Man has not been on the earth since the beginning of time to measure and record the changes in the earth’s climate. However, nature has done her part by leaving detectors that supply information about the early earth through:
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1. Radioactive dating—oldest rock about 4.1 billion years old.
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2. Tree rings—Accurate to about 10,000 years ago.
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3. Fossils—Environment and evolution.
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4. Ice Cores—Accurate to about 150.000 years ago.
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5. Ocean floor samples—Accurate to about 160,000,000 million years ago.
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6. Corals—Indication of changing sea level.
Now the question is why have these changes taken place?
1. Change of solar flux distribution on the earth.
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A. Evidence now exists that the shape of the earth”s orbit changes from round to elliptical in 100,000 cycles.
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B. The tilt of the axis of the earth changes at 40,000 year cycles.
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C. Precession (wobbling)—operates on a 20,000 year cycle. These factors effect the amount and intensity of the solar radiation received by the earth causing it to become warmer or cooler. We are presently the farthest from the sun.
2. Continental Movement.
It is now quite evident that the positions of the continents have changed over time. The fit of the landmasses if put together like a jig-saw puzzle, the location of fossils after connecting the landmasses, location of rocks in mt. ranges after fit, paleomagnetism and evidence of glaciers in areas now to warm to support this activity. These movements affect the heat exchange on the earth as we demonstrated earlier with the investigations with land, water, shiny and dark objects. If you look at fig. 5 you will notice that the landmasses are moving toward the northern hemisphere. This movement makes more land available near the poles for ice build up thus affecting sea level and temperature.
3. Environmental
As life evolved, the composition of the atmosphere changed. As carbon dioxide decreases in the atmosphere the earth becomes cooler, ice storage increases and sea level lowers. The opposite occurs when carbon dioxide in the atmosphere is increased. Increasing the water vapor in the atmosphere might stimulate cloud formation blocking out radiation from the sun and cause the earth to cool down. As the earth cools down, there is less cloud formation and a warming trend may begin. This cycle probably keeps repeating itself.
4. Changes in the Solar Constant
Changes in the solar constant or the output of light from the sun has increased with time. 30 million years ago we received 30% less heat from the sun.
