Shares in Amazon.com (AMZN, $2,785.58) popped at Thursday's opening bell in an otherwise down market after the e-commerce colossus said it would effect a 20-for-1 stock split and buy back up to $10 billion of its shares. The Amazon stock split will be the fourth in the company's history, and it follows on the heels of Google parent Alphabet's (GOOGL) own 20-for-1 split announced in February.