Outline of Earth Science by Ellin Beltz
You are here
Part I
Atoms, Minerals, Rocks, Geological Time
Part II
Plate Tectonics, Earthquakes, Volcanos, Geological Structures
Part III
Fresh Water and its Landforms
Part IV
Part V
2005 by Ellin Beltz

Outline of Earth Science


The Universe has existed for about 15 billion years.

  • In it, the speed of light is always faster than speed of sound.
  • Therefore the first event generated a large flash of light outwards in all directions long before it would have made a big, or any sort of bang.
  • Stars are suns. Billions and billions of suns (thank you, Carl Sagan).
  • Galaxies are collections of suns. Our sun is in a galaxy which we see edge on as the Milky Way.
  • The sun's average temperature is about 5480 degrees Celsius, or 548 times boiling water.

Our sun has a Solar System which includes Mercury, Venus, Earth, Mars, the asteroid belt, Jupiter, Saturn, Neptune, Uranus, Pluto/Charon and the Oort Cloud of comets. There is a regular spacing to the planets. Using the Sun-Mercury distance as one unit, the spacing is 1:1:2:3:5:8 and so on, more or less and excluding Pluto/Charon. The age of the Earth and Moon are about the same; about 3.9 billion years.

Earth is about 25,000 miles around. This was first calculated by Eratosthenes, a teacher at the Alexandria Museum about 239 BC. He assumed that the sun's rays were parallel and that the sun was a great distance away. An ancient well is said to have reflected the light directly upward to light a monument and was quite a tourist attraction for several thousand years. So everyone knew that the sun stood overhead in Aswan on Summer Solstice. Eratosthenes measured the angle of the sun at noon in Alexandria and found it was about 7.5 degrees out of a total of 360. Since 7.5 divided by 360 degrees in a circle works out to about 1/50 of a circle, he now knew the angle of the Sun's rays between Alexandria and Aswan. The Egyptian post office is said to have provided the ground distance between the two points as the equivalent of 500 miles. So if 500 miles is 1/50th of a circle, the whole circle is 25,000 miles around. Almost spot on, as it turns out. From this, he calculated that it is about 8,000 miles to the center of the Earth.

But his accomplishment is dwarfed by Mesopotamian astronomers who described the following systems almost exactly, but in ancient Sumerican terms as early as 2,500 BC and copied and recopied as "religious texts" for centuries afterward along with the construction mathematics to build observatories and instruments.

It has been known since ancient times that:

  • The North Pole appears to point to a north star. Right now it's a star called Polaris. Stars rotate around Polaris; some are always visible at night, others appear to rise and set. Stars which rotate closest to Polaris cannot be seen from the Southern Hemisphere.

  • In the Southern Hemisphere, the Southern Cross points toward the pole, but there is no star exactly there right now. Starts rotate around the southern pole; some are always visible at night, others appear to rise and set. Starts which rotate closest to the southern pole cannot be seen from the Northern Hemisphere.

  • The stars which rise and set can be seen from both hemispheres.

  • The plane in which most of the planets in our Solar System rotates is called the plane of the ecliptic. The zodiac constellations mark the plane of the ecliptic and the planets, the moon and the sun all appear to rise and set in this plane.

  • The moon revolves around the Earth once ~ every 28 days and rotates on its axis once in the same time; keeping its face always towards the Earth.
DayPhaseColorRising time
1Fullwhiteat or just after sunset
7Last Quarterhalf black/half whitenear midnight
14New Moonblacknear sunrise
21First Quarterhalf white/half blacknear noon

  • The Earth's axis tilts about 23.5 degrees now. It wobbles over about 26,000 years in a full circle so that while Polaris is the North Star at the present time, the north polar star changes slowly over time and will return to being Polaris again in about another 26,000 years.

  • We know that our axis points at Polaris - on a human life span and that the Sun is in the middle of the Solar System.

  • We know that there is a solid core in the middle of the Earth which rotates within a liquid outer core very rapidly and generates the Earth's magnetic field. The axis of the solid core is not the same as the axis of the Earth; it moves, but returns to about the same point on Earth's surface once every 400 years. This is why the magnetic pole and the axial pole are not the same.

  • The Earth's orbit is an ellipse, not a circle. It is closest to the sun around January 3 (perihelion) and farthest from the sun around July 3 (aphelion). The difference is minimal. The distance is about 93 million miles.

  • Our seasons are a function of the axial tilt. In Northern Hemisphere summer, the north pole receives 24 hours a day of sunlight for 6 weeks, warming the whole hemisphere. At that time, the Southern Hemisphere is having winter and the south pole is having 24 hours a day of darkness for the same 6 weeks. In Spring and Fall - around the equinoxes, the Earth is evenly heated and every where on Earth has 12 hours of day and 12 hours of night that day. Hence the name, Equinox. The winter effects on each Hemisphere are the opposite of the summer effects.

  • The tilt of the Earth is also responsible for the length of the day changing throughout the year. In the northern hemisphere, the longest day in the is Summer Solstice, about June 21 and the shortest day is Winter Solstice about December 21 with the Equinoxes at March and September 21 or so every year.

  • The tilt is also responsible for the apparent change in where the sun appears to rise. In Northern Hemisphere summer, the sun rises far to the northeast and sets far to the northwest; in winter it appears to rise southeast and set southwest. At the equinoxes, it appears to rise due east and set due west.

