Fossils and Tectonic Plate Motion

Science background gives teachers more in-depth information on the phenomena students explore. Below is an excerpt from the science background section on fossils and tectonic plate motion.

Fossils

Scientists also learn about Earth’s past by studying fossils. Fossils are the remains of ancient animals and plants, the traces or impressions of living things from past geologic ages, or the traces of their activities.

Scientists have found fossilized leaves, twigs, and logs that came from large trees. 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, so they could store large amounts of food.

When scientists first discovered fossils of one kind of ancient ‘seed-fern’ tree in Antarctica, these fossils told scientists about more than past changes in Earth’s climate. They also provided evidence that Earth’s surface has looked dramatically different in the past. The same kind of ancient seed-fern tree that scientists discovered on Antarctica were also found on South America, South Africa, and Australia. Scientists believe that these similarities occurred because millions of years ago, the continents were once joined together in a massive supercontinent called Pangaea.

Over millions of years, the plates underneath the continents kept moving, eventually breaking apart the landmass into the seven continents that exist today: Africa, Antarctica, Asia, Australia, Europe, North America, and South America.

Fossils also tell scientists about past environments on Earth, as well as the kinds of organisms that were able to survive in those environments. Whenever a dramatic change occurred to the planet, living things had to either adapt to the changes or die out. For example, the Great Ice Age did not happen overnight. It took many years for the planet to slowly cool and for glaciers to form. Animals and plants living on Earth had to slowly adapt to this change in climate.

As the temperature dropped, there was a decrease in the number of forests. Low temperatures mean less evaporation, so there was less rainfall to water plants. As trees died, open grasslands spread across the equator of the planet. Animals that fed on trees either died out or adapted to eating grass.

The cold also changed the appearance of animals. Cold- blooded animals such as lizards and snakes shrank in size and retreated to warmer areas of the planet. Warm-blooded animals were better able to survive, especially mammals, which grew bigger and hairier.

One famous ice age mammal is the woolly mammoth, which lived about 150,000 to 10,000 years ago. Mammoth fossils have been found in Europe, Asia, and North America. They grew about three meters tall and had thick coats of fur to stay warm, as well as layers of fat. They traveled in herds across the icy land, eating low-growing shrubs and grasses. Mammoths, along with most ice age animals, are now extinct. Extinction means that a species has no living members in existence.

Temperate animals, such as the elephant and rhinoceros, stayed in Southern Europe, Central Asia, and North Africa, avoiding much of the glacial chill and surviving through the present. Their cousins, the woolly mammoth and woolly rhinoceros, followed the expanding grasslands to the Arctic tundra, where they relied on their thick coats and other unique adaptations to survive. Most cold-adapted land mammals were relatively large in size, requiring them to consume large amounts of food every day. The woolly mammoth and its peers spent their days roaming over the snowy plains, foraging in packs.

Despite cold-adapted species’ success at surviving the cold, all that remains of most of these animals has been preserved as fossils. The cause of their extinction is debatable, but scientists believe it is due to a combination of hunting by humans, highly infectious diseases, and changes in food sources and geography as the climate warmed to present temperatures.