NEW YORK — A dizzying, brutal week of trading dropped one last round of harrowing swings on investors Friday.

After skidding sharply through the day as fear pounded markets, steep drops for stocks and bond yields suddenly eased up in the last hour. By the end of trading, the S&P 500 had more than halved its loss for the day to 1.7 percent and even locked in a gain for the week.

It’s the latest lurch in a wild ride that has sent stocks flipping between huge gains and losses — mostly losses the last two weeks. Investors are trying to guess how much economic damage the coronavirus will ultimately inflict, and they’re shifting by the minute as the number of new infections piles up on one hand and central banks and governments offer stimulus on the other.

All the uncertainty has left markets churning.

“It’s anyone’s guess at this point why it rallied into the close,” Adam Taback, chief investment officer for Wells Fargo Private Bank, said of the last hour of Friday’s trading.

Earlier in the day, the S&P 500 had been down 4 percent. Even more alarming was another breathtaking drop in Treasury yields to record lows.

The 10-year Treasury yield falls when investors are worried about a weaker economy and inflation, and it sank below 0.70 percent at one point. Earlier this week, it had never in history been below 1 percent. It was at 1.90 percent at the start of the year, before the virus fears took hold.

Even a better-than-expected report on U.S. jobs wasn’t enough to pull markets from the undertow. It’s usually the most anticipated piece of economic data each month, but investors looked past February’s solid hiring numbers because they came from before the new coronavirus was spreading quickly across the country.

At the heart of the drops is the fear of the unknown. The virus usually causes only mild to moderate symptoms. But because it’s new, experts aren’t sure how far it will spread and how much damage it will ultimately do, both to health and to the economy.

The number of infections has topped 100,000 worldwide and businesses are reporting hits to their earnings.