The dramatic drop in Alphabet’s share price is one of the biggest market events of the year. Understanding what caused the plunge helps readers see how quickly company decisions can affect even the richest investors.

On Thursday the stock tumbled 13%, erasing a record $500 billion from the company’s market value, as investors grew increasingly cautious about major technology firms’ spending on artificial intelligence, CNN reported. The single‑day decline was the second‑largest in Wall Street history, behind only Nvidia’s $593 billion loss last January.

According to Forbes, Larry Page’s fortune fell $31.5 billion to $235.9 billion and Sergey Brin’s fell $28.9 billion to $217.2 billion. Both co‑founders own roughly a 3% stake in Alphabet, so the share price slide directly reduced their net worth.

Alphabet’s cash flow turned negative $9.1 billion in the third quarter after the company ramped AI spending to more than $50 billion, according to its quarterly report released after the market closed on Wednesday. At the same time, earnings missed Wall Street expectations: growth in core search and advertising slowed, and operating income rose to $40.6 billion, still below the $43.2 billion forecast.