Rare Earth: The Moon

I’m at home today with a sick child who decided she wants to watch science programs about the universe.  As a nerd that is fascinated by cosmology, this made me extremely happy!  One of the programs she wanted to see is called, “The Day the Moon was Gone”, which can be watched here.  What I found fascinating about this video is just how dependent the Earth is on the moon to support complex life, which I think is part of an emerging cumulative case that can be made for the Earth being fine-tuned for life.

The current hypothesis on how the moon formed is that a Mars-sized planet was flung to Earth by Jupiter’s gravitational forces.  Moon rocks and the Earth’s crust share oxygen isotope ratios not found anywhere else in the solar system.  This is evidence that the moon and Earth were either a single body or somehow came in contact with one another in such a way that they share surface material.

Plate Tectonics

The “impactor” hit the Earth while the Earth was still molten, which may have allowed just the right amount of iron to be added back into the Earth’s core.  If too much iron had been added, Earth’s gravity would be stronger making running, throwing, and growing more difficult, but probably not a life-ender for simple life-forms.  Not enough iron and the Earth would have cooled too quickly for plate tectonics to have formed, which would have preventing life from forming.  Plate tectonics are vital for life for the following reasons:

·      Plate tectonics created continents for life on land and shallow seas.

·      Gases released from volcanic activity and cracks in the crust created the atmosphere.

·      Plate movements cycle nutrients that make oceanic life possible.

·      Plate tectonics creates a silicate/carbonate cycle that regulates the Earth’s temperature and CO2 content.

Tides

The Sun is 400 times farther away than the moon, but has a strong gravitational pull on the Earth.  The moon is ¼ of the size of the Earth, which is relatively large for a moon; practically its own planet.  The large mass of the moon is needed to have enough gravitational impact to affect the Earth and to counter the impact of the sun’s gravity.  Without the gravitational influence of the moon, the sun would create large tidal bulges across the Earth that would create daily, world-wide, tsunamis. 

The factors of 400x distance to the sun and ¼ size of the Earth create almost perfect solar eclipse that was instrumental in determining the composition of the sun through spectrum analysis, and by extension, the composition of other stars in the universe.  The solar eclipses were also used to test the Theory of General Relativity in its infancy.  A slightly imperfect eclipse turns out to be perfect for learning more about our universe.

 Climate
It’s also believed that the impact from the moon gave the Earth its current tilt angle and rotation speed.  The tilt and slight wobble around the axis gives the Earth the four seasons.  Without the moon, the Earth’s tilt would wobble so much around the axis that the climate change would be too extreme and too fast for complex life to adapt; one area’s tropics would be tomorrow’s ice sheet.

While the Earth was still molten, the moon’s gravity caused a tidal bulge of lava, which created a drag on the Earth’s rotation causing it to slow down.  The result is Earth’s rotation slowed from 8 hours per day to 24 hours per day.  The faster rotation would result in stronger winds and violent storms, and also shorter day/night cycles which would be difficult to complex life to form.  A faster rotation would also cause the magnetic field to increase, which would result in less radiation hitting the Earth.  Conversely, too slow of a rotation would weaken the magnetic field and allow too much radiation into the atmosphere.

Heavy Metals

This isn’t related to the moon, but is an interesting piece of information covered in the video.  There was a period called the Heavy Bombardment, where the Earth and the moon underwent significant impacts from asteroids after the Earth had cooled to the point of having a hard crust.  This allowed heavy metals such as iron, lead, uranium, gold, etc, to be near the surface and accessible to humans.  If the bombardment had occurred much sooner, the Earth would have still be molten causing the heavy metals to sink to the core.  Much later and life would have been obliterated.  The Heavy Bombardment isn’t critical for life to form, but it has been critical in human life flourishing.

 

As Hugh Ross says, maybe this Thanksgiving we should say thanks for not only the food that sustains our lives, but also the moon.