Relative dating helps us understand the order events happened. The law of superposition states that in unaltered layers of sediment, the oldest layer will be at the bottom. This important concept helps geologists and paleontologists, who study rocks and fossils, use relative dating techniques to identify the ages of rocks and fossils. Relative dating determines the order of objects or events, without necessarily knowing the specific, or absolute, age of each.

Geologists and paleontologists work like detectives using clues to figure out what happened first and what happened next. Use the clues in the following picture to see if you can use relative dating, and the law of superposition, to solve a mystery:

You are called to a crime scene where a woman, Agnes Brown, was murdered in her home during the night. It rained, and the ground is full of footprints and tire tracks. By observing these clues and talking to the people living in the house and neighbors, you must figure out who the murderer is. You have discovered that:

• 1) Agnes Brown’s husband, Ben Brown, drives a car.
• 2) The maid, Lucy, rides a bicycle to workk.
• 3) The cook, Sam, rides a motorcycle.
• 4) The butler, Erik, walks to work.
• 5) The neighbor, George, has a dog, and visits often.

The murder must have been the last person to come to the house. Who did it?

What are fossils and where are they found?

Fossils are natural preserved remains plants and animals that provide evidence of life in the past. They can include plants, fish, mammals, and dinosaurs. Fossils can be found in soil and rock layers that are exposed at the surface in road cuts and rock outcroppings. Paleontologists work with land owners to get permission to dig at sites like the one in the above photo. A permit is needed to dig on state lands.

Squalicorax shark tooth fossil

Archelon, or giant sea turtle, once lived in the Western Interior Seaway that covered North Dakota during the Cretaceous Period. Sea turtle fossils are extremely rare in North Dakota. These turtles laid their eggs on land and were vulnerable to attacks by predators. These giants could grow up to lengths of 15 feet. The only one found in North Dakota came from near Cooperstown, ND.

×

Shale is made up of tiny pieces of clay and other minerals. When mud is compacted over time, it can turn into shale. This shale may contain fossils.