UNIT 18 SURFACE OF THE EARTH

What features are found on the Earth’s surface? 1. Continents and Islands Continents – 7 large masses of land - made up of Africa, Antartica, Asia, Australia, Europe, North America and South America - largest continent is Asia Islands – thousands of small land masses surrounded by water

The seven continents

2. Oceans, seas, lakes and rivers 70% of the Earth’s surface is covered by water surrounding the continents and islands Pacific ocean is the largest and deepest ocean

3. Mountains and hills Some mountain ranges are found on the ocean floor. Highest point on Earth is Mt. Everest (8848 m above sea level) in the Himalayas mountain ranges Lowest point on Earth is the Mariana Trench in the Pacific Ocean (about m below sea level) Mount Everest Marianas trench

4. Other features Plains Volcanoes Valleys Desert – make up 1/3 of the Earth’s land surface Classified into: Hot desert – high temperature all year long Temperate desert – hot summers and freezing cold winters

What can change the Earth’s surface? 1. Rain washes away and exposes soil resulting in barren land acid rain (formed when sulphur dioxide and oxides of nitrogen dissolve in rainwater) removes nutrients from soil, kill aquatic organisms, corrodes and damages buildings

2. Running water sediments hit against rocks on rivers and grind against the riverbed and riverbanks rocks loosen and break into pieces by physical grinding (abrasion) flow of water carries loosened materials away forming caves and valleys overtime

3. Wind can pick up small particles of sand, soil and rocks abrasion by wind particles change shape of rocks

4. Sunlight Thermal expansion – expansion of rocks in the day and contraction at night - common in areas with large temperature change such as the desert Frost action – water trapped in rocks may freeze to become ice and expand causing cracks to enlarge Thermal expansionFrost action

5. Tidal waves waves crash onto shores and against cliffs sediments hit and scrape against land surfaces loosening and smoothening materials outgoing waves carry loosened materials away

What processes change the Earth’s surface? 1. Slow processes occur over time Include: WEATHERING – physical and chemical break down of rocks and other land structures Agents are: rain, water, sunlight, tidal waves, wind EROSION – washing away of soil and rocks Agents are: running water, tidal waves, rain, wind

Weathering of rocks Erosion of soil

2. Rapid process require a very short time for changes to be observable Include: LANDSLIDES - movement of rocks down a slope

VOLCANIC ERUPTIONS AND EARTHQUAKES slow plate movements can cause volcanic formation and earthquakes

How do human activities change the Earth’s surface? 1. Industrialization Factories, power plants and houses Dams Logging Mining Roads and bridges

dam logging mining bridge

2. Farming greater demand for food more land required for better yielding crops

3. Land reclamation rocks and other Earth materials are excavated from hills to reclaim land from the sea needed to build housing for expanding population

How can we prevent the destruction of the Earth? 1. Preventing erosion Do not cut trees unnecessarily Grow trees and plants on exposed soil Keep soil damp during hot weather to lessen erosion by wind

2. Preventing landslides regrow trees and plants on barren slopes do not cut down trees unnecessarily place a wire mesh over rocks and exposed soil

3. Preventing abrasion place breakwaters, rocks and concrete along rivers and river banks

4. Preventing floods build a strong, thick wall (dyke) along the river

Sources: BBC world challenge links