Limestone and iron reveal Western Australia’s mysterious extreme rains 100,000 years ago

Almost one-sixth of the Earth’s surface is covered in otherworldly landscapes with an unfamiliar name: karst. These landscapes are like natural sculpture parks, with dramatic formations dotted with caves and rock towers slowly carved by water over thousands of years.

Karst landforms are beautiful and ecologically important. They also represent a record of Earth’s past temperature and humidity levels.

However, it is very difficult to know exactly when karst landforms were formed. A new study published today in Science Advances shows a new way to find the age of these mysterious landscapes, which could help us understand Earth’s past in more detail.

challenge

Karst is defined by the removal of material. The rock towers and caves we see today are what remained after water dissolved the remains during past rainy seasons.

This is what makes it difficult to determine their age. How do you find out the date something went missing?

Traditionally, scientists have roughly classified the age of karst surfaces by measuring the age of the material above and below the surface. However, this approach obscures our understanding of ancient climate phenomena and how ecosystems responded.

geological clock

In our research, we discovered a way to measure the age of pebble-sized iron blocks that formed at the same time as karst formations.

This method has the technical name (U/Th)-He geochronology. This study will measure how much helium is produced by the spontaneous radioactive decay of trace elements uranium and thorium in iron nodules. By comparing the amounts of uranium, thorium and helium in the sample, the age of the nodule can be calculated with great accuracy.

We dated microscopic fragments of iron-rich nodules from the iconic Pinnacles Desert in Nambun National Park, Western Australia.

This world-famous site is famous for its otherworldly karst formations, with limestone pillars towering meters above the sandy desert plains. The Pinnacles form part of the world’s most extensive belt of wind-blown carbonate rocks, stretching more than 1,000 km along the coast of southwestern Washington state.

We examined multiple microscopic iron nugget fragments removed from the surface of a limestone spire. These masses were formed in the soil overlying the limestone during periods of intense weathering that formed karst. As a result, they serve as time capsules of the environmental conditions that shaped the area.

big wet

We have consistently found that the growth age of iron nodules is approximately 100,000 years. This age is supported by known ages obtained from rocks above and below the karst surface, proving the reliability of our new approach.

As chemical reactions caused iron-rich nodules to grow within the ancient soil, the limestone bedrock rapidly and extensively dissolved, leaving only the limestone spiers seen today.

Examination of the entire rock sequence in the region suggests that this period of intensive weathering was the wettest period in this part of Washington state in at least the past 500,000 years.

We don’t know what caused this increase in rainfall. It could be a change in atmospheric circulation patterns or a major influence of the ancient Leeuwin Current flowing along the coast.

These wet periods contrast dramatically with recent droughts and the region’s increasingly dry climate today.

Influence on our past

Iron-rich nodules are not unique to Nanbun Pinnacles. These have recently been used elsewhere in Australia to track dramatic environmental changes in the past.

Determining the age of these iron nuggets will help better document the dramatic changes in Earth’s climate over the past three million years as ice sheets grow and shrink.

Understanding the timing and environmental conditions of karst formation during this period provides deep insight into past climatic conditions, environments, and landscapes inhabited by ancient organisms.

Climate change and the accompanying environmental changes are extremely important in shaping ecosystems. In particular, they have had a profound influence on ancient humans and our ancestors.

By linking karst formation to specific climatic intervals, we can better understand how these environmental changes affected early human populations.

I’m looking forward to it

The more we learn about the conditions that led to the formation of past landscapes and the plants and animals that lived there, the better we can understand the evolutionary pressures that shaped the ecosystems we see today. This provides valuable information to prepare for future changes.

As human-induced climate change accelerates, learning about past climate change and biosphere responses provides knowledge to predict and mitigate future impacts.

Being able to date karst landforms more precisely may seem like a small thing, but it has implications for understanding how current landscapes and ecosystems will respond to current and future climate change. Helpful.

This article is republished from The Conversation under a Creative Commons license. Read the original article.