Animation 17.1 Movement of Continents

INTRODUCTION

The continents on which we live are on the move, albeit at an average rate of only several centimeters each year. The continents move because they ride on top of gigantic plates that, in turn, float on a molten layer of Earth, called the mantle. Energy, released from radioactive decay in Earth's core, heats up the mantle and sets up convection currents that propel the plates around Earth's surface. The movement of the plates, and the continents that ride on them, is called continental drift.

At times in Earth's history, the continents have coalesced into giant landmasses, but at other times they have traveled away from each other. The positions of the continents affect Earth's climate, the sea levels, the distributions of organisms, as well as the birth and extinction of species. In addition to depicting continental drift, this animation also provides a summary of the state of life at each corresponding period in Earth's history.

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Textbook Reference: Key Concept 19.2 Major Lineages of Eukaryotes Diversified in the Precambrian, p.447

CONCLUSION

The changing positions of the continents have had dramatic effects on the Earth's climate and on its living organisms. For example, when the enormous landmass Gondwana formed over the South Pole 500 million years ago, the Earth entered a period of glaciation. Water became trapped in the frozen glaciers, which lowered the sea level dramatically. As the sea level dropped, continental shelves (submerged parts of the continents) became exposed, and the organisms that thrived there would have either died, adapted, or moved to other locations. The temperature of the oceans also dropped. During this time in Earth's history, 75% of marine species became extinct.

The positions of continents over time also explain some interesting features of the distribution of flora and fauna around the globe. For example, the island of Madagascar, currently near the southern tip of Africa, is home to animals that are remarkably similar to animals living in India. India and Madagascar are separated by 4000 km (~2500 miles) of ocean, much too great a distance for land animals to cross. However, at one time, India and Madagascar lay adjacent to each other. Until 90 million years ago, when India and Madagascar split, they could share species.