Earth: Home Sweet Home
4.6 Billion BC
-1004600 -1004600

NAT

THIRD PLANET, SOLAR SYSTEM
	You may have heard that Earth is a mere speck near the edge of our galaxy, and that is true.  But don't underestimate Earth, it is actually an amazing -- but delicate -- little planet.
	As many environmental\ists have pointed out, Earth's atmosphere has just the right amount of ozone and carbon dioxide.  If there was much more or less of either, Earth's surface would be too hot or cold.
	Or, suppose Earth was a bit closer to the sun.  The added heat would prevent the clouds from raining.  But move it a little further away and too little water would evaporate from the oceans, so clouds would not form.
	If you painted the Earth's surface a darker color, it would absorb too much heat.  But paint it a lighter color and the surface would reflect too much heat and become too cold.
	While Earth is small, it's distance from the sun and tilt and rotation and gravity and many other factors make it ideal for life.
	This wonderful planet is a slightly flattened ball measuring about 24,860 miles around at the equator.  It is covered with a 5- to 40-mile thick crust divided into plates that slide slowly around on the mantle, a mass of hot, gooey rock surrounding a core of molten metal.
	Because Earth is slightly tilted in relation to the sun, either its north or south end is closer to the sun at any time.  Sunlight strikes the closer end more directly and intensely, causing summer, and strikes the further end at a greater angle and less intensely, causing winter.
	Today, many scientists are encouraging us to change our lifestyles so we don't upset the delicate balance that makes Earth a wonderful place to live. They are concerned that some human activities, such as burning fossil fuels, clearing forests and releasing man-made chemicals into the atmosphere, may upset the planet's environment.