CHICAGO (CBS) — Shock waves on the stock market as the three main U.S. indices suffered one of the steepest selloffs in years.

The Dow Jones Industrial Average plunged 530 points; the Nasdaq fell 171; the S&P was off 64.

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So, what’s behind the drastic drop–and what should you do?

A rocky day on Wall Street ended with the Dow diving more than 8 percent for the week–down from a record close just three months ago.

It has Tom McCann, who’s probably a lot like you, wondering if he’s walking on solid economic ground.

“I’m just a landscaper and a retired school teacher,” he said. “I have a little five and a three year old. I do have a 401(k), so you do keep an eye on it.”

Is there a reason to be panicked?

Robert Johnson, who studies world markets for Morningstar, says he doesn’t think so.

“I think it’s all related to China,” he said.

In recent days, China, the world’s second largest market, has devalued its currency. It manufacturing indexes dropped to their lowest levels in over six years.

U.S. markets were bound to feel some impact.

“A slowing in China is not a disaster for the U.S.,” Johnson said.

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In fact, Johnson sees a lot of positive in the U.S. economy.

The national unemployment rate has dropped to about 5.5 percent, considered healthy;

Existing home sales are at their highest pace since 2007; and

Oil, now below 40 dollars a barrel is at a 6.5 year low.

Even with today’s drops, the average portfolio of stocks remains flat for the year.

“So no particular reason to panic right now,” Johnson said.

That’s advice that a landscaper in the Beverly neighborhood tried to hold on to .

“That’s the nature of the market,” McCann said. “What goes up must come down right?”

The Dow has lost more than 1,000 points since Monday, that’s the largest weekly drop since October of 2008.

After years of upward growth and recovery, this may be so called correction many anticipated. The good news is the U.S. economy seems healthy enough to weather the storm.

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The advice at times like these is to think long term, so if you can handle the volatility of the market, don’t sell off.