Bitcoin tumbled below $30,000 on Thursday, as the cryptocurrency continued its 2021 slide after quadrupling in value last year.The digital currency dropped 17% to $29,246.77, wiping out about $100 billion from the market, according to data from CoinDesk. It’s now down more than 30% since peaking at $41,940 earlier this month.The latest plunge, which comes without any clear reason, underscores the volatility of a currency that’s become a popular investment for day traders in recent years even as it still has limited real-world application. Bitcoin rose over 300% in 2020, closing the year right about where it sits currently.Ether, the digital currency that’s second to Bitcoin in total value, dropped even more on Thursday, declining 22% to $1053.80. It’s now 27% below its high from earlier this week, according to CoinDesk. Ether rose 471% last year.President Joe Biden picked Gary Gensler, the former chairman of the Commodity Futures Trading Commission and an ex-Goldman Sachs banker, to be the next chair of the Securities and Exchange Commission. Gensler taught about cryptocurrencies at the Massachusetts Institute of Technology, starting in 2018.WATCH: Crypto market sheds $100B as investors await Biden’s regulatory approachNominations are open for the 2021 CNBC Disruptor 50, a list of private start-ups using breakthrough technology to become the next generation of great public companies. Submit by Friday, Feb. 12, at 3 pm EST.