Back in 2009, the processing power required to mine bitcoins was relatively low. At the time, the first bitcoin miners used standard multicore CPUs to produce BTC at a rate of 50 per block. If you had a couple of computers lying around with decent specs, you could have earned bitcoins by mining them.
The first bitcoin miners used their CPUs to mine bitcoins, and Satoshi Nakamoto, the pseudonymous creator of Bitcoin, was the first to mine bitcoins on January 3, 2009. He mined the first batch of 50 bitcoins using his computer's CPU chip. This first bitcoin block was known as the Genesis Block.
As Bitcoin became more popular and the number of miners increased, the difficulty of mining increased, and the processing power required to mine bitcoins also increased. However, in 2009, the processing power required to mine bitcoins was relatively low, and it was possible to mine bitcoins using standard multicore CPUs.