Fossil finds: a fossil find offers clues about ancient Earth's geography.(EARTH: PLATE TECTONICS).

The muddy landscape of Seymour Island, Antarctica, is harsh and unwelcoming. It is summertime, but it's 0[degrees]C (32[degrees]F) and the only signs of green are the specks of lichen, or moss-like plants clinging to rocks.

Seymour Island is located at the tip of a string of islands called the Antarctic Peninsula. To get here, Ross MacPhee, curator of the Division of Vertebrate Zoology at the American Museum of Natural History in New York City, took a three-hour flight on a Hercules C-130 transport, a large military plane, from Argentina, South America.

MacPhee and his team camp here in large tents for one month. During this time, they scour the area for geologic clues to Earth's history.

ANCIENT EARTH

By studying geologic evidence, scientists have learned that Earth's surface has changed over time. As late as 120 million years ago, many of the landmasses that we identify as continents today fit together like two giant puzzle pieces: Gondwana in the southern hemisphere and Laurasia in the northern hemisphere. MacPhee explains that tectonic plates--giant rock slabs that make up Earth's outer crust--float on Earth's mantle, or thick layer of hot flowing rock. This movement has shaped and reshaped the landscape.

MacPhee is on the hunt for anything that might teach us more about the geography of ancient Earth. He hopes to discover fossils of animal species that once roamed Antarctica as well as distant areas of the planet during the same time period. When fossils of related organisms are found in two now faraway places, it tells scientists that these areas were likely connected long ago.

"We don't have a time machine, so we can only make informed guesses about what the planet looked like millions of years ago from the fossils of the plants and animals that once lived here," says MacPhee. This field of science is known as biogeography.

FOSSIL DISCOVERY

Present-day Antarctica is icy, and largely barren and isolated from other landmasses. But about 45 million years ago, things were different. Back then, Antarctica was a tropical paradise covered in lush plants and inhabited by ancient animals that are now extinct.

At that time, a river used to run through the area that is now MacPhee's camp, making it a prime spot for fossil hunting. "It is much more common to find fossils of land animals where there was once water," says MacPhee. "When the animals die, the carcasses are preserved more rapidly in the muddy riverbed than if they are left to decompose on the ground's surface."

After weeks of digging with spades and sifting through dirt with metal screens, the team made a rare find. It's a fossil of a tiny 1.5 millimeter (0.06 inch)-long tooth that once belonged to a shrew-like mammal.

After examining the specimen back in his lab in New York, MacPhee finds that the tooth resembles other fossils found in Madagascar, Africa, the West Indies, and North America. How did these ancient animals--that are possibly descended from a common ancestor--get separated by hundreds of miles of ocean? MacPhee says there are two possibilities. "It is likely that animals migrated, or traveled across land bridges that once linked much of the landmasses in the southern hemisphere but have since been separated by the motion of tectonic plates," says MacPhee. "Another, less likely, possibility is that the animals floated on rafts of vegetation."

MacPhee thinks the fossilized tooth he and his team found may have belonged to an animal related to tenrecs, animals that live on Madagascar, a large island off the eastern coast of Africa. But he still has more sleuthing to do before he is sure. MacPhee is returning to Seymour Island in February in the hope of finding a more-complete fossil of the ancient animal. He says: "I'd love to find a whole jaw this time!"

CHANGING PLANET

THE WORLD THEN: Earths plates are constantly on the move. This is how the planet looked 120 million years ago.

THE WORLD NOW: This is how the continents look today. How does this map compare with the one above?

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As plate tectonics slowly nudged South America toward North America, some animals island-hopped into new territory beginning about 10 million years ago. Then, about 3 million years ago, the Isthmus of Panama formed, sparking an even larger exchange of animals: armadillos and primates traveled north while saber-toothed cats, squirrels, and llamas moved south. You can see fossils of some of the larger mammals in the Lila Acheson Wallace Hall of Mammals at the American Museum of Natural History. For more information, ask your teacher or visit www.amnh.org.

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Find more fantastic fossils online. Visit: www.scholastic.com /scienceworld

PRE-READING PROMPTS:

* How many continents does Earth have? (Seven.) Do you think the planet always looked as it does now?

* What would be some of the challenges in planning an expedition to the Antarctic?

DID YOU KNOW?

* Antarctica was discovered about 225 years ago, but only in the last 70 years have people been exploring this frozen continent. Today, scientists from around the world go there to study geology, meteorology, paleontology, marine biology, ecology, mid more.

* The Antarctic Peninsula reaches much farther north than the rest of Antarctica. Its climate is much warmer and wetter than other parts of the continent, but it also gets some of the strongest winds and most-severe storms. This area has many more species of living things, including marine mammals and birds, along the coast. Inland, it has many varieties of grasses, mosses, and lichens.

* In 1959, the 12 countries* that were then active in Antarctic science signed the Antarctic Treaty. (*Signers in 1959 included Argentina, Australia, Belgium, Chile, the French Republic, Japan, New Zealand, Norway, the Union of South Africa, the Union of Soviet Socialist Republics, the United Kingdom of Great Britain mid Northern Ireland, and the United States.) In 1961 the treaty took effect, with the goal of creating a natural reserve devoted to peace and science hi Antarctica. Any member nation of the United Nations can join. There are now 46 signatories.

CRITICAL THINKING:

* Imagine you were hunting for fossils. Would you set up camp at the site of an ancient lake or at a site that was once an open expanse of land? (the site of the ancient lake, because carcasses are preserved more rapidly in muddy water than they are at the ground's surface)

CROSS-CURRICULAR CONNECTIONS:

ART: Have students research plate tectonics and learn about Pangaea, Gondwana, and Laurasia, as well as the current movement of Earth's plates. Have them create a 3-panel poster showing how the planet looked 225 million years ago, 120 million years ago, and 50 million years from now. Highlight the location of current-day Antarctica on each panel.

RESOURCES

* Get loads of facts about Antarctica from the Central Intelligence Agency: https://www.cia.gov/library /publications/the-world-factbook/geos/ay.html

* Take a virtual tour of Antarctica via the University of Chicago's Department of Astronomy and Astrophysics: http://astro.uchicago.edu/cara/vtour/

CHECK FOR UNDERSTANDING

DIRECTIONS: Answer the following questions in complete sentences.

1. What was the arrangement of Earth's landmasses roughly 120 million years ago?

2. What is the field of science that studies the geographical distribution of plants and animals?

3. Describe what Antarctica was like approximately 45 million years ago.

4. Why might Ross MacPhee plan to return to Antarctica in February rather than in July?

5. What two theories explain how ancient animals--that are possibly descended from a common ancestor--could get separated by hundreds of miles of ocean?

ANSWERS

1. Roughly 120 million years ago, all of the landmasses were joined together into two giant continents--Gondwana in the southern hemisphere and Laurasia in the northern hemisphere.

2. Biogeography is the field of science that studies the geographical distribution of plants and animals.

3. Around 45 million years ago. Antarctica was a tropical paradise covered in lush plants and inhabited by animals that are now extinct.

4. February Is summertime in Antarctica.

5. Animals may have migrated across land bridges that have since been separated by the motion of tectonic plates: a less likely possibility is that the animals floated from one landmass to another on rafts of vegetation.

Source Citation
Klein, Andrew. "Fossil finds: a fossil find offers clues about ancient Earth's geography." Science World 8 Dec. 2008: 14+. Academic OneFile. Web. 8 Nov. 2009. .

Gale Document Number:A190051548