Rock Layers & Landscape Change Explorer

In undisturbed rock layers, the oldest layers are at the bottom and the newest are at the top.

This is because new sediment settles on top of older sediment over time.

• Bottom layer = formed first, oldest
• Top layer = formed last, youngest

• Sedimentary: formed from compressed sand, mud, and shells. Often contains fossils.
• Igneous: formed from cooled magma or lava. No fossils — too hot.
• Metamorphic: existing rock changed by heat and pressure. Fossils may be distorted.

• Sea floor: shells and sediment accumulate as limestone
• Flood deposit: rivers leave mud and silt that becomes shale
• Volcanic eruption: lava cools into dark igneous rock
• Desert dunes: wind-blown sand compresses into sandstone
• Glacier: ice and pressure transforms rock into metamorphic
• Erosion: wind and water remove rock, creating a gap in layers

Fossils are remains of ancient life preserved in rock. Where you find a fossil tells you what lived at that time and place.

• Marine fossils (trilobites, ammonites) mean a sea once covered the area
• Plant fossils (ferns) mean a warm, wet environment like a swamp or riverbank
• No fossils in igneous rock — the heat destroys organic material