Chapter 2The Physical World

Section 1Planet Earth

Our Solar System

• The sun and the objects that revolve around it including the Earth• Sun’s mass creates gravity which keeps the objects revolving around it

Planets

• Spherical objects orbiting the sun• Inner planets: Mercury,

Venus, Earth & Mars• Outer planets: Jupiter,

Saturn, Uranus & Neptune

Dwarf planets

• Small round bodies that orbit the sun but have not cleared the area around their orbits of other orbiting bodies• Ex: Pluto & Ceres

2 types

1. Terrestrial planets – have solid, rocky crusts; Mercury, Venus, Earth & Mars

2. Gas giant planets – more gaseous & less dense; larger in diameter; Jupiter, Saturn, Uranus, & Neptune

Asteroids

• Small, irregularly shaped, planet-like objects found mainly between Mars and Jupiter in the asteroid belt

Comets

• Icy dust particles & frozen gases• Orbits are inclined to Earth’s orbit from any direction

Meteoroids

• Pieces of space debris (rock & iron)• Usually burn up when reach the Earth’s surface

Earth

• Rounded object wider around the center than from top to bottom• Diameter = 7,930 miles at

the Equator• Circumference = 24,900

miles

Earth’s surface

• 70% water – hydrosphere: oceans, lakes, rivers & other bodies of water• 30% land – lithosphere: islands, continents & ocean basins

Other spheres

• Atmosphere – layer of gases extending above the Earth’s surface; air we breathe; 78% nitrogen, 21% oxygen• Biosphere – part of Earth that supports life

Section 2Forces of Change

Layers of Earth

1. Core – super-hot, solid inner layer of the planet surrounded by a band of melted iron & nickel (liquid outer core)

2. Mantle – thick layer of hot, dense rock consisting of silicon, aluminum, iron, magnesium, oxygen & other elements; continually rises, cools, sinks, warms up & rises again releasing 80% of generated heat

3. Crust – outer layer of the Earth’s surface; thin layer of rock (2-75 miles thick); broken into great slabs known as plates which float on a partially melted layer in the upper portion of the mantle & carry the oceans and continents

Pangaea

• Supercontinent of Earth’s landmasses that broke apart into the smaller continents in existence today

Continental drift

• Theory that continents were once joined and slowly drifted apart

Plate tectonics

• The physical processes that create the earth’s physical features• May have created oceans & mountain ranges as well as the continents

Mountains

• Created where giant continental plates collide (Himalaya Mtns) or when a sea plate collides with a continental plate through a process known as subduction (Andes Mtns)

Subduction

• Process in which a heavier sea plate dives beneath the lighter continental plate and becomes molten material which then bursts through the crust to form volcanic mountains

Accretion

• Pieces of the Earth’s crust come together slowly as the sea plate slides under the continental plate leveling off seamounts (underwater mountains) and piling up debris in trenches• Causes continents to expand

Folds

• Bends in the layers of rock created as moving plates squeeze the Earth’s surface and it buckles

Faults

• Cracks created in the Earth’s surface as plates grind or slide past each other• San Andreas Fault in California

Earthquakes

• Sudden, violent movements of tectonic plates along a fault line• May change the surface of the land and the floor of the ocean

Ring of Fire

• Zone of earthquake and volcanic activity around the perimeter of the Pacific Ocean

Volcanoes

• Mountains formed by lava or by magma that breaks through the Earth’s crust often rising along plate boundaries where one plate plunges beneath another

Weathering

• Chemical or physical processes, such as freezing, that break down rocks

Physical weathering

• Occurs when large masses of rock are physically broken down into smaller pieces • Ex: water seeps into the

cracks of a rock, freezes, expands and causes the rock to split

Chemical weathering

• Changes the chemical makeup of rocks • Ex: rainwater containing carbon dioxide dissolving rocks such as limestone

Wind erosion

• Involves the movement of dust, sand, and soil from one place to another

Glacial erosion

• Large bodies of ice moving across the Earth’s surface picking up rocks and soil, changing the landscape

Moraines

• Large piles of rock and debris left behind as glaciers melt and recede

2 types of glaciers

1. Sheet glaciers – flat, broad sheets of ice which advance a few feet each winter and recede in the summer (cover most of Greenland & Antarctica)

2. Mountain glaciers – located in high mountain valleys with a cold climate

Water erosion

• Occurs when springwater and rainwater flow downhill, cutting the land and wearing away the soil and rock forming first gullies and then canyons

Soil

• Product of weathering and biological activity• 5 factors: 1. Climate (wind, temperature,

& rainfall) 2. Topography (shape & position

of Earth’s physical features)

3. Geology (determining the original rock material influences depth, texture, drainage, & nutrient content)

4. Biology (living & dead plants and animals add organic matter)

5. Time (of other factors)

Section 3Earth’s Water

Water cycle

• Regular movement of water on the Earth• Evaporation – changing of liquid water into vapor (gas) caused by the sun’s energy

• Condensation – process of excess water vapor changing into liquid water when warm air cools• Precipitation – rain, snow or

sleet which falls to the Earth when clouds gather more water than they can hold; sinks into the ground, collects in streams & lakes to return to the oceans

Oceans

• 5 divisions of the water circling the Earth• Pacific, Atlantic, Indian, Arctic and Southern (extends from the coast of Antarctica north to 60º S latitude)

Desalination

• Process of turning saltwater into freshwater

Freshwater

• 3% of the Earth’s total water supply• Very little is actually available for human consumption

Groundwater

• Freshwater that lies beneath the Earth’s surface and comes from rain and melted snow• Source for wells and springs

Aquifer

• Underground porous rock layer saturated by very slow flows of water