Layer 1 Blockchain
The base blockchain network that independently validates and records transactions without relying on another chain.
What is Layer 1?
A Layer 1 (L1) blockchain is a foundational, self-sufficient blockchain network that independently processes, validates, and records transactions using its own consensus mechanism, native token, and security model. Bitcoin and Ethereum are the most prominent Layer 1 blockchains; others include Solana, Avalanche, BNB Chain, and Cardano. Layer 1 blockchains face the 'blockchain trilemma' — the difficulty of simultaneously achieving decentralization, security, and scalability. Bitcoin prioritizes decentralization and security at the cost of throughput (~7 transactions per second). Solana optimizes for throughput (~65,000 TPS) with trade-offs in decentralization. To scale without compromising security or decentralization, Layer 2 networks are built on top of Layer 1s, processing transactions off-chain and settling the final state back to the Layer 1. All DeFi activity ultimately settles to a Layer 1, which serves as the source of truth.
Example
When a user swaps tokens on Uniswap deployed on Ethereum's Layer 1, the final transaction is recorded on Ethereum's main chain. If instead they use Uniswap on Arbitrum (a Layer 2), the swap is processed off-chain and the net result is periodically settled to Ethereum Layer 1 in a compressed batch. Ethereum's Layer 1 remains the security anchor for both cases.
Source: Ethereum Foundation — Layer 1