The recession

No, not that recession. Although this is probably discussed elsewhere here I’ll throw it out anyway. If the earth is 3.5 billion years old why would extrapolating backwards the rate of lunar recession put the earth in contact with the moon in only 1.5 billion years? Would the rate change over time and not be constant?

“Constant” is a theoretical proposition, that applies to “point models” of planet calculations.

The actual earth, is constantly being interfered with, by comets and other collisions. Some can increase the spin. And of course at times the core has shifted enough to move the magnetic poles. Whether these events were caused by collisions is speculated upon, but the internal friction of the event surely slowed the spin.

So “constant” is not possible.

The Recession of the Moon and the Age of the Earth-Moon System at Talk.Origins is a page dedicated to explaining this subject. Apparently one major factor on the system are oceanic tides on Earth, and these in turn are affected by the shape of the continents and seas, so plate tectonics plays a role. The distribution of the land areas directly affects how fast the Moon is receding. Paleontological evidence–fossils of tidal sediments–provide direct evidence that the Moon’s rate of recession was considerably lower in earlier eras. Evidently the current configuration of the tectonic plates–and the article suggests that in the long run it may be sort of unusual to have multiple continents the way we do–allows for a rate of lunar recession that’s higher than the historical average over the last few billion years.

It’s almost tempting to ask one of the moderators to stick “of the Moon” on the end of the subject line here, because we have some professional astronomers around here who could probably go on about this topic at length, but who may not be bothering to poke their noses in to the thread because they think it has something to do with the GDP and unemployment. Meanwhile, all the econ types are coming in here all fired up to start discoursing learnedly about interest rates and the business cycle, then they say “The recession of the Moon? Oh. I don’t anything about that.”

Extrapolation of any sort is very, very misleading, and can cause you to make some collossal errors. Does anyone have Mark Twain’s calculation handy, on the length of the Mississippi? It’s one thing (although still risky) to extend a trend a few percent beyond the observed region, but here we’re looking at a few hundred years of data, and assuming that the same trend holds for billions of years.

I’d be happy to, if the OP requests it.

All I need to know about extrapolation I learned from Zeno of Elea.