system
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human
[Mass Effect] Would the Reapers've ignored Earth if we never found the Charon Relay?

I think first contact happened 27/29 years before Eden Prime, so what if Earth's space program took 35 extra years to discover the archives on Mars? 

Aside from the Yahg, who else could remain? Is it possible we'd have Vorcha on every world in the Terminus system, just like we've got tresher maws all over the galaxy? Would the Virtual Aliens be spared, or considered space faring AI?
gpt
Remember that it can take the Reapers a century or two to complete their "project". So Earth discovers the relay 35 years later... and ends up in the middle of an ongoing Reaper purge, too late to do anything about it. 

But that's besides the point. The Reapers' setup is meant to encourage Galactic civilisations to centralise. That's what the mass relays and the citadel are for. This means that as soon as the Reapers take over, which normally means they immediately take control of the citadel, they have access to the collected *data* of every species that made it to the citadel. 

And that data will include records on civilisations that are of interest, that might reach the citadel some day. 

It's not unlikely that Earth is on that list. 

Even beyond that -- once the Reapers are done, well, reaping, they may well travel through *every possible relay* to check on the local system beyond. 

They'd find Earth.