After being mined by the miners, an Ethereum block goes through several checks before it is considered valid; the following are the checks it goes through:
- All the ommers/uncles have to verify its identity, considering the PoW for the uncles is valid.
- The existence of the previous block and its validity
- The validity of the timestamp of the block, that is, the current block's timestamp must be higher than the parent block's timestamp. Also, the current block and the parent block should be less than 15 minutes apart from each other. All the block times are calculated in Unix time.
If any of the preceding checks fails, the block gets rejected.
