Euro concerns plagued the markets today, as macro fears made investors forget last week's optimism over a better-than-expected earnings season. Spanish bond yields soared to 7.5%, demonstrating investors' lack of faith in the fragile country. The euro dropped to a two-year low against the dollar, and anxiety continued to build about Spain and Greece keeping current on their debt. The pressure on the European Central Bank to rescue the flailing countries is growing. As of 12:15 p.m., the Dow Jones Industrial Average (INDEX: ^DJI) had dropped 1.2% while the S&P 500 (INDEX: ^GSPC) fell almost 1.5%.

These macro fears outweighed what has been a largely positive earnings season so far. Of the 30 Dow components, 12 have already announced quarterly earnings. Investors caught a quick breather before the action heats up later in the week, as McDonald's (NYSE: MCD) is the only Dow stock that's reporting today.

McDonald's second-quarter profit fell more than expected, and the fast-food giant warned investors of slowing same-stores-sales growth in July. Unsurprisingly, shares plummeted 3.2%, making McDonald's the second-worst performer on the blue chip index behind Microsoft.

Hewlett-Packard (NYSE: HPQ) also looked hung over from the weekend, as shares fell 3%. The tech company has been reeling from falling PC sales and business spending on tech due to macro headwinds from Europe and slowing growth in emerging markets. HP will not release earnings until Aug. 22, although the announcement will likely reveal even more falling sales. HP's stock has been cut nearly in half over the past year.

One bright spot on the Dow was industrial equipment maker Caterpillar (NYSE: CAT), which rose 0.25% in anticipation of the company's earnings announcement on Wednesday. While the average analyst earnings estimate has dropped from $2.33 per share to $2.27, large dividend-producing stocks like Caterpillar tend to benefit when investors are nervous and desire safer options. At a market cap exceeding $50 billion and posting a 2.6% yield, Caterpillar looks quite attractive in a scary market.

Lucky for you, The Motley Fool has identified a few other rock-solid stocks on the Dow that make for great investments during hard times. Investing in an age of global uncertainty is nerve-racking, but these three stocks have highly sustainable business models built for the long haul. To learn more, claim your copy of our latest special report: "The 3 Dow Stocks Dividend Investors Need." It's yours -- for free! -- so be sure to claim your copy today.

Foolish intern Charlie Kannel owns no shares of the companies mentioned above. The Motley Fool owns shares of McDonald's and Microsoft. Motley Fool newsletter services have recommended buying shares of Microsoft and McDonald's. Motley Fool newsletter services have also recommended creating a bull call spread position in Microsoft. The Motley Fool has a disclosure policy. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. Try any of our Foolish newsletter services free for 30 days.