Before we dive into the details of Ethereum block architecture, we need to revisit the blockchain structure of Ethereum. In Chapter 1, Blockchain Basics, we learned that an Ethereum blockchain is a Merkle tree where the leaves represent execution states of a code. For the sake of simplicity, a finer detail was suppressed. The Merkle tree of Ethereum is not a binary Merkle tree, as we saw for the bitcoin blockchain. You see, binary Merkle trees are great data structures when it comes to authenticating information that is in a list format, that is, a series of data chunks placed one after another. For such a transaction tree, it really doesn't matter how long it takes to edit the tree after it gets created. This is because the transactions remain in a form of one frozen tree which can only keep growing.

Ethereum, on the other hand, is...