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"Hello! How long, theoretically, does it take for every surface feature on the earth's crust to be completely obliterated and renewed?
Or alternatively, pick a time period, say 100,000 years and estimate what percentage of the earth's (terrestrial and aquatic) surface features would still be visible or at least not eroded away completely or obscured by ash, sediment, subduction etc to a depth of say 2 meters. These are just suggestions, please use any estimate parameters you deem appropriate.
The question pertains to the possible existence of undiscovered civilizations.
Sounds like a class question. Usually these kinds of questions are asked in context, that is, in relation to a class discussion, where parameters were laid out. Or alternatively you may be trying to lay out the basis for a novel.
I don't think anyone has actually calculated how long total obliteration of all features would take. I have heard claims of previous civilization artifacts being found encased in geologic materials of great age, that would tend some to theorize that they came from previous civilizations the predated known historical civilizations and were part of a cycle of civilization, catclysmic event and destruction, de-evolution, and rise of civilizaton again.
How much time it would take depends alot on weathering, geologic events, such as volcanic eruptions and subduction at plate margins etc.
For EVERYTHING to be consumed as it were, it would take on the order of hundreds of millions of years. Now, the Canadian craton, the heart of the North American Continent contains some of the oldest rocks in the world. They have been eroded and glaciated but they are still there, and probably always will be. Other such areas exist and only the margins have been highly altered. The sediments and volcanics of the east coast were acreted to the craton margin and the sediments of the great plains, and Rocky Mountains all formed slapped onto the western margin of this core craton.
100,000 years would not be enough time to erase all traces of a previous civilization, since fossil remains would still be in evidence. We have found remains of our fossilized primate ancestors that are older than that.
Again it would depend on localized geological events. If I had to describe a world altering event that would at the same time eradicate alot of evidence of previous civilizations it would be a Volcanic event such as what formed the Deccan Traps. This was a long period of volcanism that deposited a thickness of volcanic basalt and ash that exceeded a mile in depth, over an area approximately 193,051 square miles (512,000kmsq). They occurred over a period of 30,000 years. This even is believed to have had a hand in the Cretaceous-Paleogene extinction event by alering the climate by release of sulfur dioxide in vast quanties. This is at odds with those believe that the Chicxulub impact event in the Youcatan Peninsula area was the real culprit, but since tectonic activities tend to occur in a action reaction type of pairing who is to say that the impact did not trigger the start of the other? They do after all occur on almost the exact opposite sides of the globe. I have no idea of their relative timing however, only that they both occurred at the end of the Cretaceous. I don't think this explaination would fly due to the descrete layer of ash containing radio-nuclides (iridium) at a level indicating an extraterestrial origin. In any case, one could make a case for a meteor impact, followed by widespread volcanic outpourings, of the Deccan Trap (Trappa...scandinavian meanings "Steps" from the flood basal layering.) nature and magnitude. The impact if large enough would cause tsunamis along coasts of the ocean it impacted in. Then say a resurgence of volcanic activity of almost every major volcano, a subsequent nuclear winter, massive erosion and redeposition of soil denuded of vegitation, widespread volcanic ash deposition etc all would serve to obscure evidence of former civilizations. However it would preserve a lot of evidence a la Herculaneum and Pompey, where not only bodies but structures and a massive trove of artifacts were preserved in the ash of a pyroclastic flow from Mt. Vesuvius. Don't believe the over the top presentation of the movie soon to be released called Pompey. There is no evidence that a tsunami occurred in fact the eruption would have caused a tsunami in the direction away from the city not towards it. Also the flaming volcanic bombs look more like a barrage of catapault projectiles. Pyroclastic eruptions are like Mt. Saint Helens, not like Mona Loa in Hawaii. They are pretty boring up till they explode, not in a flaming fireball, but in a roaring cloud of ash and super heated gas.
I hope this helps and sorry I could nto be more specific with regard to timing.