How does the Block in a Blockchain look like?

Blockchain is simply a very long string of 1’s and 0’s. Every 10 minutes, a new block gets added to the chain. Hence, the name Block-Chain.

Block 170 is a special block. 

It contains the first ever bitcoin transaction between two humans. 

Using this transaction, Satoshi Nakamoto, the father of blockchain, sent 10 bitcoins to late Hal Finney. 

This is how a block 170 looks like. Let’s call this Hal’s block.

How does Hal’s Block look on a block explorer?

  • Step 1. Go to
  • Step 2. Enter 170 on the Search box and press Enter
  • Step 3. Note the header fields (marked with solid line on the image below)
  • Step 4. Note the Block Hash (marked with dashed line on the image below)

Let’s understand two key concepts – Nonce and Merkle Root

1) Nonce

The bitcoin miner is busy ‘solving a puzzle’. The solution is a number, referred to as the nonce. If he solves the puzzle before others he gets rewarded with bitcoins. If he is beaten, he gets nothing. It’s a race. The word nonce stands for number that can be used just once. If he is beaten, he validates the block mined by the other miner. If the block is valid he throws away everything he was doing to the bin, adds the new block to his local copy of the Bitcoin blockchain, and the whole cycle starts all over again.

Nonce is the proof-of-work.

2) Merkel Root

Merkle root is the top node of a Merkle Tree – named after Ralph Merkle who patented it in 1979. Let’s say we have six transactions in our block. We take the hash of the first transaction and also the hash of the second transaction. Then we take both hashes, concatenate the hashes, and hash it again. We do the same for transaction 2 and 3. Keep doing this, and soon we will get a tree-like structure.

The key to the immutability of the blockchain lies in the concept of the Merkle Tree. 

Excerpt from the book A Date With Blockchain