Orphan, Uncle & Genesis Blocks Explained

Orphan, Uncle & Genesis Blocks

There are many different types of blocks in the cryptocurrency and blockchain technology space, but few people actually understand what they mean. This article is going to highlight and explain the different types of blocks in the cryptocurrency space that you definitely NEED to know.

The different types of blocks include:

  • Orphan blocks
  • Stale blocks
  • Uncle blocks
  • Genesis blocks

Orphan blocks are commonly associated with Bitcoin. They are valid blocks that meet all the necessary requirements needed to be added to the blockchain, but are however still rejected. Orphan blocks occur when two miners produce a block at similar times. This happens because the acceptance of a block into the blockchain by the nodes on a network does not happen instantaneously, therefore, another miner can in practise, solve for the same exact block. This causes a temporary split in the network as the nodes attempt to decide which block to continue building on. The block with the greater proof-of-work will be the one that the blockchain is continued to be built on-top of. The block with the smaller proof-of-work, is not chosen, and is referred to as the orphan block. An orphan block can also be produced if an attacker attempts to reverse a transaction.

Stale blocks are often used interchangeably with orphan blocks because stale blocks are successfully mined blocks that were not included main chain. Therefore, if you see the word orphan block or stale block, be aware they mean very much the same thing.

Uncle blocks are commonly associated with the Ethereum blockchain and are the equivalent of orphan blocks, but with a slight difference. Uncle blocks are still valid blocks that were mined, but  then rejected. However, unlike with an orphan block where miners are not rewarded for mining them, miners are in fact rewarded for mining an uncle block. The rationale for this is twofold:

  • Promote decentralization of mining by still rewarding miners for producing stale blocks. This facilitates for solo mining as there is still a potential for reward even if the block mined is not included in the main chain.
  • Improves the overall security of the chain because a larger aggregate amount of work is done once you factor in computing power needed for regular block and an uncle block. As a result, no computing power is wasted on stale blocks.

Genesis block, ironically last but certainly not least, is the very first block of a blockchain. It provides the foundation on which an entire blockchain is built on top of. The Genesis block for Bitcoin contains a message from its creator, Sataoshi Nakamoto. The message reads as: “The Times 03/Jan/2009 Chancellor on brink of second bailout for banks”. The interpretation of this is very much open, but serves as a fitting message for the Genesis block of Bitcoin. Which in some ways, is the Genesis block of the entire cryptocurrency and blockchain technology space.


My name is Bisola Asolo and I am a crypto enthusiast. I love reading and writing about anything and everything related to cryptocurrency and blockchain technology!

Make sure to follow me on Twitter: @BisolaOTAsolo, to get my thoughts on recent cryptocurrency developments.