In about a week, one of the most significant shifts in crypto’s history will happen when the blockchain Ethereum completes a software update known as “the merge.”

The merge, which is tentatively scheduled for Sept. 15, will drastically reduce Ethereum’s energy usage, making it much more environmentally-friendly than Bitcoin. The merge could also have a slew of far-reaching effects, for better or worse: it could crash or turbocharge the price of Ether; spur mainstream adoption or reduce confidence in crypto; lessen some security risks, or exacerbate others. Here’s what a layperson should know about the transition.

How Ethereum’s blockchain will work—and why it’s so important

To understand the merge, it’s important to understand why people use blockchains in the first place. One of the most important ideals of the technology is that no central authority can control it. Whereas a government might be able to manipulate a central bank to its whims, for example, a blockchain should be immune to that kind of pressure. It should be self-sustaining and dispersed in its power.

And for years, Bitcoin and Ethereum—the two biggest blockchains—have operated without controlling bodies thanks to a process called Proof of Work. In it, the blockchain is operated and safeguarded by “miners,” who approve new and valid transactions by solving complex math puzzles, and get rewarded for their efforts in the blockchain’s currency. The complexity of the puzzles is supposed to make it extremely hard for hackers or tamperers to game the system.

But solving these puzzles requires an enormous amount of energy. Miners have set up giant computing rigs all over the world that run day and night, solving these puzzles and guzzling electricity. Studies estimate that Bitcoin mining uses more power globally per year than most countries, including the Philippines and Kazakhstan.

The enormous energy usage of Proof of Work—which, again, is built into its design—has caused widespread criticism from environmental groups, especially as countries try to reduce their emissions in the face of climate change. Proof of Work also has design issues in terms of security and scalability, some engineers argue. So while Ethereum’s first developers started to build the network on Proof of Work in 2014, they were already toying with the idea of eventually switching over to a new, untested system called Proof of Stake.

In Proof of Stake, energy-guzzling miners are replaced by watchdogs known as “validators,” who deposit a significant amount of money (32 ETH, which is currently worth about $50,000) into the Ethereum network in order to be able to approve or deny transactions. Like miners, they earn money rewards for doing so. Under this system, a hacker or bad-faith actor would need to put an obscene amount of money into the system in order to game it—and in doing so, risk losing that money if they are discovered and kicked out.

Core Ethereum developers have been working on the transition diligently for years. But they’ve encountered numerous challenges that have forced delay after delay, and turned the merge’s status into something of a running joke. Developers have explained that updating what is essentially the network’s operating system is incredibly difficult, especially given that it will be up and running the entire time: it will be akin to swapping out a car’s gas engine for an electric one while it’s barreling full-speed down a freeway.

Potential positive effects of the merge

Developers hope that pulling off such a risky move will be worth it for several reasons. The first is environmental. Because miners will no longer have a financial incentive to run computers around the clock, the network’s energy usage will drop by more than 99%, according to researchers at the Ethereum Foundation. Mike Brune, the director of the climate change campaign Change the Code/Not the Climate, wrote to TIME in a statement that the merge is a significant step in the right direction, and that he hopes Bitcoin will take the same path. “With fires raging around the world and historic floods destroying lives and livelihoods, state and federal leaders and corporate executives are racing to decarbonize as quickly as possible,” he wrote. “Ethereum has shown it’s possible to switch to an energy-efficient protocol with far less climate, air and water pollution.”

This improvement in energy efficiency could be good for business. Many traditional companies and financial institutions have expressed trepidation about jumping fully into Ethereum due to its enormous carbon footprint. Vitalik Buterin, the founder of Ethereum, acknowledged as much in February, and actually encouraged skeptics to wait to use the blockchain until it was less environmentally damaging to do so.

Read More: The Man Behind Ethereum Is Worried About Crypto’s Future

If the merge goes off without a hitch, then corporate adoption could accelerate, especially by institutions with environmental, social and governance (ESG) mandates. Joe Lubin, a co-founder of Ethereum and the founder of the blockchain company Consensys, tells TIME that he’s talked with several “major financial institutions” who have been waiting until the merge to become “significantly involved” in Ethereum.

