6. Exceptionally large Moon

Moon plays an important role for life on Earth because of its size. Compare to other planets, Earth has exceptionally large moon. The radius of Earth’s moon is 1,740 km whereas that of the Mars’ moon is only about 10 km. Because of its large size, Moon can stabilize rotation axis of the Earth and maintain tilt angle of about 23.5 degrees all the time. If there’s no Moon, Earth’s rotation axis will be wobbling and causing a severe climate change. Fig. 1.8 shows variations of rotation axis and ellipticity of Mars for the past 6 million years caused by not having a large moon.

Fig 1.8 – Variations of Mars’ rotation axis (top panel) and ellipticity (bottom panel).

Another important role of the Moon is producing tides (Fig. 1.9) that are essential for maintaining marine ecosystem on Earth. The tides mix nutrient-rich fresh water with sea water and provide nutrients to plankton that forms a basis of marine food chain. If we didn’t have a Moon, we couldn’t have ocean tides. If there’s no tides, sea water will be covered with red tides that will eventually wipe out most of marine life. If that happens, we won’t have any seafood such as salmon steak, fish cake, clam chowder, or lobster tail, etc.. Isn’t it irony we can not eat seafood if there's no Moon?

Fig 1.9 – Tides caused by Moon and Sun.

Fig 1.10 – Red tide caused by toxic plankton