China’s Alibaba Group is becoming a serious threat to Amazon.The e-commerce giant made its debut friday in one of the largest public offerings of all time. The IPO was priced at $68 per share, giving Alibaba an initial market value of about $168 billion. That exceeds Amazon’s market capitalization of $150 billion, Alibaba’s websites account for 80% of all online commerce in China and its sales are growing rapidly. But its revenues are still only a fraction of Amazon’s.Here’s a brief breakdown of the two companies and how they compare. (It was made before the IPO.)