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Name: Sue
Status: other
Grade: other
Location: NV
Country: N/A
Date: N/A


Question:
If the moon is moving away from the earth at approximately 1.5 inches a year,and the earth is approximately 4.5 billion years old. Then how far was the moon from the earth then? Would 4.5 billion years times 1.5 inches = miles from earth. The moon being 221,463 miles, how accurate would that be. The number of miles I come up with is not even close. A mile being 63,360 inches. That would make the moon part of the earth. When did the moon separate from the earth?


Replies:
Hi, you have just nailed an important theory right on the head. There is a very well supported theory that the current Earth and Moon were produced from the collision of two planets in the early development of the solar system. These two planets, let us call them proto-Earth and proto-Moon collided, mixed, and then coalesced into the current Earth and Moon, with the Moon steadily getting farther away.

Many different data support this theory. The fact as you have pointed out that they are moving apart (unusual since gravity should be bringing them together as is the case in other planet/moon systems), the unusual similarity in composition of the two bodies, the age of the rocks on both bodies, etc.

You have to imagine that the separation is not linear though. We can expect that the Moon is receding but at a decreasing rate. So, your calculations are not quite accurate, but it gets the point across.

Greg (Roberto Gregorius)
Canisius College


The assumption that the present "drift" in the Earth-to-Moon distance is likely flawed. There are a number of phenomena (e.g. tidal drift, solar effects to name just two of a much longer list) that can alter that separation spacing. There is at least one theory that proposes that the Moon was part of the Earth. So it is important to using present day data extrapolated back millions of years.

Vince Calder



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