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- When asked my age I sometimes say, “I'm older than dirt“. Even at my age that is a bit of an exaggeration. The average age of the Earth's surface dirt and rocks is 500,000,000 years.
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-. That is an average. Some of the oldest rocks found were 3,800,000,000 years old. The reason for new rocks being formed is the result of erosion and plate tectonics that erased most all the planets earliest landforms.
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-. However, there is a place where erosion and plate tectonics have not changed things in the same way. That is on the Moon. The Moon is Earth's crust that was splashed into orbit 4,500,000,000years ago.
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-. The changes on the Moon's surface were totally different than what happened on the Earth. The Earth had an atmosphere that had wind and rain erosion. At the same time an atmosphere protected it from small meteor impacts.
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-. Moon had almost no atmosphere. It had hot and cold but no weather that resulted. No atmosphere meant the moon was not protected from meteor impacts and cratering. Its surface did have volcanism and ground faulting. In fact, the earliest surface of the Moon saw so many impacts that the immense energy transfer melted the surface forming a global magna ocean.
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-. Low-density elements like aluminum floated to the surface. High density elements like iron sank deeper below the surface.
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-. To get an idea of Moon’s impact history analysis of crater ages is shown in the table below: This is for craters 1 kilometer in diameter or greater, some were hundreds even thousands of miles in diameter. Impacts are shown per each square kilometer of surface.
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--------------------------- Billion years ago ----------------- Impacts per km^2
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------------------------------- 4.5 ------------------------------- 1 per 1 km^2
------------------------------- 4.0 ------------------------------- 5 per 100 km^2
------------------------------- 3.5 ------------------------------- 4 per 1,000 km^2
------------------------------- 3.0 ------------------------------- 2 per 1,000 km^2
------------------------------- 3.0 ------------------------------- 1 per 1,000 km^2
------------------------------- 1.0 ------------------------------- 1 per 1,000 km^2
------------------------------- 0.25 ----------------------------- 1 per 10,000 km^2
------------------------------- today ---------------------------- 1 per 100,000 km^2
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--. You can see that the early Moon was seriously pelted by meteors. The Earth was as well at that time. Every square kilometer of the moon had a one kilometer or greater diameter meteor impact on its surface. Today this is less than one impact per 100,000 square kilometers of moon surface.
- Meteor impacts were not the only erosion on the Moon. volcanism was caused by heating due to the radioactive decay of uranium and thorium that melted parts of the mantle. This fresh magna rose up through fractures under the crater basins, erupting cased vast expanses of lava on the surface. Rapidly flowing lava cut winding channels and a flowing magnetic caused basins to sink.
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-. Most of the volcanic eruptions occurred between 4,000,000,000 and 3,000,000,000 years ago with 50 to 60 eruptions occurring each year. Most all these eruptions ceased 1,000,000,000 years ago. Also, 3,800,000,000 years ago impact cratering had rapidly declined by a factor of a thousand.
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-. You can count the cratering yourself on the website “ NASA Lunar Reconnaissance 0rbiter” images at www.moonzoo.org. The Moon will orbit Earth 250,000 miles away but these images will be form less than 400 miles above the surface of the Moon.
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-. Dozens of missions to the Moon have uncovered a lot of Moon history and evolution. But, what we have learned has also generated many more questions. The next major goal in lunar science is another moon landing. When will we go back? An announcement will be made shortly, stay tuned.
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RSVP, with comments, suggestions, corrections. Index of reviews available ---
--- Some reviews are at: -------------------- http://jdetrick.blogspot.com -----
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---- www.twitter.com , --- 707-536-3272 ---- Sunday, April 27, 2014 ---
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