Uncle blocks (also called Ommer blocks) have an interesting role on the blockchain. According to Investopedia:
In blockchains that use proof-of-work, ommer blocks are rejected blocks created at the same time as another block. The network can only choose one block to add to the blockchain. In the Ethereum blockchain, this leftover block was called an ommer block. In other blockchains, they are called uncle or orphan blocks, referring to the familial relationships used to describe block positions within a blockchain.
Ommer blocks are no longer an issue under the proof-of-stake mechanism introduced to the Ethereum blockchain in 2022, but blockchains that use proof-of-work still produce these extra blocks.
Investopedia goes on to explain that:
In a public blockchain like Ethereum and Bitcoin, it’s essential to use a method that ensures data within the blockchain is verified and added by consensus. It is equally important to keep data from being changed. Many blockchains use a data structure called a Merkle tree to accomplish this.
A Merkle tree establishes ancestral relationships for blocks of data. Information from previous blocks is included in new blocks, similar to DNA passed on between generations. This creates the concept of a parent, parent’s sibling, child, and sibling blocks similar to a graphical representation of a family tree.
These blocks are different from orphan blocks. “The difference between an uncle block and an orphan block is that the Ethereum network rewards its uncle block miners. In contrast, the Bitcoin network does not compensate/reward orphan block miners.” These blocks can be mined according to Alchemy.com who has a great article about it. They say:
How do uncle block rewards get mined? When miners of the main chain block reference uncle blocks, both the miner of the main chain block and the miner of the uncle block receive an additional reward.
Each block in the main chain can reference up to two uncle blocks, with each uncle receiving 1/32 of an entire block reward. The reward provided to the uncle block miner, on the other hand, declines over time.
Ommer or Uncle blocks can be viewed using your favorite block explorer.
Sources:
–Investopedia article from 2024.
–Alchemy Docs.
