Structure of Earth and Types of Rocks
Complete Notes & Free Quiz

Geography is the study of our planet Earth, its land, and the people living on it. The word comes from Greek: geo (the Earth) + graphein (to write) → "to write about the Earth".

Three main branches:
1. Physical Geography — study of the Earth's natural features (land, mountains, rivers, climate, soil)
2. Human Geography — study of people and their activities (population, settlement, economic activity)
3. Environmental Geography — study of how people interact with nature (mining, pollution, climate change)

Weather is the condition of the atmosphere at any given time (changes daily).
Climate is the average weather conditions recorded at a particular place over many years — usually more than 30 years.

The Earth has three distinct layers:

1. Crust — outermost layer; 5–60 km thick; rigid and broken into plates; thin under oceans (~5 km), thick under continents (~40 km)

2. Mantle — below the crust; ~2,000 km thick; semi-solid rocks; temperature ~1,000°C; contains convection currents that move the plates

3. Core — innermost part; divided into:
• Outer Core: ~2,250 km thick; liquid nickel and iron (Ni-Fe alloy); ~4,400°C
• Inner Core: ~1,250 km thick; solid iron; >5,430°C (solid despite extreme heat because of enormous pressure)

Convection currents are circular heat movements in the mantle. When the part near the core heats up, the current rises toward the crust, cools down, flows along the bottom of the crust, then sinks back down to be reheated. This repeated circular motion is what drives the movement of Earth's tectonic plates.

Pangaea was a supercontinent — millions of years ago, all land on Earth was one huge landmass called Pangaea. Over time, it gradually split apart into the continents we see today.

The Continental Drift Theory was proposed by Alfred Wegener in 1912. He argued that all continents were once joined together and have been slowly drifting apart over millions of years. Evidence includes: matching coastlines, similar fossils on separate continents, and identical rock formations on different continents.

1. Convergent Boundary — plates move TOWARD each other → mountains form, earthquakes and volcanoes occur (e.g. Himalayas formed by India-Eurasia collision)

2. Divergent Boundary — plates move APART → mid-ocean ridges and rift valleys form

3. Transform Boundary — plates slide PAST each other → earthquakes occur (e.g. San Andreas Fault)

Pakistan sits at the meeting point of three major tectonic plates: the Eurasian Plate, the Indian Plate, and the Arabian Plate. This makes Pakistan highly vulnerable to seismic (earthquake) activity.

Major fault lines in Pakistan include the Chaman Fault and the Makran Subduction Zone. The 2005 Kashmir earthquake was caused by the collision of the Indian Plate with the Eurasian Plate.

1. Igneous Rocks — formed when molten magma cools and solidifies. Examples: granite, basalt, obsidian

2. Sedimentary Rocks — formed by layers of sediment (sand, mud, shells) being compressed over time. Examples: sandstone, limestone, shale. Often contain fossils.

3. Metamorphic Rocks — formed when existing rocks are changed by extreme heat and pressure deep inside the Earth. Examples: marble (from limestone), slate (from shale)

The Rock Cycle is the continuous process by which rocks transform from one type to another over millions of years:

Magma cools → Igneous rock → weathered and eroded → sediments deposited → compressed → Sedimentary rock → subjected to heat and pressure → Metamorphic rock → melted into magma again → cycle continues

GIS (Geographic Information System) — a computer-based system that collects, stores, analyzes, and displays geographical data as maps and layers.

GPS (Global Positioning System) — a satellite-based system that gives the exact location of any point on Earth using latitude and longitude.

Google Maps — a digital mapping tool that uses satellite imagery and GPS data to help people navigate and explore geographic information.

These technologies are used for: urban planning, disaster management, land surveys, navigation, and tracking environmental change.