The start of the Earth-Moon system has been studied to show that this was an exceptionally violent event. One result was that Earth became the terrestrial planet with the highest average density. Another result was that Earth acquired enough mass and radioactive elements that it is expected to maintain a molten core region and magnetic field for the expected life of the Earth. Earth alone of the terrestrial planets was then able to develop plate tectonics as a long term energy release mechanism. The dipole magnetic field of the Sun reverses periodically, currently at the rate of about every 11 years, so that there was a magnetic braking action acting on the core of Venus that accounts for the slow rotation of that planet. A key result is that the impact event that resulted in the Earth-Moon system led to long term stability on Earth that allowed the eventual development of complex life forms on the Earth.
References
[1]
Giant-Impact Hypothesis, Wikipedia. This Article Summarizes Various Formation Processes for the Earth as Resulting from a Collision between a Pre-Earth and Another Impactor. 62 References Are Indicated. The Differences Have Little Impact Here Since This Article Deals with the Resultant Earth and Moon as a Coupled System.
[2]
Carroll, B.W. and Ostlie, D.A. (2007) An Introduction to Modern Astrophysics. 2nd Edition, Pearson, San Francisco, p. 350.
[3]
Application of Eq. 19.4 Yields a Roche Limit of 2.9 R Earth for the Earth-Moon System (Ref. 2, p. 724).
[4]
Johnson, B.W. and Wing, B.A. (2020) Limited Archaean Continental Emergence Reflected in an Early Archaean 18O-Enriched Ocean. Nature Geoscience, 13, 243-248. https://doi.org/10.1038/s41561-020-0538-9
[5]
Only a Subset of the NASA Entries Are Listed.
https://solarsystem.nasa.gov/planet-compare/
[6]
Hazen, R.M. (2012) The Story of Earth. Penguin Books, Chapter 7.
[7]
https://nineplanets.org/venus/.
[8]
Parker, E.N. (1958) Dynamics of the Interplanetary Gas and Magnetic Fields. Astrophysical Journal, 128, 664. https://doi.org/10.1086/146579
[9]
Rebecca, B. (2018) Plate Tectonics May Be Essential for Life. Quanta Magazine.
Lee, P. (2009) Plate Tectonics Could Be Essential For Life. AstroBiology Magazine.
Shannon Hall, Space (2017) Earth’s Tectonic Activity May Be Crucial for Life and Rare in Our Galaxy. Scientific American.
