Earth and moon to scale:
Luna = 2159 miles diameter
Earth = 7918 miles diameter.
Which makes the impact of gravitational tidal forces from 240k miles away, that much more amazing.
Tidal forces raise and lower ocean levels by up to several feet every day, and stir Earth's molten iron core, keeping it nice and toasty, and giving us a magnetic field.
The magnetic field deflects deadly cosmic rays. Without it, mammalian life might never have evolved. So we probably owe our existence to Luna!
@sean The tide is caused by the Sun as much as the Moon. The effects of Gravity is cancelled out by the Sun and Moon. The water is "pulled away" from the Earth on one side (towards the Sun) and the Earth from the water on the opposite, causing both of the tides that occurs in one day. If the Moon and Sun are on the same or opposite side of the Earth the tides becomes more pronounced, that's why you have high tides twice a month.
@sean that sounds about right, just remember it varies a lot based on where in the orbit we are.
@ekg
According to this explanation, the sun's effect on tides is about half the moon's.
https://oceanservice.noaa.gov/education/tutorial_tides/tides02_cause.html