Why does bitcoin use so much energy?

In mid-May 2021, billionaire Elon Musk sent a tweet that crashed the cryptocurrency market. The Tesla CEO announced the electric vehicle company would no longer accept bitcoin for purchases due to its huge energy consumption. So why does crypto-mining use so much electricity, and is there a sustainable alternative? CNBC's Nessa Anwar is joined by Ryan Browne to explain.
Wed, Jun 16 20212:38 AM EDT