See also activity 2.2.1

Much of what scientists know about the relative ages of rock comes from the study of fossils. They give scientists clues about how environments have changed over time and can be used to determine what lived where and when. Fossils are found trapped in the layers of sedimentary rocks.

Certain fossils always appear before others. If a rock is younger or older than another, it will hold a certain set of fossils to prove it - microscopic remains of plants and animals, pollen.

Geologists also rely on radioactive elements in the rocks which they measure to determine how far they have broken down.

Some of the answers lie in the rocks on the land and the sea floor. The rocks tell us what past environments and climates were like. Scientists have found fossils of similar plants and animals on different continents, which suggest that the continents were once joined together.

Fossils of tree and fern leaves, wood, air breathing amphibians and fish that lived in fresh water and a reptile have been found not only in Antarctica, but also in neighbouring countries.

To understand something of the geological history of the Earth, we need to add the dimension of time. When we talk about recorded history, time is measured in months, years, centuries and tens of centuries. When we talk about geological history, time is measured in millions and billions of years.

The earth is known to be 4.7 billion (a billion =1000 million) years old. 4,700,000,000 years old!

• it takes about 10 million years for a mountain chain to be uplifted 3,000m (at 0.3mm/yr)
• it takes about 25,000 years for the Atlantic ocean to widen another 1 km (at 4cm/yr)

We usually talk about time using words like minute, hour, day, year or century. Scientists use special words to describe periods of the earth’s geological history. Words such as period (eg Jurassic, Cretaceous) and era (eg Cenozoic).

The theory of plate tectonics suggests that the surface of the Earth consists of a jigsaw of plates forming the land we live on and the sea floor, which can separate and move around on the Earth’s molten core. Different continents ride on these plates. Where they collide, volcanic activity is common. Where they pull apart, ocean floors and rift valleys form. About 180 million years ago, in Jurassic times the jigsaw forming Gondwana, became restless and started breaking apart Volcanic eruptions with huge lava flows occurred. Australia and finally New Zealand were the last to break away about 100 million years ago.

Until about 160 million years ago Antarctica was part of the huge southern hemisphere land mass known as Gondwana, linked to Africa, South America, India, Australia and New Zealand. Over the next 100 million years, Gondwana broke up and countries shifted to their present positions. The world climate began to get colder about 350 million years ago and glaciers and an ice sheet developed on Gondwana.

The past gives us clues about our future

About 80 million years later the climate warmed again. Forests of Glossopteris trees with insect life and small 4 legged reptiles (Lystrosaurus) lived 300-250 million years ago. Because neither of these species could cross oceans it suggests that Antarctica and the other continents were joined.

The fossil record shows us that at least 3 million years ago the climate of Antarctica was warm enough to support beech forests. The fossil leaves are similar to species found today in New Zealand, Tasmania and South America.

Gondwana moved around the globe and Antarctica’s climate changed as a result. Around 500 million years ago, during the Cambrian period, Antarctica was in the tropics and at its warmest ever.

Antarctica has not always been an isolated continent surrounded by ocean located at the bottom of the world. It was once part of a larger land mass that gradually moved south from the equator. The continents of the world have not always been the shapes and sizes they are. Scientists have been able to trace continental drift back 600 million years.

F LEARNZ BLM 9 Geological Timeline

F LEARNZ BLM 12 Geological Timescale

F LEARNZ BLM 21 Cape Roberts Glossary

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