Layer 1 (L1)

What Is a Layer 1 Blockchain?

A Layer 1 blockchain is the base-level network that operates independently, without relying on any other chain for validation, execution, or security. It maintains its own set of validators or miners, enforces its own consensus rules, and settles transactions directly on its own ledger. Bitcoin, the original blockchain, is the canonical example of a Layer 1.

The "Layer 1" label emerged as scaling solutions began building on top of existing chains. When the Lightning Network launched for Bitcoin and rollups appeared on Ethereum, the industry needed terminology to distinguish the base chain from everything built above it. The base chain became "Layer 1," and off-chain protocols became "Layer 2."

What makes a blockchain "Layer 1" is self-sufficiency: it does not borrow security from another chain. A sidechain has its own consensus but may rely on a parent chain for certain guarantees. A rollup executes transactions off-chain but posts proofs back to L1 for finality. The L1 is the foundation that everything else anchors to.

How It Works

Every Layer 1 blockchain combines four core functions into a single system:

1. Consensus: nodes agree on which transactions are valid and their ordering. Bitcoin uses proof of work (miners compete to solve cryptographic puzzles), while Ethereum uses proof of stake (validators lock up ETH as collateral).
2. Execution: the network processes transactions and updates account balances or UTXO states. This determines what the chain can compute and how fast.
3. Data availability: all transaction data is stored and accessible so that any participant can independently verify the chain's state.
4. Settlement: transactions reach finality, becoming irreversible. On Bitcoin, a transaction is considered settled after six block confirmations (roughly 60 minutes). On Ethereum, finality takes approximately 15 minutes under normal conditions.

The Blockchain Trilemma

L1 design is governed by the blockchain trilemma, a framework popularized by Vitalik Buterin. It observes that a blockchain can realistically optimize for at most two of three properties at once:

• Decentralization: many independent nodes can participate in validation with low hardware requirements
• Security: the network resists attacks, rejects invalid transactions, and protects transaction history
• Scalability: the network handles growing transaction volume without congestion or excessive fees

Bitcoin maximizes decentralization and security (tens of thousands of nodes, over 15 years without a successful attack) but processes only 3 to 7 transactions per second. Solana prioritizes scalability and security (thousands of TPS with sub-second finality) but requires powerful hardware to run a validator, limiting decentralization.

L1 Transaction Throughput

Raw throughput varies dramatically across L1 networks. These figures represent real-world performance, not theoretical maximums:

Bitcoin's low throughput is a deliberate design choice, not a limitation. Keeping blocks small and block times long allows anyone with modest hardware to run a full node, preserving decentralization. The trade-off is that scaling must happen on Layer 2 protocols rather than on the base chain itself.

Layer 1 vs Layer 0 vs Layer 2

The layered model describes how different protocols relate to each other in terms of security and functionality:

• Layer 0: the infrastructure that connects multiple independent blockchains. Protocols like Polkadot (relay chain connecting parachains) and Cosmos (IBC protocol) operate at this level, providing cross-chain interoperability.
• Layer 1 (base layer): the self-sufficient blockchain that handles transactions, consensus, and security on its own ledger. Bitcoin, Ethereum, and Solana are all L1 networks.
• Layer 2: protocols that process transactions off-chain for speed and cost efficiency, then post proofs or data back to L1 for final settlement. Examples include the Lightning Network for Bitcoin and Arbitrum and Optimism for Ethereum.

The key relationship: L2s inherit their security from L1. An optimistic rollup on Ethereum is only as secure as Ethereum itself. If L1 is compromised, every L2 built on it is also compromised. This is why L1 security is the foundation that the entire ecosystem depends on.

L1 Fee Models and Economics

Every L1 must incentivize participants to secure the network. The two dominant economic models are:

Bitcoin: Block Rewards and Fee Market

Bitcoin miners earn revenue from two sources: block subsidies (newly minted BTC) and transaction fees. The block subsidy started at 50 BTC and halves every 210,000 blocks (roughly every four years). After the April 2024 halving, the subsidy dropped to 3.125 BTC per block. Over 96% of all 21 million BTC has already been issued.

Transaction fees operate as a market auction: users bid for limited block space, and miners include the highest-paying transactions first. During periods of congestion, fees can spike significantly. As block subsidies continue to halve, the long-term security of Bitcoin depends on a healthy fee market.

Ethereum: EIP-1559 and Fee Burning

Ethereum's EIP-1559 introduced a two-part fee structure: a base fee (algorithmically adjusted per block and burned) plus a priority tip (paid to validators). The base fee increases when blocks are more than 50% full and decreases when they are less than 50% full.

