Earth Science: Geology, the Environment, and the Universe

Chapter 21: Fossils and the Rock Record

Problem of the Week

Fact or Inference (Inference, What’s That?)

Fragments of Earth’s history are captured in sedimentary rock layers found around the world. Using the evidence found in these rock strata, geologists have constructed the geologic time scale—a timeline of Earth’s geologic and biologic history.

No human was present to witness this history, so geologists must take the actual observations or data that they have collected, and make assumptions based on that data. These assumptions are called inferences. Chapter 21 describes the methods that geologists employ to make inferences about the age of sedimentary rock layers and fossils. Collecting facts and making inferences from them are critical skills for scientists to develop in order to interpret their findings. In this problem, you will develop your skills of observation and practice making inferences.

Problem:

Let’s practice:

1. Do some brainstorming. Think of items/things for which it is important to know the age.


2. Discuss the methods you use to determine the age of each item.


3. Choose one item from your list for which you used its external characteristics to judge its age.

Clarification:

By determining an item’s age through the observations of its external features, you have used the same skills that geologists use to determine relative age and to make inferences about age based on their observations.

**Note: When we observe, we collect the facts. When we analyze the facts, we make inferences about what these facts suggest.

Try it:

Examine the picture below, make observations, and then determine what inferences can be made from the facts you have collected.

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Photo courtesy of Photographer: J & K Hollingsworth, Fish and Wildlife Service photo

FWS FIREFIGHTERS MONITOR PRESCRIBED BURN, FLORIDA PANTHER NATIONAL WILDLIFE REFUGE (NWR), FLORIDA. Controlled or prescribed burns are important tools used by managers of national wildlife refuges across the country to promote healthy vegetation benefiting wildlife. Periodic burning allows older, matted undergrowth to be cleared away. The new growth comes in much faster and provides better food and cover for a variety of wildlife.