoil, rich in nutrients.
- B Horizon: Subsoil, less organic matter.
- C Horizon: Weathered parent rock.
c)
Soil Formation Factors:
- Parent rock
- Climate
- Organisms
- Time
- Relief (topography)
d)
Types of Soil:
- Alluvial: Fertile, found in river
valleys.
- Black Soil: Ideal for cotton, found in
volcanic regions.
- Red Soil: Rich in iron, found in dry
areas.
- Laterite Soil: Leached soils in high
rainfall areas.
9. Processes Affecting the Lithosphere
a)
Internal Processes (Endogenic):
- Caused by forces inside the
Earth.
- Examples: Volcanism,
earthquakes, mountain building.
b)
External Processes (Exogenic):
- Caused by weathering, erosion,
transportation, and deposition.
- Shaped by agents like rivers,
glaciers, wind, and sea waves.
10.
Environmental Issues Related to the Lithosphere
Human activities are degrading the
lithosphere, leading to long-term impacts.
a)
Soil Erosion:
- Removal of topsoil due to wind,
water, or human activity.
- Leads to desertification and reduced
agricultural productivity.
b)
Deforestation:
- Clearing of forests for
urbanization and agriculture.
- Causes loss of biodiversity,
increases erosion.
c)
Mining:
- Extraction of minerals disrupts
land and pollutes water and air.
d)
Urbanization and Land Use Change:
- Concrete surfaces reduce
groundwater recharge.
- Agricultural land converted to
buildings leads to food insecurity.
11. Conservation of the Lithosphere
a)
Sustainable Agriculture:
- Use of organic farming, crop
rotation, and contour plowing to prevent soil degradation.
b)
Afforestation and Reforestation:
- Planting trees to prevent
erosion and maintain ecological balance.
c)
Regulated Mining Practices:
- Reduce environmental impact by
using eco-friendly technologies and reclamation methods.
d)
Soil Conservation Techniques:
- Terracing, strip cropping,
mulching, check dams.
12. Importance of the Lithosphere
- Supports Life: Provides habitat and food
sources.
- Agricultural Base: Soil allows the cultivation
of crops.
- Natural Resource Reservoir: Supplies minerals, water, and
fossil fuels.
- Foundation for Infrastructure: Buildings, roads, and cities
are all based on land.
- Environmental Regulator: Participates in carbon and
nutrient cycles.
