The "Tilt" of Time

We know the immediate and visible devastation earthquakes can cause, and last month, after the earthquake in Haiti, we posted a set of projects that offer good background material and talking points for discussion of earthquakes and plate tectonics. What students may not realize is that the impact of a big shake does more than cause structural damage.

In fact, an earthquake can alter the tilt of the Earth to such a degree that the length of time in a "day" changes. The change is very small—we are talking seconds broken into millions—so small that our timekeeping methods of hours and days isn't effected. It is still fascinating to realize, however, that earthquakes can alter the tilt of the planet and that the amount of seconds in a day is not absolute.

Science Daily reported this week that research suggests that the February 27, 8.8 earthquake in Chili may have shifted the Earth's axis and shortened the day. With a projected change in axis of "2.7 milliarcseconds (about 8 centimeters, or 3 inches)," scientists have determined that the earthquake may have "shortened the length of an Earth day by about 1.26 microseconds (a microsecond is one millionth of a second)."

The following project ideas can help students talk about and visualize the importance of the degree of "tilt" of the Earth by examining the change of "seasons" on Earth:

• The Reasons for the Seasons (Science Buddies difficulty level: 4-5)
• A Matter of Degrees: How Does the Tilt of Earth's Axis Affect the Seasons? (Science Buddies difficulty level: 7-8)