How long would it take, after humans disappear, for all evidence of our existence to vanish?
Estimating exactly how long it would take for all evidence of human existence to vanish is difficult, as it would depend on a wide range of factors such as environmental conditions, material durability, and the type of evidence in question. However, we can provide a rough timeline for when certain types of human-made structures and objects might begin to degrade or disappear.

A few decades to a century: Many buildings and structures made of wood, plaster, or brick would deteriorate relatively quickly, succumbing to natural processes like weathering, erosion, and decay. Overgrown vegetation would also contribute to the degradation of these structures.

Hundreds of years: Concrete and steel structures, such as bridges and skyscrapers, would take longer to break down. However, without regular maintenance, they would eventually succumb to corrosion, structural fatigue, and plant growth.

Thousands of years: Some evidence of human existence, like stone monuments or structures (e.g., the Pyramids, Stonehenge), could last for thousands of years, depending on the local environmental conditions.

Tens of thousands to millions of years: Fossilized remains and certain human-made materials, like plastics and glass, could persist for much longer, potentially up to millions of years. However, they would eventually be buried by geological processes or break down due to weathering and erosion.

Billions of years: Certain human legacies, like radio signals we've sent into space or the remains of spacecraft on the Moon, could persist for billions of years, until they are eventually destroyed by cosmic events.

Ultimately, the complete erasure of all evidence of human existence would be a process that spans a vast range of time, with some remnants persisting far longer than others.