The Dow Jones Industrial Average and Standard & Poor’s 500 Index gave up all of their 2015 gains Thursday, only to be crushed further on Friday when Dow plunged over 500 points. The Dow, S&P, and Nasdaq on Friday all saw drops of more than 1 percent thanks to fears that China’s economy is stalling and will take the world with it. China’s manufacturing sector shrank at the fastest pace since 2009, the last year of the Great Recession.