How Did a Piece of Canada End Up in Australia?

Did you know that part of Australia was once a part of Canada? Amazing, isn’t it?

This discovery was revealed by a team of geologists in a 2018 study. Geologists are often referred to as the historians of the Earth. They develop tools and techniques to unravel the secrets of the Earth’s history.

In this article, we will talk about supercontinents. We’ll learn how geologists use a technique called radiometric dating to study them. Then you’ll understand how geologists used this technique to discover a piece of Canada Down Under.

What is a supercontinent?

A supercontinent is an assembly of all (or most) landmasses into one very large continent. The lithosphere is Earth’s outer shell. Supercontinents happen when pieces of the lithosphere move over the Earth’s mantle and form one huge landmass. This happens because of plate tectonics.

Throughout geological time, there have been several supercontinents on Earth. The most recent supercontinent was Pangaea. It existed around 300 million years ago. Another supercontinent was Nuna, also known as Columbia. It formed about 1600 million years ago during the Precambrian era. 

Misconception Alert 

Pangaea is not the only supercontinent ever to have existed! But it is probably the most well-known supercontinent. 

What is radioactive dating?

Scientists use geochronology to study supercontinents. Geochronology is the study of the age of rocks. One geochronology technique is radioactive dating. It involves examining radioactive elements in rocks. For example, geologists using radioactive dating might study uranium, thorium, potassium, and carbon.

Some elements can have different numbers of neutrons. These are called isotopes. Isotopes can be stable or unstable. A stable isotope does not decay into other elements. An example of a stable isotope is ¹³C (carbon-13), which has 6 protons and 7 neutrons.

Meanwhile, unstable isotopes naturally decay in the environment. They change their atomic structure. This means they can gain or lose protons or neutrons. The original isotope is called the parent isotope. It decays into a daughter isotope. For instance, a parent isotope could be ¹⁴C, carbon-14, which has 6 protons and 8 neutrons. It can decay into ¹⁴N into nitrogen-14, which has 7 protons and 7 neutrons. You can learn more at this link.

All radioactive elements decay at a constant rate. This rate is called their half-life. The half-life of an isotope is the time it takes for half of the parent isotope to decay into the daughter isotopes.

This constant rate of decay acts as a clock. Geologists can use these clocks to calculate the age of a rock. They measure how many daughter isotopes have been generated. They also measure how many parent isotopes are left. 

Scientists can use isotopes with even longer half-lives to date very old rocks. For example, they might use the isotopes of Uranium (U-235 and U-238).

How did scientists use this technique in Australia?

Geologists studied sedimentary rocks in Georgetown Inlier, Northeast Australia. They measured small amounts of lead and uranium inside these rocks. Then they used the measurements to date the rocks. That’s how they made a fascinating discovery. These rocks have the same age as the Wernecke Supergroup. That’s a group of sedimentary rocks found in the Yukon and the Athabasca Basin in Canada! They were formed from the Laurentia supercontinent that existed 1.7-1.6 billion years ago.

The Georgetown Inlier rocks cannot be linked to any other rocks in Australia. Geologists think these rocks formed on the Laurentia continent and drifted apart around 1680 million years ago.  The drifting land may have collided with Australia when Nuna was formed. Much later, when Pangaea broke apart, the Georgetown Inlier remained with Australia.

The work of geologists

When scientists make a discovery like this, they still have to use other dating methods to cross-check the findings. Reconstructing the history of supercontinents is a difficult task. However, the historians of the Earth are working hard to achieve it. Geochronology is a useful tool to accomplish such a feat.

This discovery reminded me of my undergraduate degree in Earth Sciences. I worked in a geochronology laboratory. This fascinating field of study is something you can do too!