Many other potential users have stayed away from Ethereum due to its high fees and congestion. The network wasn’t ready for the sharp uptick in users it received in 2021, forcing some people to pay hundreds of dollars in transaction fees.

The merge won’t eliminate those fees, but Ethereum developers say that its completion will lay the groundwork for them to roll out new technologies to scale the network. The most crucial tool is called sharding, which splits the network’s data into smaller parcels, making the network faster and cheaper to use. Buterin said in February that sharding could eventually lower fees to around a nickel—and bring back many crypto users who had spurned Ethereum for other cheaper blockchains, like Solana and Avalanche.

“It’ll take time to get there, but it basically takes us into an infinite-transaction-per-second throughput architecture,” Lubin says. “It’s about to go internet-scale.”

Ethereum developers also believe that the switch to Proof of Stake will improve security and make the network more immune to attacks. A report by Consensys says that in order for an attacker to take over 51% of the network—which would allow them to re-write parts of the blockchain as they wish—it would require more than $11 billion.

But there are plenty of risks

But the merge also comes with significant risks. Ethereum served as the primary network for the frenzy of crypto activity that has emerged over the last two years, including in NFTs, decentralized finance (DeFi), and decentralized autonomous organizations (DAOs). If something were to go wrong in the transition, the well-being of all of those applications and organizations—which collectively handle more than $50 billion in user funds—would be in peril.

Lubin, for what it’s worth, predicts the merge will be seamless and glitch-free for users. “It will be like Apple upgrading your iPhone operating system overnight, and you don’t even know what happened when you get on your machine in the morning,” he says.

The merge could also cause a split in Ethereum’s user base. Given that Ethereum is decentralized, no one is forcing users to switch to the new system. If enough users or platforms decide to stick with an old Proof of Work version of Ethereum, then mass chaos and confusion could ensue over where the real value of tokens lies. Some Proof of Work miners have already signaled that they intend to resist the merge, and have started jumping back to an even older version of the blockchain, now known as Ethereum Classic.

Many of these miners, however, are simply looking out for their own bottom line, as they invested in mining equipment that will soon be useless to Ethereum once it makes the switch. Almost all other Ethereum users have indicated that they will switch over to the Proof of Stake chain, making a full-out civil war improbable.

“I think at least a temporary fork is likely: there’s an opportunity to make a quick Ether, and there are a lot of opportunists out there,” Lubin says. “But I can’t imagine wanting to build anything, or put anything of significant value, on a chain that has so many things that are fundamentally broken and abandoned.”

Finally, some people are worried that the merge will make Ethereum more susceptible to censorship in the midst of a larger battle between crypto and the U.S. government. Last month, the Treasury Department prohibited Americans from using Tornado Cash, a service that helps crypto owners protect their anonymity. Any user who interacts with a Tornado Cash-related address risks violating U.S. sanctions. A large-scale Proof of Stake validator, like Coinbase, then, might choose to censor any transaction related to Tornado Cash to comply with the government. Such an action would run counter to crypto’s decentralization ideals.

But Brian Armstrong, the CEO of Coinbase, said that he would rather his company shut down its staking operations than enable censorship. And Collins Belton, a prominent crypto lawyer and managing partner of legal firm Brookwood, tells TIME that he doubts the merge will have much impact on the U.S. government’s regulation strategies. “I don’t think the argument is likely to stick, to say that Proof of Stake is so fundamentally different that the U.S. government will shift its approach and will now start approaching validators,” he says. “I think it overestimates the government’s ability to really parse through these technical arguments.”

Read more: A New U.S. Crackdown Has Crypto Users Worried About Their Privacy

What happens next

For the last couple of years, Ethereum developers have been rolling out test versions of the merge, searching for glitches and vulnerabilities in their code. On Tuesday, the merge’s final test run, known as the Bellatrix upgrade, was activated successfully, clearing the path for the real thing. The merge is now expected to happen on Sept. 15, although a series of complex technical factors could postpone it once again. At that point, experts will be watching the market closely to see if old versions of Ethereum skyrocket in usage, or recede to zero. At any rate, next week, new chapters of Ethereum and crypto will begin.