Physical Connections Chapter 3

All life is possible on Earth because of 4 conditions: Constant, relatively mild temperature Constant, relatively mild temperature –-50° to 50° C (a span of about 100°) Abundance of water Abundance of water Sufficient quantities of gas to sustain life Sufficient quantities of gas to sustain life –Oxygen –Carbon dioxide (CO 2 ) –Nitrogen Atmosphere thick enough to protect living things from the sun’s ultraviolet radiation Atmosphere thick enough to protect living things from the sun’s ultraviolet radiation

These 4 conditions, in turn, depend on … Earth’s distance from the sun Earth’s distance from the sun –So only a small proportion of the sun’s energy reaches life Earth’s rotation on its axis and its revolution around the sun Earth’s rotation on its axis and its revolution around the sun –So solar heat is evenly distributed around the planet Earth’s gravitational field Earth’s gravitational field –So the atmosphere is held in place Earth’s magnetic field Earth’s magnetic field –Protects Earth from cosmic radiation and particles

Earth’s stable temperature range is maintained by… The Greenhouse effect The Greenhouse effect Sunlight passes through the atmosphere and warms the surface of Earth Sunlight passes through the atmosphere and warms the surface of Earth –Some heat is radiated back as long-wave infrared radiation –In the atmosphere it is absorbed by molecules of CO 2 and H 2 O, and then reflected back to the surface as heat

Earth’s stable temperature range is also maintained by… Plant cover Plant cover –Plant photosynthesis and respiration control levels of water vapour and carbon dioxide (we breathe in oxygen and release CO 2; plants breathe in CO 2 and release oxygen) Albedo (the ability of a surface to reflect solar energy) Albedo (the ability of a surface to reflect solar energy) –Sunlight is reflected from white or light surface (sand) and absorbed by dark surface (vegetation, asphalt)

The importance of water Water cycle (Page 52) Water cycle (Page 52) Absorbs heat, so oceans distribute heat around the world Absorbs heat, so oceans distribute heat around the world Oceans act as reservoirs for evaporation into the atmosphere Oceans act as reservoirs for evaporation into the atmosphere Acts as a solvent to distribute nutrients through the soil for plants and other organisms Acts as a solvent to distribute nutrients through the soil for plants and other organisms Provides hydrogen necessary for photosynthesis Provides hydrogen necessary for photosynthesis

And finally, water Makes up all living things Makes up all living things –All organisms are more than 50% water –Humans are 70% water Is the medium by which minerals vitamins, and foods are carried through the body Is the medium by which minerals vitamins, and foods are carried through the body Is the solution in which metabolic (energy producing) reactions take place and by which waste is removed from the body Is the solution in which metabolic (energy producing) reactions take place and by which waste is removed from the body

The importance of gases Earth’s atmosphere is made up of Earth’s atmosphere is made up of –78% nitrogen –21% oxygen –0.03% CO 2 –Small amounts of other gases All foods are made up of carbohydrates, fats, and proteins All foods are made up of carbohydrates, fats, and proteins –These are made up of nitrogen, oxygen, hydrogen, and CO 2

The importance of the atmosphere Earth covered by a layer of gases km thick Earth covered by a layer of gases km thick Helps maintain Earth’s temperature Helps maintain Earth’s temperature Shields Earth from cosmic particles (of all sizes) Shields Earth from cosmic particles (of all sizes) Oxygen makes up 21% of atmosphere Oxygen makes up 21% of atmosphere –In stratosphere it exists as ozone, which filters out excessive ultraviolet radiation (which can be extremely dangerous)