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What the hell is blockchain, really? — Hands-on lab

Page 5 of 7 — Section 5 of 7

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5/7 — What the hell is blockchain, really? — Hands-on lab
Steps
  1. Open Sepolia Etherscan:https://sepolia.etherscan.io/ (testnet, no real value). This is a public block explorer—a read-only window into the chain. In the top bar you will see the latest block number (e.g., “6429183”); click it to open that block.
  2. In that block page:Note block number, timestamp, tx count, gas used, base fee, miner/validator, and the parent hash.
    • Block number
      The height in the chain (e.g., 6429183).
    • Timestamp
      When the block was included (e.g., 2024-05-18 12:34:56 UTC).
    • Tx count
      How many transactions are inside (e.g., 98 txs).
    • Gas used
      Total gas consumed by those transactions (e.g., 12,345,678 gas units).
    • Base fee
      Network-set minimum per unit of gas (e.g., 1.2 gwei per gas).
    • Miner/validator
      Who produced the block.
    • Parent hash
      Link to the previous block’s fingerprint (e.g., 0xabc1…7890).
  3. Click the parent hash:To go to the previous block. That takes you one step back in history; the block you came from should list this block as its parent. Repeat once more to view 3 consecutive blocks and notice how each child points to its parent.
  4. Open any transaction inside:One of those blocks. Note From, To, Value, Fee, Nonce, Status, and Confirmations.
    • From
      Who sent it (payer), e.g., 0x1234…abcd.
    • To
      Who received it (payee or contract), e.g., 0x9abc…7890.
    • Value
      How much was sent (e.g., 0.01 ETH).
    • Fee
      What the sender paid to get included (e.g., 0.00042 ETH).
    • Nonce
      The sender’s transaction counter to keep order (e.g., 7).
    • Status
      Whether it succeeded, is pending, or failed.
    • Confirmations
      How many blocks have been added after this one (e.g., 12 confirms).
    Toggle “Click to see More” to view “Parent Txn Hash” (if a call) and “Logs” (if present).
  5. Write 2–3 sentences:What would break if someone edited block (N-2)? Which fields would no longer match? How would explorers reveal it? If you want to see this visually, try the Blockchain Demo (tamper mode) at /demos/blockchain-demo/.
  6. Optional:If you have a testnet wallet, send 0.001 testnet ETH to yourself and open the tx on the same explorer to compare wallet UI vs explorer.
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