Is Mina proof of work?

Could you elaborate on whether Mina utilizes a proof-of-work consensus mechanism? Given the recent advancements in blockchain technology, there's been a surge of interest in alternative consensus mechanisms. As an expert in the field of cryptocurrency and finance, I'm curious to know if Mina has opted for a proof-of-work approach or if it has embraced a more energy-efficient consensus mechanism such as proof-of-stake. Understanding the consensus mechanism employed by Mina is crucial for assessing its scalability, security, and overall sustainability.