Book Quotes: The Moon as a Counterweight

From Our Created Moon: Earth's Fascinating Neighbor by Don DeYoung & John Whitcomb (page 52):

Earth's seasons are due to the tilt of its rotation axis, relative to the plane of the solar system....Computer studies show that the moon stabilizes the earth's tilt angle (Ward and Brownlee, 2000). The nearby moon acts as a massive counterweight that holds the earth's spin-axis in place. With no moon, the earth's axis would swing erratically between 0 degrees and 90 degrees due to gravity pulls from the sun and other planets, mainly Jupiter. Seasons would then be unpredictable and much more severe. For example, an earth tilt substantially greater than 23 1/2 degrees could lead to a permanent freezing of the oceans and the end of all life. Computer models indicate that this wandering of the earth's axis without a moon would be gradual, occurring over thousands of years.