"At the very least, I think it does put valuation under a microscope. This is an area we've been able to tiptoe past and not worry about if other data's grabbing the headlines," said Jack Ablin, CIO of BMO Private Bank. "Earnings season forces us to focus on values, earnings and revenues, and if they're coming through flat or slightly above zero, that's just not the ingredients of a rally."
Stocks dropped Wednesday, with Apple dragging down the major indexes, after disappointing guidance and iPhone sales in its Tuesday afternoon earnings. The tech giant was down 4.2 percent and was responsible for half of the Dow's losses. The Dow closed down 68 at 17,851.
"I don't think the market's going to plunge right now as a result of (earnings). I just think it's one of the biggest headwinds the market faces this year," said Ablin.
Analysts have been concerned by a lack of revenue growth, but 55 percent of the companies beat revenue forecasts so far, according to Thomson Reuters.
Read MoreUS equities hold lower as tech earnings disappoint
Markets are also paying close attention to the selloff in commodities, with some traders clearly thinking the Fed might pass on a rate hike in September if the selling continues, reducing inflation. Oil was down more than 3 percent Wednesday and WTI futures closed below $50 for the first time since April 2.
Gold meanwhile fell below $1,100 an ounce, and it is now down 6 percent over the last 10 sessions—its longest losing streak in more than 10 years.
"It's hard to like anything. The dollar is so strong. it just cast a pall against all commodities," said Dennis Gartman of the Gartman Letter. Other metals and agricultural commodities were also weaker.
Read MoreUS oil futures break $50
"This is not one asset class. They're all acting on their own but right now, they're acting in concert, one to the other, the dollar being the large implication," he said.
As for stocks, Gartman said the market's poor breadth and narrow leadership makes equities look vulnerable.
"I would hesitate to make the leap saying that commodities are telling us that the world is going into the dinger, and that equities prices are going to sell off ... nonetheless the equities market doesn't act very bullish to me at all," he said.
Ablin said he expects commodities to become a contrarian buy, but not yet. "It's a trend we want to get out of the way of," he said.
Read MoreGold is doing something it hasn't in 20 years
Caterpillar, McDonald's and General Motors report before the bell, while Amazon.com's release is after the close.
Other companies reporting Thursday morning include Bristol-Myers Squibb, Celgene, Eli Lilly, Union Pacific, Freeport-McMoran, Janus, PulteGroup, Alaska Air, Kimberly-Clark, KKR, Southwest Air, Dunkin Brands, Under Armour, and Comcast, CNBC's parent.
After-the-bell reports are expected from Starbucks, Visa, Capital One, Juniper Networks, Stryker, Chubb, PMC-Sierra, Federated Investors and Athenahealth.