Merged Mining

Merged mining is a technique that lets miners secure two blockchains at once with the same proof-of-work computation, earning rewards on both without splitting hash power. The auxiliary chain accepts Bitcoin's proof of work as its own. Namecoin became the first merged-mined chain in October 2011, using a scheme called auxiliary proof of work.

Why it matters

Smaller proof-of-work chains struggle to attract enough hash power to resist 51 percent attacks. Merged mining lets them borrow Bitcoin's security budget: a miner builds a block template that commits to the auxiliary chain's block, and a solution good enough for the smaller chain's difficulty pays out there even when it misses Bitcoin's target. The miner incurs almost no extra cost beyond assembling a second template.

Critics note the model concentrates responsibility in Bitcoin miners who may not care about the smaller chain, and the auxiliary chain still needs its own nodes to validate its rules.

In the gold vs bitcoin debate

Merged mining shows that proof-of-work security is an economic resource that can be shared, much as gold's monetary credibility historically anchored paper currencies issued on top of it. Sidechains such as Rootstock use merged mining today, extending Bitcoin's security to applications the base layer does not support directly.