Q: Why are crossbars on men's bikes different from those on women's bicycles? It should be the opposite. --Joan Rosenberg

Q: Artifacts are often found deep under the ground. Is this a sign that the earth is becoming fatter? --Dawn Evans

The Earth isn't expanding. Its surface is always changing. Historical artifacts may be buried by plate tectonics or surface processes. This could happen either suddenly (as in the eruption that buried Pompeii) or slowly over time. Due to the sea-level rise resulting from human-induced climate changes, Florida is becoming an historical artifact. --Elizabeth Cottrell (research geologist), National Museum of Natural History

Q: How did animals and insects evolve to play? --Stella S. Rogers | Sherman Oaks, California

Animal play is behavior that occurs without the use of a normal stimulus. The benefits of play have been documented in mammals, birds and reptiles, as well as fish. Larger animals may play to develop and engage their brains. Even small invertebrates are able to be seen playing. Some spiders will chase laser pointsers like cats, while others engage in play-fighting. These insects may be learning skills that will help them defend their territory, attract mates, or hunt prey. Because their neuroanatomy is so different to ours, it can be difficult to understand insect behavior. --Floyd Shockley is the National Museum of Natural History's entomology collection manager.

Q: Which science fiction author do you admire? --Paul Schatz | Havre de Grace, Maryland

This article is taken from Smithsonian magazine's June issue.