Archaeologists find ancient civilizations underground. How did they get covered? Is our current ground level higher than it was in the past?
—W. Brendel, Fayette, Ala. With certain notable exceptions, such as Pompeii, only abandoned fragments of past civilizations were buried by natural forces. People migrated and disseminated, leaving unwanted structures behind. Deserted buildings degraded from a lack of maintenance; plants overtook the space, died and decayed, building layers of soil over the centuries. Dust and debris from neighboring areas blew over the land, rains caused mudslides, storms toppled walls, earthquakes reshaped the local topography over time, and more.
Other fragments are sometimes found under modern cities, where earlier inhabitants slowly morphed into modern societies. In many cases, people found it easier or more economical to fill obsolete constructions and build on top of them rather than remove them. So they were purposely buried by humans.
Generally, what we find underground is far more valuable to us now than it was to the people who lived at the time.
Why don’t we feel the Earth spinning?
—Michelle H., Brandon, Fla. Because our atmosphere (which is held to the planet by gravity) moves along with us. Think of it like traveling in a moving railway car: The train is racing across the landscape, and so are we, but we don’t feel the effect of the high speed. Send questions to