I don't know the specific Schwalbe Marathon tires but they use a proprietary material called SmartGuard. Personally, I've used Armadillo (from Specialized) and GatorSkin (from Continental) tires, both of which I was told contain a kevlar layer which resists punctures from sharp objects.
In my experience I only got one sharp-object puncture on either of these brands in over 10 years of riding, contrasted with much more frequent punctures on traditional rubber tires.
I think it is possible to make extremely puncture-resistant bike tires with modern materials, without particularly terrible tradeoffs. Materials progress is amazing. Although these are not used, for example in racing, because there is some performance tradeoff in increasing resistance.
I did look a little further on the manufacturer websites, and it looks like neither is literally kevlar, but both are forms of dense cut-resistant polymer meshes (some kind of nylon mesh for the Armadillo and some kind of polyester mesh and polyamide mesh for the GatorSkin).
There's some subtlety about the difference in materials that resist slashing versus those that resist stabbing; my impression is that it's easier to make the latter (you can get extremely effective cutproof gloves, for example for kitchen use, very cheaply, but stabproof vests remain expensive). The puncture-resistant tires are more akin to stabproof vests, which I think is the more challenging property to achieve.