Older layers of rock are usually found deeper underground., New layers of dirt slowly build up over old layers over time., “This fossil is millions of years old,” said the scientist., The Law of Superposition explains how Earth’s layers form over time., Archaeologists dig carefully to study ancient objects, bones, and fossils., Volcanoes can cover the land with ash, smoke, and hot rock., After a flood, rivers sometimes leave behind mud and sand., Deeper rock layers are usually older than shallow layers: this helps scientists study history., Earthquakes, landslides, and construction can sometimes mix up the layers., Scientists ask important questions, such as, “Which layer is the oldest?”

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