  • The moon orbits the Earth between five degrees north and south of the equator, crossing that line twice a year. That is why in Northern Hemisphere summer, the moon appears to ride low in the sky (it is in the southern hemisphere itself) and in Northern winter, the moon appears high in the sky. It is the opposite of the sun which rides high in summer and low in winter.

Here are some other factoids about our planet:

  • Earth rotates on its axis about once every 24 hours and revolves around the sun about once every 365 days. The speed at the equator is about 1040 miles per hour.
  • Northern Hemisphere is 50 percent of the land -- the Southern is 75 percent ocean.
  • Average land height is 0.8 kilometers
  • Average ocean depth 3.8 kilometers (3800 meters)
  • Lowest point - Marianas Trench 11,000 meters
  • Highest point - Mt. Everest 8936 meters
  • Molten magma, hot rock in Hawaii'an volcanos can reach 3000 C or 300 times boiling water.
  • Before artificial lighting, it was possible to see sun shadow, moon shadow and the shadow of Venus and bows on both the sun (rainbows) and moon under certain atmospheric conditions.

The direction of Earth's spin controls the directions of winds and waves.

  • At the Equator to 30 degrees N or S, the winds run away from the spin (easterlies).
  • In the mid-latitudes from 30 to 60 degrees N or S, the winds run toward the spin (westerlies).
  • In the polar latitudes, the winds again run away from the spin (easterlies).
  • The direction of the prevailing winds influences currents which flow away from the spin at the Equator and are deflected by continents towards the respective poles and back around to their place of origin.

Water is amazing stuff.

  • Unlike just about every other solid, the solid form of water (ice) floats which means it has a density less than that of its liquid phase.
  • Fresh water freezes at O Celsius (32 F) and boils at 100 C (212 F) at sea level. In both cases, its density becomes less than one.
  • Sea water is more dense than freshwater. The average density of seawater 1.026 g/cm3 while the average density of water 1.0 g/cm3.
  • Most water on Earth is salty (97 percent) leaving just 3 percent in glaciers and the other 1 percent in streams, lakes, groundwater and water vapor.

Pressure can do some unbelievable things.

  • Changing the pressure of a substance can change its temperature. Compression raises temperature, expansion lowers temperature.
  • The pressure of air at sea level is called 1 atm (about 100 g/cc or 14.7 lb/sq.in or 29.92 inches of mercury) . The instrument to measure barometric pressure gave rise to the terms "low pressure" and "high pressure." The air at sea level, being the most compressed, is usually the warmest and air gets colder as you go up. Half the air is in the bottom five miles of the 150 mile thick atmosphere.
    • At the surface of the earth, water boils at 100 degrees Celsius (212F) and freezes at 0 C (32F).
    • At higher elevations, water actually boils at a lower temperature, but takes longer to do it due to lower air pressures.
  • Confining pressure in the ocean rises 1 atm per 10 meters of depth + the 1 atm of air at the surface, so the pressure of air at the average ocean depth of 3800 meters is 381 atmospheres. Temperature at the bottom is variable and can be quite high near underseas volcanos.
  • Confining pressure in rock results in rock pressure increases of about 250-300 bars/kilometer and increases of around 30 degrees C/kilometer. Temperature, however, can vary based on nearness to volcanic activity.
  • Fluids tend to follow faults or cracks in rocks, upward towards areas of lesser pressure.
  • Minerals form in places with abrupt changes in pressure/temperature such as the air/water interface.

The U.S. should have already gone on the metric system. It would make it easier to teach because we wouldn't have to convert all the units between the two systems all the time. Learn to use metric.

  • 1 kilometer equals 0.62 of a mile; one mile equals about one and a half kilometers (1.6 km)
  • 1 inch is equal to 2.54 centimeters, therefore each centimeter is about one half inch.
  • 1 pint is equal to about one pound, one gallon of water weighs about 8 pounds
  • one kilogram of water equals one liter of water, also 2.24 pounds
  • there are, therefore 2 and one fourth pints in a liter
  • One gram of fresh water is equal to one cubic centimeter of water and also equal to one milliliter of water (1/1000 liter) at 20 degrees C (room temperature). Fresh water has a density of one gram/cc or 1.
  • Lead is one of the most dense materials on Earth. It has a density of about 12 g/cc.

The effects of organisms can and has affected Earth's atmosphere. In the earliest days of Earth's history, the atmosphere did not have much free oxygen. The Earth's oxygen was emitted as waste by colonial bacteria while they built huge colonial masses now called "stromatolites." Alternating layers of fine grained silica with iron oxides in several phases suggests winter clay or fine quartz runoff being recolonized every year by new iron-fixing bacteria. Their huge and deep deposits are mined for much industrial iron. Areas such as Iron Mountain, Michigan and areas in Western Australia have huge underground and open pit operations.

The organisms, however, changed the atmosphere and most were driven far underwater and underground where their descendents are in some places, still the dominant force on their changed Earth.

What has happened before can happen again.

Outline of Earth Science by Ellin Beltz

You are here
Part I
Atoms, Minerals, Rocks, Geological Time
Part II
Plate Tectonics, Earthquakes, Volcanos, Geological Structures
Part III
Fresh Water and its Landforms
Part IV
Part V

2005 by Ellin Beltz
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January 10, 2008