For the second time in the past three trading days, the Dow Jones Industrial Average (DJINDICES:^DJI) fell more than 200 points, as disappointing quarterly results from major companies hurt the markets.

According to Bloomberg, 60% of the 33 S&P 500 companies reporting today missed analyst sales forecasts. The Dow fell 243 points, or 1.82%, to close at 13,102 on the worst single day of trading since June.

DuPont (NYSE:DD) was by far the biggest loser in the Dow, losing more than 9% on the heels of a terrible quarter where sales fell nearly 10%. DuPont also announced it was adjusting full-year profit guidance sharply downward and will cut 1,500 jobs from the workforce. In other words, the company came out with a perfect storm of bad news.

3M (NYSE:MMM) was the second-biggest loser in the Dow, backtracking more than 4% after it cut its projected income for the year. 3M, as a diversified conglomerate, is often seen as a benchmark of macroeconomic progress; it's not a good sign when the company lowers guidance.

Investors often try to protect themselves from uncertainty as much as possible. Today, uncertainty was everywhere, as the future leadership of the Federal Reserve itself was thrown into doubt. Reports surfaced that Ben Bernanke had told trusted confidantes that even in the case of President Barack Obama's re-election, he would not seek to reprise his current role as chairman. Though that won't be an issue until 2014, the fact that there is no clear successor didn't help markets regain their confidence.

Though we've started to hit a dismal patch in earnings season, Facebook (NASDAQ:FB) may turn out to be the knight in shining armor, at least until Apple (NASDAQ:AAPL) reports on Thursday. Facebook shares were briefly up almost 10% after hours, as the social-networking giant reported advertising revenues that far exceeded the expected numbers. Apple, on the other hand, announced its much-discussed new iPad Mini today; the company will release its quarterly earnings report on Thursday.