Planet Earth is home to 6,000,000,000 people and over 13,000,000 species of plants and animals. The Earth is the most unique object in the universe and often referred to as the Goldilocks Planet. The porridge is just right for life to exist. Air and water, absolutely essential, for without these two ingredients all life will perish. Science refers to Earth as living in the right habitable zone. Just the correct distance from the Sun and our star is just the correct temperature for Earth. We are saturated with life on this planet due to atmosphere, water and temperature.
Earth's atmosphere has five layers. Astronauts viewing Earth from space refer to the atmosphere to be as thin as an onionskin. We humans live in the Troposphere and this is where 99% of our weather occurs. Above this layer is the Stratosphere and ozone layers, then the Mesosphere, the Thermosphere and finally the Exosphere. Our layers of atmosphere are very complex and they all play an important role in our survival. The ozone layer absorbs most of the ultraviolet radiation coming from the Sun and offers us protection from this harmful radiation. The Mesosphere is the zone in which most meteors burn up for us to observe as "shooting stars". Current estimates are about 40,000 metric tons collide with Earth annually and burn up. Gravity will pull this meteoric dust back to Earth and humans and animals breath in this dust. It does not contain harmful radiation of any type and is microscopic. In the Thermosphere temperatures can rise to 1,727 degrees Celsius. This area of space is where the shuttle orbits Earth. The Exosphere extends approximately to 600 miles above the surface and here what is left of our atmosphere merges with interplanetary gases, or space. In this region only hydrogen and helium are the prime components and are present at extremely low densities. It is important to note that our atmospheric layers shields us from dangerous cosmic radiation, which are highly energetic pieces of matter excited to nearly the speed of light. They pass through everything in their path and cause tremendous damage to the molecular structure of whatever they pass through and that is why they are a hazard to humans. Most arrive as secondary particles here on Earth. Occasionally, primary particles do impact the surface. The observatory has a saturated cloud chamber charge with dry ice and 200 proof alcohol that allows visitors to observe where they have passed.
Our Earth has great weight or mass, in fact 5,972,000,000,000,000,000,000 tons, (5.972 sextillion tons). Earth does not compare to the Sun, as its mass is two octillion tons, (2,000,000,000,000,000,000,000,000,000 tons). Yes, these numbers are legitimate. Never think small when you consider the universe.
In the center of the Earth is the core, a solid body of iron and nickel almost 2,100 miles in diameter. Above the core is the outer core extending approximately 1,400 miles thick and is molten. The estimated temperature is 9,000 degrees Fahrenheit. As the Earth spins on its axis this interaction between the solid core and molten outer core creates electricity and magnetism. The magnetic poles, both north and south are always shifting slowly. Mariners and aviators must refer to charts that show l a compass rose with the increase or decrease of magnetic variation. Most charts will exhibit lines of magnetic variation and these lines must be used along with the vessels deviation to correct the magnetic heading or convert to true north or south. Gyrocompasses are independent of the Earth's magnetic field. Thank Foucault for this. Their only error is caused by friction and vibration of their internal machinery. Beyond the outer core is the mantle and finally the crust. This is where volcanism occurs continually. The face of the Earth is constantly changing and this is caused by weather, tectonics and to a lesser degree meteorite impacts and human intervention. Earth is alive, a very dynamic planet and is always changing its face of appearance, most of the time slowly. However, catastrophic events such as the recent tsunami in the Far East and Mount St. Helens reveal that sometimes the Earth changes its appearance very quickly and does so with devastation.
Take the time to study a chart or a globe of our planet. You will note that a good portion of Earth's land mass is in the northern hemisphere (the land hemisphere) and (the water hemisphere) south of the equator. Oceans, lakes, rivers, streams and glaciers cover 70% of the surface of Earth. Only 3%of the water on this planet is freshwater and of that amount only .03% is usable by humans. Most of our drinking water comes from freshwater rivers. The remaining 30% is our land mass and this where humans live. Taking the atmosphere and water into account and understaning the warning that science offers us about global warming and pollution we must become better stewards of these precious gifts to ensure that future generations may enjoy life on this most unique planet in the universe.