Seafloor spreading at midoceanic ridges is how scientists first discovered the periodic reversal of what?

More Questions:

Grits are typically made from what grain?

What Christian sect observes its Sabbath on Saturday?

Which car manufacturer was the first to include seat belts as a standard feature in their vehicles?

What controversial book did Germaine Greer write?

Freetown is the capital of which African country?

The Silicon Valley is located in what California valley?

The historic district of Haight-Ashbury is located in what US city?

What tree measurement do foresters usually make at 4 feet above ground level?

Which planet is orbited by the moon Charon?

What is the definition of the "Life Zone" around a star?

The 1977 movie "Saturday Night Fever" was based on what "New York" magazine article?

With what band did Gloria Estefan sing during the 1980s?

Who was the last Viceroy to India?

Who was assassinated by Leon Czolgosz?

Which scientist wrote the book "A Brief History of Time"?