From lush to dust: Nullarbor rocks reveal ancient climate variability

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Researchers in Washington state have discovered when the iconic Nullarbor Plain dried up and how it shaped the modern ecosystem.

The Nullarbor has not always been a dry, dusty plain. It may be hard to imagine, but it was once covered in lush forests with diverse flora and fauna.

Until now, geologists didn’t know when the terrain changed. But a new study from Curtin University reveals that the area he dried up between 2.4 and 2.7 million years ago.

This discovery provides insight into how modern ecosystems evolved.

“This is an important element for understanding the biogeography of Australia,” said Dr. Maximilian Dröllner, lead author of the study and PhD candidate in the Timescales of Mineral Systems group at Curtin University. increase.

high and dry

Millions of years ago, the Nullarbor was under the sea. It appeared gradually as the sea level dropped.

Dense forests thrived in a humid climate, although the groundwater table was still relatively high.

Nullarbor changes over time, causing species separation and the formation of goethite-rich rocks | | Dr. Maximilian Drerner

“Fossils tell us that there were animals and plants that are extinct today,” says Max.

Two of the world’s largest cuckoo birds and a kangaroo are just a few of the extinct animals that once called Nullarbor home.

When the water table dropped dramatically, the drylands we see today formed.

compelling evidence

Max and his team analyzed iron oxide in rocks buried 20 to 30 meters below the surface of the plain.

Iron-rich rocks contain minerals that are indicators of past groundwater levels. This makes it an excellent archive of historical changes in climate.

“We used the ones that were dried directly on the continent,” says Max.

How did they measure what was in the rock? They fired a laser.


Conventional climate dating models rely primarily on marine sediments.

“They are often continuous layers, so you can pinpoint the age,” says Max.

Although this method shows broad global changes, it is not specific enough to pinpoint local environmental changes with precision.

“If you really want to understand how things have changed locally, you need a local product,” says Max.


When iron-rich water comes in contact with oxygen, goethite, a mineral that is the main component of rust, forms in rocks.

When these mineral particles are hit with a laser beam, quantifiable helium gas is released.

“In a very simplistic sense, the amount of helium in the mineral is kind of a clock,” says Max.

“We can calculate the age of mineral formation and relate this to the climate response.”

species division

As the Nullarbor dried out, it formed a vast biogeographic barrier. This forced the species to migrate to more favorable habitats east and west.

According to Max, this is probably why many species with a common ancestor evolved separately on opposite sides of the country.

“My favorite example is the black cockatoo,” he says.

“In southeastern Australia you can find yellow-cheeked parrots. In southwestern Australia you’ll find white-cheeked Carnaby parrots.”

Another such example is the evolution of the bobtail lizard.

Defining this evolutionary timeline helps biologists understand how past climate change impacted biodiversity.

Clues to future climate

Beyond looking back at how past droughts have affected ecosystems, this knowledge may be useful in the future.

“It can inform our strategies regarding how species can adapt to that change,” says Max.

Studying drought phenomena like the Nullarbor is important because droughts are becoming more and more common.

Drylands (including arid, semi-arid and dry subhumid areas) cover almost half of the earth’s surface.

Australia is the world’s driest continent, with 70% of its land classified as arid or semi-arid.

“Roughly three billion people live in drylands today, and that number will increase,” says Max.

Over the past few decades, the intensity and extent of some of these drylands have increased.

Understanding past drying phenomena can help prepare for a warmer and drier future.

“We are contributing to the development of efforts to better protect ecosystems in the face of this kind of climate challenge,” says Max.

This article originally appeared on Particle. Please read the original article.

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