Sam: Which direction is up? This might seem like a silly question, but the answer isn't always obvious.

A river flows by a steep rocky hill. Layers of rock in the hill run vertical from top to bottom.

Sam: Rock layers can be tilted so much that the older layers are on top.

Looking upwards more layers of rock run vertically from the ground towards the sky.

Sam: Geologists call these overturned beds. Luckily, geologists and paleontologists have several tools to figure out if layered rock has been overturned.

Several examples of tilted layered rock are shown.

Sam: One tool is footprints and track fossils. The top side of these fossils will look like a depression, while the bottom side will look like raised bumps.

A grey rock with two fossilized three-toed dinosaur footprints. The footprints are bumps emerging from the rock.

Sam: The cracks that form when mud dries out often get preserved in the rock record. When we find mud cracks in old rocks. We know that the cracks open downwards.

A red layered rock with a fossilized mudcrack. The top of the crack is wide and tapers down to a point at the bottom.

Sam: When ice melts over a lake or ocean and drops a large rock onto a layer of soft silts, this is called a drop stone. The layers underneath the falling stone get bent and deform. As the rock gets buried the layers on top remain flat.

Sam: Root fossils are one of the best ways to find up. Roots always grow from the top and spread downwards.

Sam: Another tool is graded bedding. This forms when mixed sediments fall rapidly into water. The larger sediments settle out first and the finer grained sediments cover them over time. This leads to a finer grain size towards the top.