Meteors appear when meteoroid particles enter Earth's atmosphere at speeds of at least 11 km/sec. As they heat up due to friction with the air, they vaporize and the hot vapor trail is visible as a meteor. Meteorites are meteoroid particles that survive entry and land on Earth. Iron meteorites consist mostly of iron and nickel, while stony meteorites contain silicate minerals and some metal. Meteor showers can occasionally produce meteor storms when Earth passes through a dense stream of debris, producing hundreds or thousands of meteors per hour over a short period. Meteorites offer a rare window into the early history of the solar system, as some are over 4.5 billion years old.