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BOB HIRSHON (host):
Why does the earth have a tilt? I’m Bob Hirshon and this is Science Update.
We owe our seasons to the earth’s nearly 23 and a half degree tilt. A Science Update listener called our toll free line—1-800-WHY-ISIT to ask what caused the tilt. NASA physicist Betsy Pugel says it all happened billions of years ago, when the Earth was just a baby planet.
BETSY PUGEL (NASA):
Long ago when our solar system was forming, you had lots of different things that were coalescing into spheres; those spheres ended up having orbits and sometimes run into each other. So it may be that once upon a time, earth didn’t have a tilt in its axis, but some major collision or collisions happened that—boop—that kind of tipped earth off of its axis.
She says some scientists think that without the resulting seasonal changes, life may not have formed on the planet at all. I’m Bob Hirshon, for AAAS, the science society.