How would the relics of extinct human society affect future civilizations?

Question

My story (same world as here) take place in a future Earth between 3 and 5 million years in the future. What kind of artifacts, if any, would civilizations from this era find from the now extinct humans? What tangible consequences would the Anthropocene have on their life and societies?

Random ideas on this topic:

• Ceramic will last indefinitely because of its molecular stability, similar to fossils in composition. Aluminum and stainless steel in tools (in cookware for example) will survive and so will (probably) plastic: the discovery of readymade tools could bring a sudden technological development and/or the emergence of a religious conscience to explain their presence.
• I expect plastic to be widespread, sometimes conserved in rock as a somewhat recognizable item and other times degraded to invisible dust (maybe even part of some newly evolved food chain?)
• Stone crafts and sculptures, like mount Rushmore, have a pretty good chance to survive the ages, even if terribly distorted by erosion and ice ages.
• In dry climates metals corrode but wood have a chance of being preserved.
• Streets and underground tunnels will collapse and they will probable became riverbeds in temperate climates. When the cities will inevitably crumble, mud and silt from these rivers will bury objects, tires, cars and even entire houses. In time mud will become rock and things will be preserved inside until maybe a river or a glacier will dig a canyon exposing the ancient buildings and relics.
• Structures in steel and reinforced concrete will crumble, be grinded and compressed under new geological strata, leaving this probably reddish layer rich in excellent quality metals (could be reused? Mined?).

Any other ideas?

EDIT: Rephrased the question to address a more specific topic;

DISCLAIMER: this question is different from What would be left of a civilization founded in dinosaur times? That question is about an imaginary society in the past with no interest on its influence on today human society, while my question is about OUR OWN society and how it will influence future civilizations. Things like the Pyramids or Mt. Rushmore can survive a few million years, so they are relevant artifact for the topic i'm talking about.

ALSO, 65 million years and ~4 million years is a really big time difference by all terms. Four geological periods have followed since 65 mya and an entire geological era has passed. Tectonics really plays a crucial role when talking about +65 millions of years; huge impact craters can be eroded, mountains rise and wear away, oceans are formed or vanish. Complex processes like the transformation of biomass in hydrocarbons can take place. My question revolves around a significant smaller time scale. The time frame i'm talking about would be entirely paced inside our own geological period. A difference of just a few millions years is important when talking of radioactive decay and the legacy of other human-related activities.

Answer 1

You need to be aware that four million years is significant in geological time. Ground level is not constant. In some places the ground is rising and in others it us falling. Human artifacts that are forced up will be weathered away over mere tens of millennia. Where ground level falls they will be buried and possibly preserved, but the burial may be a lot deeper than you expect. Almost everywhere, deeper than primitives will dig.

Consider London, which is sinking. The streets of Roman London are three to six meters below today's. Say two meters per millennium. Over a few million years that adds up to many kilometers.

So four million years hence there will be very little if any of our civilization visible at ground level. A pre-industrial people probably will not detect any sign that they are not the first people. Only when they start deep mining on an industrial scale and start a scientific study of geology will they notice our remains. The very occasional finds of technological fossils will probably be attributed to ancient gods or mythical civilisations like our Atlantis lying in the relatively recent past.

I expect initial discoveries will be hugely disputed, just as the existence of deep time, geological movement and drifting continents were fiercely disputed well into the 20th century.

Will their attainment of our levels of technology by hastened by the eventual mapping out of fossil cities? I doubt that anything would be well enough preserved to significantly advance their development. At this remove of time it would be far easier to see what we built, than how we built it.

Answer 2

A satellite high up in the atmosphere in a geostationary or highly elliptical orbit has the potential to stay in space for thousands, or even millions of years.