Fossil-Crammed Australian Caves Might Be 500,000 Years Older Than We Thought, Research Finds : ScienceAlert

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South Australia’s Naracoorte Caves is likely one of the world’s finest fossil websites, containing a document spanning greater than half 1,000,000 years.

Among the many stays preserved in layers of sand are the bones of many iconic Australian megafauna species that turned extinct between 48,000 and 37,000 years in the past.

The explanations for the demise of those megafauna species are intensely debated. However the older the fossils we are able to discover, the higher we are able to perceive the species’ evolution and extinction.

Up to now, figuring out the exact age of the caves has been troublesome. Nonetheless our analysis demonstrates, for the primary time, how outdated Naracoorte’s caves actually are – and the reply is as much as 500,000 years older than beforehand thought.

Our findings shed new gentle on the antiquity of this vital place. We hope this can support understanding of how biodiversity responds to a altering local weather over time.

A second in geologic time

Caves might be extraordinary time capsules, typically preserving the stays of lengthy extinct crops and animals in beautiful element. The Naracoorte Caves in South Australia is one such instance.

The cave advanced is South Australia’s solely World Heritage website. Among the many remarkably numerous and full fossil document are the stays of iconic megafauna corresponding to:

  • Thylacoleo carnifex (marsupial predator)
  • Zygomaturus trilobus (big herbivore)
  • Wonambi naracoortensis (large constrictor snake)
  • Procoptodon goliah (searching sthenurine kangaroo).

Paleontologists have excavated and dated many of those fossil deposits and reconstructed the skeletons of a lot of megafauna species.

Lead creator Rieneke Weij descending right into a cave at Naracoorte. (Liz Reed, Creator offered)

The caves shaped when groundwater percolated by way of cracks in limestone rocks, dissolving them and forming cavities. They have been beforehand dated at between 0.8 and 1.1 million years outdated – an estimate generated by relationship a fossil dune ridge that lies over the cave advanced.

However the strategies used up to now the dune ridge have been not totally appropriate for the duty. As such, a exact age of the caves had not been obtained, till now.

This intricate work concerned in our examine has taken 5 years, but it surely was well worth the wait.

What we did

The relationship technique we used concerned inspecting the attractive calcite formations contained in the caves. Collectively, these are known as ‘speleothems’ and so they embody stalagmites, stalactites and flowstones.

When speleothems kind, tiny quantities of uranium – a radioactive component – are locked inside them.

Over time, uranium slowly decays into the component lead. This happens at a identified, fixed charge – which implies we are able to use uranium in speleothems as a pure clock up to now them.

Doing so concerned extracting uranium and lead from the speleothem in a laboratory. We then measured every component and calculate the pattern’s age very exactly.

As a result of speleothems solely begin to develop as soon as a subterranean cavity is shaped and above the groundwater desk, the oldest speleothem age reveals the minimal age of the cave itself.

Inside Whale Bone Cave, one of the oldest caves at Naracoorte in South Australia.
Whale Bone Cave, one of many oldest caves at Naracoorte. (Steve Bourne, Creator offered)

From this, we discovered the caves started to kind at the very least 1.34 million years in the past – making them 250,000 to 500,000 years older than earlier estimates.

The second a part of our examine sought to find out when the caves first opened to the floor, permitting each air and animals in.

We did this by inspecting microscopic particles of charcoal and pollen captured within the calcite formations as they grew.

We discovered charcoal and pollen first appeared within the caves round 600,000 years in the past. This means the caves might harbor thrilling new vertebrate fossil materials as much as 600,000 years outdated – greater than 100,000 years older than the oldest identified fossil deposits on the advanced.

Why this issues

There’s heated debate about whether or not the extinction of Australia’s megafauna was the results of people or the local weather.

An excellent chronology is essential to understanding when and the way shortly pure processes occurred over time. With out exact ages, we can’t know the speed of change to landscapes, local weather, or biodiversity.

So whereas the Naracoorte Caves shaped at the very least 1.34 million years in the past, they didn’t open to the floor till 600,000 years in the past.

This sheds new gentle on the huge separation in time between landforms evolving and fossils accumulating.

Our findings will even assist paleontologists goal new excavation websites to search out older fossils – hopefully offering beneficial additional proof of how our continent’s distinctive biodiversity has modified.

Our new strategy may also help to unravel how outdated fossil deposits at different cave complexes in Australia and round the world the place each speleothems and vertebrate fossils are discovered.

Australia’s richness of plant and animal species faces an unsure future, on account of local weather change and different human impacts.

Learning vital websites such because the Naracoorte Caves helps us perceive not simply how local weather change influenced biodiversity up to now, however what would possibly occur in future.The Conversation

Rieneke Weij, Postdoctoral researcher in Geochemistry/Palaeoclimatology, College of Cape City; Jon Woodhead, Analysis Scientist; Kale Sniderman, Senior Analysis Fellow, The College of Melbourne, and Liz Reed, Analysis Fellow, College of Adelaide.

This text is republished from The Dialog below a Inventive Commons license. Learn the authentic article.

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