What happened the whole 194,000 years before that?
A lot of this hinges on what one defines as a "civilization." The 19th-century "civilizational" model that places the Sumerians as "first" basically defines a "civilization" as having a bunch of specific cultural practices and technologies, including (depending on the definition used) writing, intensive agriculture (with irrigation and water management), domestication of plants and animals, permanent settlements, hierarchical and stratified societies (e.g. governments), and usually the building of megastructures (pyramids, ziggurats, etc.). This is sort of your "civilizational starter pack" according to this line of thinking, and this is where Sumer looks like one of the first, if not the first, place to combine all of these things together. This definition of "civilization" is, we should note explicitly, somewhat teleological in its nature: we are defining our modern industrial societies as being "civilized," and so we are reaching backwards across human history to say, "when did people start doing the things that (we think) led to us?"
So what were people doing before Sumer? Or, heck, what were people doing in places other than Sumer when Sumer was doing that? Because the world was, by that time, thoroughly filled with human beings. They were not just sitting around and grazing.
The answer is, they were doing lots of stuff, and lots of different stuff. They had complex societies, some of which were hierarchical, some of which were not. Some of which were, anthropologists think, seasonably hierarchical (e.g., you have a king-centered society in the summer, to organize the hunt; you have an essentially communistic society in the winter). Some of these peoples practiced forms of agriculture (including with wild varieties of plants, but also sometimes domesticated ones), some of these peoples were pastoral (they traveled with animals they cared for, like sheep). Some were "hunter–gatherers," but even that means a lot of different things if you are talking about, say, people who trap fish versus people who hunt buffalo versus people who hunt aurochs versus people who harvest acorns. These are all really different ways of producing food and there were many different social arrangements that could accompany them (though one should be wary of attributing all social relationships, mechanistically, as deriving from material food production).
There were even megalithic structures pre-Sumer. A few of these are justly famous, like Göbekli Tepe, a pretty impressive carved-rock complex in modern-day Turkey that is about 8,000 years old, that appears to be made by non-agricultural peoples who came together seasonably. There were also quite large structures made out of mammoth tusks in what is modern Ukraine, which also seem to have been seasonably inhabited. (By "seasonably" I mean only, the people who made or used them were not permanently settled in them, and would come together periodically to, apparently, use them for feasting and other kinds of ritualistic activities.)
And these are, of course, just the things we have evidence of. Most human activities in prehistoric times did not leave behind lots of evidence (most stuff degrades, and many environments degrade things faster than others), and what evidence there is can be pretty hard to interpret. The evidence we do have points to quite a rich variety of different ways of living in prehistoric times, and people who were no less sophisticated or clever than modern people.
Separately, for ~80% of that 300,000 years, homo sapiens sapiens was still located in Africa. The full details of how they were living there are very hard to reconstruct (at least, I've seen very little that tries to do that), but one should keep in mind that because homo sapiens sapiens evolved in Africa, that means that there were lots of things that co-evolved with it — which probably means it was pretty difficult. The number of human-targeting parasites, pests, predators, and so on in Africa is high as a result. (My favorite example of this human-specific evolutionary targeting, which is a "positive" targeting, is the honeyguide, a bird that evolved to show humans where beehives were, so that it could feast upon the leftovers after people opened them up. That is an impressively symbiotic relationship!) Once humans left Africa, they were the invasive species that often lacked much competition, and found it possible to absolutely dominate (and, in many cases, devastate and disrupt) environments outside of it, but prior to that one can imagine it was probably a pretty difficult existence. (And one should also keep in mind that until about 40,000 years ago, homo sapiens sapiens was not the only hominid competing in these spaces — Neanderthals, homo floresiensis, the Denisovans, perhaps more — were competing for similar spaces with homo sapiens over some of this time period.)
So anyway, a rough way to think about it is this. Structurally-modern (in terms of skeletons) homo sapiens sapiens evolved in Africa some 300,000 years ago. We don't know a whole lot about what they were doing from then until about 50,000 years ago, but we know that they had the ability to make stone tools and deal with fire and a lot of other stuff (which pre-date homo sapiens). About 50,000 years ago, we start to see migrations taking place out of Africa, we start to see evidence of complex human cultural activity (art, clothing, jewelry, burials, etc.) in the fossil record. (Whether that had to "evolve" separately from homo sapiens sapiens, or was there all along, I don't know if we really know. Some authors seem to treat this kind of "culture" like a separate "evolution," some do not.) Over the course some tens of thousands of years, people started spreading out over the planet. They lived a variety of ways, probably mostly nomadic, probably mostly hunter-gatherer, but they were complex, intelligent, thinking creatures so we can assume they probably "experimented" with many different forms of life, some of which would have been successful, some of which would not have been. Their migration patterns do seem to indicate that they were increasing in population and "spreading out" over time. During this time, the climate swung in some pretty impressive directions, so the physical world would not have often looked the way it does today.
Around 15,000 years ago, people in many parts of the world appear to change from a "food gathering" existence to a "food producing" existence. This is what is sometimes called the Neolithic Revolution, though it is tricky to call any set of widespread and very gradual changes a "revolution" and it depends where you want to mark these things off. But this is where we start to see evidence of widespread agriculture (mostly horticulture at first, "gardening" rather than "farming"), of stone monuments, of pastoralism (keeping flocks), of domestic animals and plants, and so on. The causes of these changes are still hotly debated, but it seems plausible that it is linked both to increasing human population densities (which will strain ecosystems in a strict "hunter-gatherer" mode), and major environmental changes (the end of the most recent glacial period, which would have radically changed the global climate). There are also some who argue that the true answer might lie somewhere less "material," e.g., there is an argument that many of these changes stemmed from whatever evolved in the brain to allow for what we categorize today as "religion." (This strikes me as interestingly speculative, but very speculative. For this kind of argument, see e.g., Lewis-Williams and Pierce, Inside the Neolithic Mind.)
Out of this Neolithic world, you start to have these "urban" permanent settlements that we call "civilization" appear some 8,000 or so years ago, in specific parts of the world. Traditionally the argument for "why this happened when and where it did" is that it is a product of geography (the places where this happen tend to be "environmentally circumscripted," in that there are limited areas of possible agricultural development, surrounded by area hostile to settlement — think of the Nile River Valley, precariously surrounded by desert — which makes these "learn to be much more productive in terms of calories, or die" sorts of places), and environmental-technical factors (all of these "centers of civilization" had water management issues, and it is argued that complex societies arose out of dealing with the technical and bureaucratic problems posed by managing water on a large scale).
There are issues with each of these simple, "material" explanations (they don't quite jibe with the archaeological record, for example — the large-scale water management infrastructure, for example, seems to either pre-date or post-date the formation of governments, for example). There is also an argument that these things we see are just a few of the many social variations that people in this time were experimenting with, and that we perhaps are only giving them as much attention as we do because a) these civilizations not only thrived, but actively drove other modes of existence near them out of existence, and b) because we trace our own origins to them (and so we bias our attention). But either way, you get the picture: stuff started to change, and in ways that seems to have been self-expanding. Writing is an example of this: writing emerged as a technology for aiding with complex bureaucracies (the earliest examples of writing we have are things like receipts and taxes), and eventually evolved into a very complex tool. Once you invent something like writing, for whatever reason, it opens up entirely new vistas for how you might use it as a civilization — literature, philosophy, religious texts, laws, chronicles, whatever.
Hi, as the other user suggested I’d recommend looking at r/askanthropology as I imagine this would fall under their knowledge base. I’d specifically like to link this thread that is related to your question here; the thread below has had a fairly healthy discussion at around 85 comments so it seems to have had good engagement.
