Prehistoric Kauri trees and the Earth's climate

The ancient Kauri trees provide interesting clues about the earth's climate in the past, today and in the future.

This 38,000-year-old kauri trunk, which has enormous scientific value, was used for this purpose. Such a large, ancient tree specimen with its annual rings provides invaluable information for research groups specializing in analysis.

This tree would help us to better understand an ancient global catastrophe and its consequences for the Earth's history.

‍

Growth rings from the Kauri tree as a source of information

As they grew, they stored information about the climate and the composition of the atmosphere in their annual rings. After they fell over, the trees sank deep into the peat bog, where they remained buried almost unchanged for thousands of years.

Tree rings shed light on the past in various ways. If you count them, you first find out how long a tree has lived. The width of the individual annual rings in turn allows conclusions to be drawn about changing growth conditions. A chemical analysis of each ring provides information on precipitation patterns, relative humidity and soil moisture.

Millennia-old "climate records" in the Kauri

Using computer programs and a visual examination of tree ring patterns, samples from different times and places can be combined into long sequences, so-called chronologies. In some cases, these extend seamlessly over thousands of years and reveal supra-regional patterns in climate events. For comparison: historical climate records only go back 150 years.  

The timeline going further back in time now provides climate modelers with important data to predict the development of the climate in the future, for example in the context of man-made global warming. Researchers have created a number of other kauri chronologies that go back even further into the past. Each of them spans several millennia over the past 60,000 years.

Prehistoric kauri samples are invaluable for science worldwide. For example, researchers can use them to classify the age of other plant, human and animal finds that have survived for tens of thousands of years. 

Using the radiocarbon method, the age of the kauri tree was estimated at 38,000 years.

Sea rise of 15 meters

A new finding is that the sea level rose by more than 15 meters 15,000 years ago due to melting ice sheets. And this happened much faster than previously assumed, as the new curves show: The process was over after just 160 years. This shows that Sea levels can also rise very suddenly, not just gradually as a result of rising global temperatures - a potentially important lesson in times of melting Antarctic ice sheets.

Changes in the magnetic field

Apart from that, the Kauri annual rings provide information about changes in the Earth's magnetic field, such as those that occurred in 1859. At that time there was a solar flare, a huge coronal mass ejection that bombarded the Earth with radiation. This resulted in a one-day geomagnetic storm, the Carrington Event. 

‍

Solar storms are not the only geomagnetic events immortalized in kauri wood. Around 42,000 years ago, the Earth's magnetic field began to wander for a millennium and briefly reversed its polarity in a pole excursion. When scientists adjusted the tree's radiocarbon dates using the calibration curve, it became clear that they covered the beginning of this event. The kauri had grown into a sapling around 42,715 years ago and collapsed into the mud 1600 years later.

The information in the tree's rings was compared with other natural archives to create a precise sequence of events. According to this, when the Kauri tree was a few hundred years old, the Earth's magnetic field weakened dramatically. At the same time, the sun entered a periodic, century-long dormant phase with far fewer sunspots and lower energy output, a so-called grand solar minimum.

During this phase, the solar wind and the solar magnetic field weakened, serving as a protective shield for the Earth against cosmic radiation. As a result, the Earth's atmosphere was poorly protected for several hundred years.

‍

Beginning of the ice age

In the following few centuries, the ice sheets in North America grew rapidly, while the climate in Australia became drier and the lakes in the interior disappeared. Incidentally, these changes took place more than 10,000 years after the arrival of modern humans on the continent.

According to the study, humans are not responsible for the disappearance of animal and plant species at that time. This explains a series of patterns around 42,000 years ago that were previously a mystery.

Climate influence by geomagnetic and solar events

Contrary to previous knowledge, severe geomagnetic and solar events could very well influence the global climate, the scientists continue. This perspective opens up a new multidisciplinary field of research. The planet and climate system are now much more variable. The key to all these new insights and perspectives came from excavated kauri trees. "To come across a phase with such a weak geomagnetic field is really unusual," say scientists who studied the tree, "and then to find such a long-lived tree that lived through exactly this period.