The halving impact led to a decrease in fee income, and block subsidies became the main source of income for bitcoin miners. Of the $25.35 million miners earned per day on September 13, only $398,860 came from transaction fees, or just 1.6% of total revenue. This is a significant change from the previous period, when transaction fees topped out at more than 40% of miners' revenue. With block subsidies halving every four years, transaction fees will only grow in importance in cyber security, analysts say. Some advocate expanding block sizes to accommodate more transactions, while others advocate layer 2 solutions, which could push more settled transactions back to the main chain.