The contribution has to be pretty substantial. And it can't be just one piece of work. The standards around these parts are something like 4+ papers (around 1 p

The contribution has to be pretty substantial. And it can't be just one piece of work. The standards around these parts are something like 4+ papers (around 1 paper per year for 5-6 years) preferably including one or two solid journal papers all in top-tier venues. Of course not everyone meets this standard but basically everyone gets close. That's a lot work. It's your full time effort for those 5-6 years, 6+ days per week, 10+ hours per day. What might not be clear above is that once you can do research on your own you're close to done, but to get there you have to do a lot of work. Sure. Best way to get an idea is to just look up previous theses. They're basically all available online. "phd thesis cs" on google is a good place to start and just filter out the non-top-tier departments. Although these days many people just take their publications, reformat them, and that's their thesis (this is more common in the US and much less common in Europe). This saves a lot of time and makes people a lot more productive.