NARRATION

This rugged Tasmanian coastline is rewriting the history of the Earth. The rocks here reveal how tiny Tassie helped shape the world.

Jacob Mulder

These rocks preserve a really fascinating story. They tell us that the Earth is dynamic, continents move around, they run into each other, they get rifted apart, they drift around the globe.

NARRATION

The geology of Rocky Cape sheds new light on an ancient past.

Mark Horstman

To my north is mainland Australia, but it hasn't always been this way. What if I told you that Tassie was actually once part of another continent that's now on the other side of the planet. People like to say, 'Well, Tassie's a little bit special.' Now geology is starting to explain why.

Dr Jacqueline Halpin

We want to put Tasmania on a map one and a half billion years ago.

NARRATION

We're going way back in time to a planet that looks entirely alien to what we know today. You may have heard of the supercontinents Pangaea and Gondwana, when the shape of today's continents started to become recognisable.

Dr Jacqueline Halpin

They're supercontinents that have existed in the last 500 million years. But what we're looking at here in Tasmania is taking a step back again into some more ancient supercontinents where the models are a little more difficult to really pin down.

NARRATION

Long before Gondwana in Precambrian time, there was a lesser known supercontinent called Nuna, more than a billion years before the evolution of land plants and dinosaurs.

Dr Jacqueline Halpin

When we're talking one and a half billion years ago, it's not an easy process to wind back the clock that far. So we really have to go with the secrets locked in the rocks.

NARRATION

Geological detectives Jacqui Halpin and Jack Mulder search for clues to place Tasmania on the world map of Nuna for the first time.

Jacob Mulder

A lot of the field work is trying to figure out what kind of environment these rocks were deposited in. Are we looking at rocks that once formed in the middle of a mountain belt? Are we looking at rocks that were once deep under water? Or are we looking at rocks that were in a setting similar to what we're seeing behind us now? We try to search for the clues in the rock record that is telling us about what these rocks were before they became rocks.

Mark Horstman

These are the oldest rocks in Tasmania. And we know that from tiny crystals called zircon inside them that work like time machines. And what they reveal rewrites our understanding of the Precambrian world, and shows that even these rocks are far older than we previously thought.

NARRATION

To unlock the secrets in the rocks, they're ground down to release the microscopic zircon crystals. Just like panning for gold, they separate the zircon from other minerals. The zircons are key to aging the rocks, but first you have to catch the crystals with a one-hair paintbrush and a steady hand.

Dr Jacqueline Halpin

It takes a bit of coordination, it's very easy to flick them off. And everything under the microscope is in reverse. So left is right and right is left. So that takes a bit of practice. And then, of course, we can't drop them in between. So I don't want to sneeze.

NARRATION

Then things get more high-tech. A cathodoluminescence microscope reveals layers inside the zircon grains, which indicate when they became part of the sedimentary rock.

Dr Jacqueline Halpin

We can have up to billions of years history within just a single grain. So potentially, this grain might record several different ages and we need to be mindful of that when we're using the laser to date these samples.

NARRATION

Zapping the zircon with a laser reveals what it's made of, including radioactive trace elements.

Jacob Mulder

Uranium is a very radioactive element. So it would decay to lead at a constant rate. So, we know the rate at which uranium decays to lead. So if we can measure the amount of lead isotopes and uranium isotopes in the zircon crystals, we can figure out how old they are and, hence, how old the rock is.

NARRATION

By measuring the ratio of uranium to lead isotopes with a mass spectrometer, the zircon acts like a clock.

Jacob Mulder

The laser's basically destroying our zircon here. So it's very high-powered, very hot laser, and it's vaporising the zircon, turning it into a gas. And the material that gets vaporised out of this hole that's forming gets passed into a mass spectrometer behind me, and then we can measure different elements within that zircon to get the age and geochemical information that we need.

NARRATION

And the answer takes them even further back in time than they expected.

Jacob Mulder

These rocks are about one and a half billion years old. So that's about 500 million years older than we thought they were before.

NARRATION

The lab data about the age and the source of the rocks is correlated with what we see in the outcrops.

Mark Horstman

For a sedimentary rock, these layers seem to be going all over the place.

Dr Jacqueline Halpin

Yeah. And this bed here, you can see the individual layers are dipping towards me, and then we go into some more horizontal flatbeds, and then in the bed above, that's covered in lichen, we can see that the individual layers are actually tilted in the other direction.

Mark Horstman

What does that tell you about what was going on at the time?

Dr Jacqueline Halpin

So, the bed down here that's tilted towards me, the water is flowing in this direction, towards me. Whereas the bed above, the water's actually flowing in the other direction. So we can use that information to decide which direction the sediment is being brought in from.

NARRATION

Putting together all the pieces of the puzzle and comparing their zircons with elsewhere, they found a close match for the origin of these rocks. And it's not from Australia, where you might expect.

Dr Jacqueline Halpin

What we were able to show is that the sediments look like they're being derived mainly from east Antarctica and also from North America.

NARRATION

It's a startling discovery that means Tasmania started out as a microcontinent in its own right. It's old enough to be part of the ancient supercontinent called Nuna, when what's now Antarctica and Australia was in the Northern Hemisphere.

Jacob Mulder

It comes down to a very interesting question, you know, how far back can you call Tasmania Tasmania as we know it now. So basically we think it started life as a thick pile of sand sandwiched between two much larger continents.

NARRATION

The further back in time we go, the less certain we can be about Earth's history, but they have a theory of what the Nuna world map looked like and where Tasmania was in relation to Australia at the time.

Jacob Mulder

Here we are on a sunny day one and a half billion years ago, and this is the supercontinent Nuna. We'll chuck Tasmania right up here, right near the North Pole.

Dr Jacqueline Halpin

So, here we've got something resembling modern-day North America, from about Arizona up to Alaska. Part of east Antarctica here, so the modern Transantarctic Mountains run down here, South Australia, northern Australia, Western Australia. So, at the time, Australia was partly fragmented. From about 1,400 million years ago, the plate started to rift apart. So we had a plate boundary forming down through here. And as the continents start to rift apart, this is when the sea makes its way up here and we have deposition of a marine basin, with the sedimentary rocks forming here.

Mark Horstman

Which are the rocks you're studying here right now.

Dr Jacqueline Halpin

That's right. So as the continent split apart and the plates moved, part of Tasmania would be found over here in Arizona and part will be left with Antarctica here.

NARRATION

It's thought the rest of Tasmania drifted across the globe to collide with the Australian mainland about 500 million years ago.

Mark Horstman

It's amazing to think that after massive tectonic shifts over more than a billion years, I'm left here walking on a shelf of rock in Tasmania that has more to do with parts of America and Antarctica than it does with the rest of Australia.

Jacob Mulder

North America and Antarctica are big players. So being able to piece and pinpoint those continents together right back to the very start of time just by looking at this tiny little fragment in Tasmania is pretty exciting.

Dr Jacqueline Halpin

Understanding that our continent is dynamic and the continents move, that there's a plate tectonic engine ticking away and always has been, so understanding what drives that and those sorts of cycles on a multimillion-year scale, it's just something fundamental about the Earth.

NARRATION

And as the dance of the continents continues, who knows what the Earth will look like in another billion years.