What are Coinbase earn rewards?

Could you elaborate on the Coinbase Earn rewards program? I'm curious to understand how it works and what benefits it offers to users. Specifically, I'd like to know if these rewards are in the form of cryptocurrency, and if so, what cryptocurrencies are offered. Furthermore, what are the criteria for earning these rewards? Are there any limitations or requirements that users need to meet? Lastly, I'm also interested in knowing if these rewards are transferable or if they have any expiration dates. Clarifying these details would help me better understand the Coinbase Earn program and its potential benefits.