Ethereum is a decentralized, open-source blockchain platform that was introduced in 2015 by Vitalik Buterin. It serves as a foundation for creating and deploying smart contracts and decentralized applications (dApps). Ethereum is known for its native cryptocurrency called Ether (ETH).

Unlike Bitcoin, which primarily functions as a digital currency, Ethereum's main goal is to provide a platform for developers to build and deploy decentralized applications. These applications can be programmed to run exactly as programmed without any downtime, censorship, fraud, or third-party interference. Ethereum's blockchain is designed to support Turing-complete smart contracts, which are self-executing contracts with the terms of the agreement directly written into lines of code.

One of the key innovations introduced by Ethereum is its use of the Solidity programming language, which allows developers to write smart contracts and dApps on the Ethereum platform. Smart contracts are computer programs that automatically execute contract terms once predefined conditions are met. They enable a wide range of applications, including decentralized finance (DeFi), decentralized exchanges, non-fungible tokens (NFTs), and more.

Ethereum also introduced the concept of ERC-20 tokens, which are fungible tokens that can be created and exchanged on the Ethereum blockchain. ERC-20 tokens have become the standard for launching new cryptocurrencies through initial coin offerings (ICOs) and have played a significant role in the growth of the blockchain ecosystem.

However, Ethereum has faced scalability challenges due to its design, which led to high transaction fees and slower transaction times during periods of high network activity. To address these issues, Ethereum has been undergoing a major upgrade known as Ethereum 2.0 or Eth2. This upgrade aims to improve scalability, security, and sustainability by transitioning from a proof-of-work (PoW) consensus mechanism to a proof-of-stake (PoS) consensus mechanism.

Eth2 introduces shard chains, which will increase the capacity of the network, allowing it to process more transactions in parallel. Additionally, the PoS consensus mechanism will replace the energy-intensive mining process, making Ethereum more energy-efficient.

It's important to note that my knowledge cutoff is in September 2021, and there have been developments in the Ethereum ecosystem since then. Therefore, for the most up-to-date information, I recommend referring to official Ethereum resources and recent news.