Author: ahaelzle
Company: Wellington Catholic District School Board

LIFE ON PLANET EARTH
The Spheres of Earth
1.	The Atmosphere – The layer of gases surrounding the Earth.  It is made up of about 78% Nitrogen, 21% Oxygen, and the remaining <1% includes argon, water vapour, carbon dioxide, and a variety of other gases.  The atmosphere acts like a blanket and moderates surface temperatures.  This insulation prevents excessive heating during the day and cooling during the night.  The atmosphere also blocks some incoming solar radiation, including most ultraviolet light. Without the atmosphere most of Earth’s species would not be able to survive.

2.	The Lithosphere – Earth’s solid (rocky) outer layer.  It consists of the rocks and minerals that make up the mountains, the ocean floor, and the rest of Earth’s solid landscape.

3.	The Hydrosphere – All of Earth’s water in solid, liquid, and gas form.  The hydrosphere consists of all the water on, above, and below the Earth’s surface.  It includes oceans, lakes, ice, groundwater, and clouds.  Nearly all the water on Earth (97%) is contained in the oceans.

The Biosphere
The zone around Earth where life can exist.  Where life can exist within the lithosphere, atmosphere, and hydrosphere. (See page 30 for a diagram)
All living things need space, water, and nutrients to survive.  The supply of these resources is limited.  The availability of these resources places a limit on the number of individuals of a species that can survive.  

What is the Gaia hypothesis? (read the bottom of pg 30)