Earth Movements and Major Landforms
- Earth's Face is Always Changing:
The Earth's surface is constantly being reshaped.
- Two Main Forces Shaping Land:
- Denudation Agents (Wearing Down):
These are forces that wear away the land:
- Running water (rivers)
- Rain
- Frost (ice)
- Sun
- Wind
- Glaciers (large ice rivers)
- Waves (ocean)
- Think of them as sculptors
slowly carving away at the Earth.
- Earth's Crust Movements (Building Up):
Movements inside the Earth that create mountains, plateaus,
and plains.
- These movements make the basic shape
of the land.
- Denudation agents then modify
these shapes.
- Orogenic Movements = Mountain Building:
- "Orogenic" means related to
mountain formation.
- Earth has had many mountain-building
periods throughout history.
- Text mentions nine orogenic
movements in geological time!
- These movements fold and fracture
the Earth's crust, creating mountains.
- Examples of Orogenic Movements and
Mountains:
- Pre-Cambrian Orogenies (Very Old):
- Happened 600-3,500 million years ago
(super ancient!).
- Caledonian Orogeny (Old):
- About 320 million years ago.
- Raised mountains of Scandinavia
and Scotland.
- Also found in North America.
- Ancient mountains:
Worn down over time, not as dramatic looking now.
- Hercynian Orogeny (Middle-Aged):
- About 240 million years ago.
- Formed ranges like:
- Ural Mountains
(Russia)
- Pennines & Welsh Highlands
(Britain)
- Harz Mountains
(Germany)
- Appalachians
(America)
- High Plateaus of Siberia &
China.
- Reduced in size:
Also worn down by erosion over time.
- Alpine Orogeny (Youngest):
- About 30 million years ago.
- We are living close to this
period!
- Young Fold Mountains:
Created huge "buckled up" and "overthrust"
mountains.
- Examples (Loftiest & Most
Imposing):
- Alps
(Europe)
- Himalayas
(Asia)
- Andes
(South America)
- Rockies
(North America) (See Figure 17 in your text).
- Very High Peaks:
Some peaks are several miles high.
- But... even these will be worn
down eventually!
- Mountain Cycle:
- Mountains are raised up
by Earth movements.
- Mountains are worn down
by erosion.
- Eroded materials
become sediment.
- Sediment forms new rocks.
- New rocks can be uplifted
to form new mountains in the future.
- It's a continuous cycle of mountain
building and wearing down over millions of years.
In Simple Words:
Earth's surface is shaped by two main things: forces that wear it down (like
rain and wind) and forces from inside the Earth that build it up (Earth
movements). Mountain ranges are created by huge Earth movements called
orogenies. There have been many orogenies in Earth's history, from very ancient
ones to the more recent Alpine orogeny that formed the tallest mountains like
the Himalayas and Alps. Even these giants will eventually be eroded away, and
the cycle will continue!