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The cryptographic puzzle is what makes miners put in effort and spend money on electricity. It also ensures that if any data is changed in any of the blocks, it immediately creates a chain reaction of invalidating all blocks that follow the altered block.
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The block consists of the hash of the previous block, the transaction data, and the nonce.
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Its main parts are, the previous block hash, transaction in the block, nonce and the current hash. 
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Donât forget about the transactions. 
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Not impossible. But very hard, at least in bitcoin. We have seen some other less secure networks getting successfully attacked. An example would be ETC (Ethereum Classic). You will learn more about attack later on in the academy. 
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A private key is never revealed publicly. We use the private key to make a digital signature, that miners can verify that the transaction is valid without actually us having to reveal our private key.
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Correct. Also keep in mind that the older blocks are safer than the newer one.
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No worries. You can always edit your post, by clicking the edit button. It is below you post and looks like a pen.
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I like how you answered the second question. Good job. Keep it up. 
Yes. It does get a bit more technical. But you mentioned the most important parts. I have seen your other homeworks. You are doing awesome!
While transaction are important, we must not forget about some other information such as: the hash of the previous block (enables the link), and the nonce (a number guessed by the miner).
The reward behind the puzzle is what incentivizes them, alongside with the transaction fees.
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Blockchain and Mining Homework
- It is important that the blocks are cryptographically linked together to ensure the security of the network. If something doesnât make sense the link is broken going forward. The only way it will make sense again I see to solve the puzzle.
- The block structure is comprised of transaction data, previous hash, and nonce numbers. The hash has to be lower than target number.
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To create security. Changes in the blockchain also change all blocks from then on, because each block needs to include the hash of the previous block. This is the linking. To temper with a part of the blockchain therefore requires tempering with it continuously, also re-mining all new blocks, until the fraudulent party succeeds in ahead getting of the whole rest of the network. This is so extremely difficult that itâs considered practically impossible (without controlling at least 51% of the network and then still itâs extremely difficult and risky).
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It includesâŚ
- Height (the block position number in the chain),
- the Nonce (the correctly guessed random number during proof of work, that together with the blocks hash needs to be equal or smaller than the target at the moment) ,
- the data (meaning the transactions / UTXOs to be confirmed at this very point),
- the hash of the previous block
- and also its own hash.
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- to ensure that previous blocks cant be altered without causing a âchain reactionâ.
- linked together ledgers of data.
Thank you, thanks for taking the time to respond!
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Why is it important that the blocks are cryptographically linked together?
To ensure the blockchain remains immutable. Any change in a block will be noticed by others in the network.
What does the block structure look like in bitcoin
Block 633495
Hash
0000000000000000000122b3e61c97059b7f36b4c945c553be06b27f38dcb214
Confirmations
52
Timestamp
2020-06-07 13:38
Height
633495
Miner
Number of Transactions
2,872
Difficulty
13,732,352,106,018.34
Merkle root
925f14346da260456b7bc2e02c2dcd6296af4cac2701a9714eb205e5d7b9ce2f
Version
0x20400000
Bits
387,219,253
Weight
3,992,842 WU
Size
1,227,955 bytes
Nonce
238,773,705
Transaction Volume
7792.52836995 BTC
Block Reward
6.25000000 BTC
Fee Reward
0.34280327 BTC
Copied and pasted from Blockchain.com
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The linking together of the blocks creates the integrity of the network and ensures security by making it near impossible to hack data in any block (blockchain is immutable).
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A block consist of its own hash, transaction data, the hash of the previous block and a nonce
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- Why is it important that the blocks are cryptographically linked together?
To maintain the integrity of all previous transactions. - What does the block structure look like in bitcoin?
The transactions for that block period
The hash of the previous block
a Nonce.
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That is how the blockchain structure looks like. What about an actual block? What is it composed of?
No problem. Keep up the good work. I am happy to see that we have more and more educated people in this space.
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