South Australia Naracoorte CavesOne of the most important fossil sites in the world, with a record that spans more than half a mile.
The bones of iconic Australian megafauna species are among the remains that have been preserved in layers of sand. ExtinctBetween 48,000 to 37,000 years ago.
It is still not clear what caused the extinction of megafauna. However, the more fossils that we find the older we are able to understand the evolution and eventual extinction of the species.
It has been hard to determine the exact age of the caves. However our research demonstrates, for the first time, how old Naracoorte’s caves really are – and the answer is up to 500,000 years older than previously thought.
Our research sheds new light on the importance of this place’s antiquity. We hope that this will allow us to better understand how biodiversity responds over time to climate change.
A moment in geologic history
Caves can be amazing time capsules. They often preserve the remains of extinct animals and plants in incredible detail. One example is the Naracoorte Caves, South Australia.
This cave complex is South Australia’s only World Heritage Site. The fossils of megafauna, such as:
- Thylacoleo carnifex (marsupial predator)
- Zygomaturus trilobus (huge herbivore)
- Wonambi naracoortensis(giant constrictor serpent)
- Procoptodon goliah (browsing sthenurine kangaroo).
Paleontologists have dated and excavated many fossil deposits, and also reconstructed the bones of several megafauna species.
Caves were formed by groundwater leaking through cracks in limestone rocks. This dissolution caused them to dissolve and created cavities. They were previously dated between Between 0.8 million and 1.1million years old – an estimate generated by dating a fossil dune ridge that lies over the cave complex.
The methods used to date a ridge in the sand dunes were however not available. Not CompletelyIt was the right material for the job. So far, no age has been determined for the caves.
The complex work required to conduct our study took us five years. But it was worth it.
What we did
The dating method We usedIt was fascinating to see the beautiful calcite formations within the caves. These are collectively known as’speleothems’. They include stalagmites and stalactites, as well as flowstones.
When speleothems form, tiny amounts of uranium – a radioactive element – are locked inside them.
Over time, uranium gradually decays into the element led. This occurs at a known, constant rate – which means we can use uranium in speleothems as a natural clock to date them.
This involved extracting uranium from the speleothem and putting it in a laboratory. Each element was measured and the age calculated very accurately.
Speleothems can only begin to grow when a subterranean cave is created and above groundwater table. The oldest speleothem age indicates the minimum age of the cave.
From this, we found the caves began to form at least 1.34 million years ago – making them 250,000 to 500,000 years older than previous estimates.
Our second study focused on the opening of caves to allow air and animals to enter.
This was done by looking at microscopic pieces of charcoal and pollen that were captured in the calcite formations during their growth.
Around 600,000 years ago, charcoal and pollen were first discovered in caves. This suggests the caves may harbor exciting new vertebrate fossil material up to 600,000 years old – more than 100,000 years older than the oldest known fossil depositsThe complex.
This is why it matters
It’s hot DebateAbout whether the extinction Australia’s megafaunaThe climate or humans caused it.
To understand when and how fast natural processes took place over time, a good chronology is crucial. We cannot determine the rate at which landscapes, climate, and biodiversity are changing without precise ages.
So, while the Naracoorte Caves were formed approximately 1.34million years ago, the caves did not reach the surface until 600,000.
This brings out the enormity of time separation between fossil accumulation and landforms evolving.
Our findings will also help paleontologists target new excavation sites to find older fossils – hopefully providing valuable further evidence of how our continent’s unique biodiversity has changed.
Our new approach will help uncover the secrets of old fossil deposits in other cave complexes. Australia AroundThe WorldWhere both vertebrate and speleothem fossils can be found.
The future of Australia’s diversity in animal and plant species could be uncertain. Climate changeOther human impacts
Important sites like the Naracoorte Caves help us to understand how climate change has influenced biodiversity in the past and what may happen in the future.
Rieneke Weij, Postdoctoral researcher in Geochemistry/Palaeoclimatology, University of Cape Town; Jon WoodheadResearch Scientist Kale SnidermanSenior Research Fellow The University of Melbourne?, and Liz ReedResearch Fellow University of Adelaide
This article was republished by The ConversationUse the Creative Commons license Please read the Original article.
