Fossils and Tectonic Plate Motion

Similar to ice cores, scientists can read about past climates and environments on Earth by studying the fossil record, which reveals clues about how organisms have changed and adapted to Earth’s changing climate. Fossils also provide evidence about past tectonic plate motion and how Earth’s surface has changed dramatically in the planet’s geologic history.

• In addition to ice cores, scientists also learn about past environments and climates by studying fossils—the remains of ancient animals and plants, the traces or impressions of living things from past geologic ages, or the traces of their activities.
• Fossils of leaves, twigs, and logs from large trees have told scientists that Antarctica hasn’t always been covered in ice.
• The discovery of certain plants on Antarctica provided evidence for the movement of Earth’s tectonic plates (drifting slabs of solid rock that make up Earth’s surface).
• The distribution of rocks and fossils, along with the shapes of the continents, provide evidence that Earth’s tectonic plates have moved great distances and reshaped Earth’s surface over millions of years.
• The fossil record includes all of the fossils that have ever been found. Scientists use the fossil record to understand Earth’s history.
• Scientists can determine a lot of information about a fossil based on which layer (strata) of rock it is found in, including its relative age and the environment in which it lived.

• Why was the discovery of fossilized plants in Antarctica important for understanding Earth’s climate?
• How did the discovery of the same kind of fossilized plants on Antarctica, South America, South Africa, and Australia provide evidence for the movement of Earth’s tectonic plates?
• Why does the shape of the continents support the idea that the continents were once joined together?
• Why are most fossils most often found in sedimentary rock?
• How can scientists use index fossils to determine a rock layer’s specific age?

Misconception: The Ice Age happened in the past.

Fact: We are currently in a warmer period within an ice age, and Earth has experienced multiple ice ages since it first formed.

Misconception: Glaciers don’t move.

Fact: The force of gravity constantly works on glaciers, causing them to move. Some glaciers move very slowly, but they are still moving.

Extinction: when a species no longer has living members in existence

Fossil : the remains of ancient animals and plants, the traces or impressions of living things from past geologic ages, or the traces of their activities

Fossil record : all of the fossils that have ever been found, which scientists use to understand Earth’s history

Index fossil : certain fossils known to exist in a particular time and place that may be used to determine the age of rocks or other fossils

Relative dating : the comparison of fossils in different rock layers to determine how old a rock or fossil is

Forests in Antarctica

Jane Francis is a scientist who has spent years exploring Antarctica. Her passion isn’t ice, however. She is fascinated by evidence suggesting that Antarctica was once covered by rainforests. This evidence is mostly in the form of fossils—the remains of ancient animals and plants, the traces or impressions of living things from past geologic ages, or the traces of their activities.

Francis and other scientists have found fossilized leaves, twigs, and logs that came from large trees in Antarctica. These fossils tell scientists that millions of years ago, Earth was much warmer. The glaciers and polar ice caps that currently exist were melted, and the land that is now covered in ice was a lush forest.

This discovery led to more questions. One big question was how plants could survive in the almost-total darkness of the Antarctic winter. Plants need sunlight to make their own food through photosynthesis. During the winter, plants in Antarctica would have had to rely on food they stored within their leaves and other structures. Scientists have been investigating how plants that once grew on Antarctica would have been able to survive in this near- darkness. For example, in one experiment, scientists grew plants in dark greenhouses. They discovered that the particular kind of plant they were testing was able to photosynthesize for 24 hours during the summer. This allowed them to store up large amounts of food.

Reading the Fossil Record

The best place to find fossils is sedimentary rock because of how sedimentary rock is formed. As layers of sand, soil, clay, gravel, and other sediment build up in one location over time, the pressure of the layers eventually compacts the sediment into sedimentary rock. The remains of living things can become trapped in the layers of rock that built up over time. These remains include whole plants and animals. They also include traces of organisms such as footprints. Over millions of years, heat and pressure turned these remains into fossils.

The fossil record includes all of the fossils that have ever been found. Scientists use the fossil record to understand Earth’s history. Only a very small percentage of living things ever become fossils because decomposition happens very quickly. Most of the past life that existed on Earth will remain unknown to humans. The story of life in the past comes from the small sample of fossils that have been collected.

Scientists have different tools for determining the age of a fossil. For example, if scientists don’t know the age of a fossil, they can compare it to other fossils. The comparison of fossils in different rock layers to determine a fossil’s age is called relative dating. Because of how they are formed, the fossils in lower layers of rock are older than fossils in higher layers. To determine a rock layer’s specific age, scientists use index fossils. Index fossils are certain fossils known to exist in a particular time and place. These fossils may be used to determine the age of rocks or other fossils. Because of this, they are sometimes called guide fossils. For example, a fossilized gastropod may have only existed between 130 and 140 million years ago (MYA). If the gastropod is present in a rock layer of an unknown age, it reveals that the age of the rock is likely to be 130 to 140 million years old.

For the main hands-on activity of this lesson, students conduct several investigations to analyze the relationship between the science phenomena of fossil distribution and tectonic plate motion. In the first section, students use a model that simulates sedimentary rock layers with fossilized organisms to analyze the relationship between the type of fossil organisms and their location in the rock strata model. In the second section, students create a supercontinent model based on the distribution of fossils and the shape of the continents.