I thought Google always had ads, but at first they were clearly marked and always relevant?

Edit: I stand corrected. Ads were added later, but when first introduced they were clearly marked. I got my history wrong.

Nope, there were no ads at the beginning. It was a big deal when they announced AdWords. And the ads were unobtrusive and often quite useful at the beginning.

Google was quite vocal about clearly marking ads, in contrast to Overture, Yahoo, and others who mixed ads into search results in the late 90s / early 2000s. I think the period when Google lightened, then entirely removed the colored background that made it easy to identify ads was an inflection point in their fall from being a company that genuinely focused on users towards becoming just another megacorp run by profit-maximizing MBAs.

No, they had no ads for several years. AdWords were introduced in 02000, at which point Google had existed (initially as google.stanford.edu) for four years, since 01996, which was 40% of the amount of time the Web had even existed. I started using Google in probably 01998, when people on Slashdot got excited about how much better their search quality was than AltaVista, but it probably wasn't until 01999 that I switched over completely—at first AltaVista still had better coverage.

Nope. The slope has been slippery, but way back at the top of it there were zero ads on the page.

Not at the very beginning. But when they first added ads, they were clearly marked in the top with a yellow background (and they didn't take over the whole page), and on the righthand column (and they were clearly marked as sponsored links).

I'd have to dredge it up but someone put up a site that showed the visual changes to ads over the past 15 years, and they've become more and more indistinguishable from organic search results, and they've taken over more of the page.

A great visual history of enshittification, and also how "growth at all costs" capitalism leads to that enshittification. Google was still taking in money hand over fist in the mid 00s when they had a few, clearly marked ads, but capitalism demands the line arcs upwards no matter what.