The best responses to this month's "Big Question"

In our new issue, we asked a variety of experts and public figures to choose the most significant day in history. Their answers spanned centuries, from the day 65 million years ago an asteroid hit the Yucatán Peninsula, to the death of Ögedei Khan (December 11, 1241), to the assassination of Franz Ferdinand (June 28, 1914), to the day Hitler began Operation Barbarossa (June 22, 1941).

We posed the question to Twitter, too. This is a small collection of the best answers we saw.

Submit your own answer or suggest a question by emailing bigquestion@theatlantic.com.