Continental Change

Earth has not always looked like it does now. Two hundred and fifty million years ago, the continents were one big landmass known as Pangea (Pangaea). The Atlantic and Indian Oceans did not exist. The landmass was encircled by one large ocean. Over time, the landmass began to break apart. The large pieces of broken land drifted away from one another to create the continents we know today. The idea of this movement of land is known as continental drift. The timeline shows the movement of the land.

The timeline shows the continental drift on Earth across the Paleozoic, Mesozoic and Cenozoic periods. About 245 million years ago, near the end of the Paleozoic period, Pangea was a single landmass. About 135 million years ago, during the Mesozoic period, Pangea split into Laurasia and Gondwana. About 65 million years ago, at the beginning of the Cenozoic period, the landmasses further split into 7 continents. Today, the continents have moved further apart.

Studying fossils has helped scientists arrive at the theory of continental drift. Without oceans between them, landmasses were once connected to each other and organisms could easily travel from continent to continent. Similar fossils were found on continents that are now separated by huge distances. Four main fossil types—Mesosaurus, Cynognathus, Lystrosaurus, and Glossopteris—provide evidence for continental movement over time. The Mesosaurus was a freshwater reptile that lived before dinosaurs. Cynognathus and Lystrosaurus were land reptiles. They lived on land and could not swim. Glossopteris plants had large, bulky seeds. The diagram shows the fossil distribution of how the organisms could have existed when landmasses were closer together.

The diagram shows that fossils of the land reptile Cynognathus were found across South America and Africa. Fossils of the freshwater reptile Mesosaurus were found across South America and Africa. Fossils of the land reptile Lystrosaurus were found across Africa, India and Antarctica. Fossils of the fern plant Glossopteris were found across South America, Africa, India, Antarctica, and Australia.

Two-Part Question
Multiple Choice Question
The following question has two parts. First, answer Part A. Then, answer Part B.

Part A:

What evidence does the discovery of the Glossopteris provide?

A.
The five continents were once connected.

B.
Plants were once capable of moving.

C.
Ocean waters have evaporated.

D.
All plants can live in any environment.

Multiple Choice Question
Part B:

Which answer provides an explanation for the answer choice in Part A?

A.
Africa and America have different climates.

B.
The locations of the oceans have changed.

C.
Glossopteris plants had bulky seeds.

D.
Glossopteris fossils were found on all continents.

1 answer

Part A:

What evidence does the discovery of the Glossopteris provide?

A. The five continents were once connected.

Part B:

Which answer provides an explanation for the answer choice in Part A?

D. Glossopteris fossils were found on all continents.

Explanation:

In Part A, the presence of Glossopteris fossils across the continents supports the idea that these landmasses were once connected because the plants could not have spread over vast oceans in their current state.

In Part B, the best explanation for this choice is that the fossils were found on all continents, indicating that they were once part of a larger landmass where the conditions allowed for their growth and spread.