The burn mechanism permanently destroys ETH, reducing total supply. During periods of high network activity, more ETH is burned than issued, making the token temporarily deflationary. Validators also earn rewards from block proposals and attestations, with a minimum stake of 32 ETH required to participate.

Upgrading a Layer 1

Changing an L1 protocol is deliberately difficult. Because the base layer underpins everything built on top of it, upgrades require broad consensus among developers, node operators, miners or validators, and users. Two mechanisms exist:

• Soft fork: a backward-compatible upgrade. Nodes that do not upgrade can still process transactions under the new rules. No chain split occurs. Bitcoin's SegWit (2017) and Taproot (2021) were both soft forks.
• Hard fork: a non-backward-compatible change. Nodes that do not upgrade follow the old chain, potentially creating a permanent split. The Ethereum/Ethereum Classic split in 2016 and the Bitcoin/Bitcoin Cash split in 2017 resulted from contentious hard forks.

Recent L1 upgrades illustrate the pace of change. Bitcoin's SegWit increased effective block capacity by roughly 1.7x and fixed transaction malleability. Taproot introduced Schnorr signatures for more efficient multi-signature transactions and improved Script capabilities. On Ethereum, the Dencun upgrade (March 2024) introduced blob transactions for rollup data storage, reducing L2 transaction costs by up to 90%.

Use Cases

Layer 1 networks serve different roles depending on their design priorities:

• Final settlement: L1 is the ultimate arbiter of truth. Once a transaction achieves finality on L1, reversing it requires attacking the consensus mechanism itself. This makes L1 the preferred layer for high-value settlements.
• Security anchor for L2s: rollups, state channels, and sidechains all derive their security from the L1 they settle on. Bitcoin's L1 secures the Lightning Network; Ethereum's L1 secures dozens of rollups including Arbitrum, Optimism, and Base.
• Censorship-resistant money: Bitcoin's L1 provides censorship-resistant value transfer that no single entity can block or reverse, making it a store of value and settlement network for nation-state level participants.
• Smart contract execution: Ethereum and other programmable L1s host smart contracts that power DeFi protocols, NFT marketplaces, and decentralized applications without intermediaries.

Why It Matters for Spark

Spark is a Layer 2 protocol built on Bitcoin's L1. It inherits Bitcoin's security and finality guarantees while enabling faster, cheaper transactions off-chain. Users can always fall back to Bitcoin's L1 through a unilateral exit if needed: the base layer acts as the ultimate safety net. This relationship between L1 security and L2 functionality is what makes the layered architecture powerful.

Monolithic vs Modular L1 Design

Traditional L1s like Bitcoin and Solana are monolithic: they handle consensus, execution, data availability, and settlement all on the same chain. This is simpler to reason about but limits how much each function can be independently optimized.

The modular approach, championed by Ethereum's "rollup-centric roadmap," separates these functions. L1 becomes primarily a settlement and data availability layer, while execution moves to L2 rollups. The trade-off: modular designs gain scalability but add complexity in how layers interact.

This distinction matters for evaluating different ecosystems. When someone says "Ethereum processes 100,000 TPS," they typically mean across its L2 rollups combined, not on L1 itself. Understanding what happens on L1 versus L2 is essential for assessing actual security and finality guarantees.

Risks and Considerations

Scalability Constraints

L1 throughput is inherently limited by the need for every full node to process every transaction. Increasing block size or reducing block time improves throughput but raises hardware requirements, pushing out smaller node operators and reducing decentralization. There is no free lunch: every L1 scaling improvement involves a trade-off somewhere in the trilemma.

Upgrade Coordination Risk

Because L1 changes require broad stakeholder consensus, critical upgrades can take years to deploy. Bitcoin's SegWit activation took over two years of debate before reaching consensus. A vulnerability discovered on L1 may be slow to patch compared to a centralized system, though the decentralized nature also means no single point of failure.

Ossification

As L1 networks mature and accumulate more value, the threshold for making changes rises. This is sometimes called ossification: the protocol becomes increasingly resistant to modification. For Bitcoin, many view this as a feature rather than a bug, as it makes the monetary policy maximally credible. For chains that need to evolve rapidly, ossification can be a constraint.

Security Budget Concerns

For proof-of-work chains like Bitcoin, long-term security depends on miners earning enough revenue to justify the cost of securing the network. As block subsidies decrease with each halving, transaction fees must eventually compensate. Whether the fee market will generate sufficient revenue remains an open question in Bitcoin economics.

This glossary entry is for informational purposes only and does not constitute financial or investment advice. Always do your own research before using any protocol or technology.