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Explorations of the Universe. How Did the Earth and Moon Form?. Ideas About the Early Earth Have Run Hot and Cold (Literally). To 1900: Early Earth hot. Only way to explain its internal heat 1900-1950: Radioactivity can explain internal heat, but concept of hot formation lingers
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Explorations of the Universe How Did the Earth and Moon Form?
Ideas About the Early Earth Have Run Hot and Cold (Literally) • To 1900: Early Earth hot. Only way to explain its internal heat • 1900-1950: Radioactivity can explain internal heat, but concept of hot formation lingers • 1950-1980: Earth need not have formed hot • Modern: Hot Early Earth was right after all
Cold Earth - Hot Earth (Again) • If Earth accreted, need not have been hot • Depends on how fast heat radiated away compared to impact rate • As planets get bigger, their gravity causes higher-velocity impacts • Also impact ejecta buries hot rocks • Early Earth was hot - had magma ocean
How Did the Moon Form?Pre-1985 Ideas • Fission • Co-Creation • Capture
Fission • Early Earth spun rapidly, became unstable, broke in two. • Moon should orbit in Earth’s equatorial plane • Can’t simply throw something from surface into orbit - it either falls back or escapes
Co-Creation • Moon should orbit in Earth’s equatorial plane • Moon is less dense and different in chemistry than Earth
Capture • Can explain why Moon orbits close to ecliptic plane. • Can account for why Moon differs in density and chemistry from Earth • Requires extremely stringent conditions to happen • Seems too unlikely
A New Hypothesis: Mega-Impact • In computer simulations of solar system formation, we don’t get nine big planets • First stage: hundreds of Moon-Mars size planets • Small planets collide to make bigger ones • Can explain numerous Solar System anomalies
A New Hypothesis: Mega-Impact • Can explain why Moon orbits close to ecliptic plane. • Can account for why Moon differs in density and chemistry from Earth • A capture requires extremely precise conditions - a collision takes no skill at all.
As Usual, In Any Area of Science, Gary Larson Gets There First
This is a more or less literal rendition of an early computer simulation
Earth would have been as hot as the Sun for about 10,000 years