Travelling back into the Earth's past

Libraries from the early days of the planet

In addition to traces of simple life forms, the drill cores also contain numerous other pieces of information. This allows the scientists to draw conclusions about the lunar orbit and to analyse the tides, volcanism, UV radiation, the intensity of weathering, meteorite impacts and the temperature of the oceans and the atmosphere. The decoratively patterned stone cylinders are veritable libraries from the early days of our planet.

The species Orobates pabsti was named after Wilhelm Pabst, who was the curator at the Ducal Museum in Gotha. He was one of the first people to discover and describe »track slabs« at the turn of the 20th century. These are slabs of rock on which the footprints of primeval animals are preserved. Later, individual bones and even entire skeletons came to light. The most well-known are arguably the »Tambach Lovers«, a pair of Seymouria sanjuanensis immortalized side-by-side in stone for millions of years. Dr Thomas Martens, a geologist and palaeontologist, was the first to discover fossils at the Bromacker site in 1974. The student of Arno Hermann Müller has made studying the Bromacker fossils his life's work. He has even bought the site to secure it for science.

As soon as the drill cores are extracted from rock, they are measured and precisely labelled. By cataloguing and securely archiving them in this way, they are made available for further investigations, including future generations of researchers. This principle applies to both the drilling project in South Africa and the work in Thuringia. Over the course of the drilling project in the Barberton Greenstone Belt, the diamond core bit drilled down to a depth of 300 metres – often from older to younger layers of rock – at an angle of 45 degrees. »Around 20 to 40 metres of cores were extracted every day,« says Christoph Heubeck. In Thuringia, the drilling depth increased by eight metres every day until around 250 metres depth had been reached.

The drilling itself was essentially routine work. The geologists had originally identified a spa hotel's car park as the most promising drilling site. As the hotel did not close in the winter, however, another site had to be found. »We ended up drilling in the forest, right next to a forest road,« recalls Christoph Heubeck. The only sour note for the contracted company came when the drill bit broke off at a depth of 243 metres and had to be replaced.

A large core drilling rig was the main exploratory tool used in both projects. »In terms of approach, this is not much more than a magnifying glass or a hammer,« says Christoph Heubeck. »It's not so much the size and type of equipment that matters, but a smart choice of research question, the best possible location for carrying out the work, efficient data acquisition and optimal evaluation«.

As the sedimentary rocks that provide information about the Earth's geological past are usually covered by younger layers, weathered soils and vegetation, core drilling is often the method of choice for extracting unweathered and continuous material, which can then be »interrogated« in the laboratory.

This opinion is clearly shared by those involved in the International Continental Scientific Drilling Program (ICDP), the main funder of the South African project. That's why a major conference on the future of scientific drilling will be held in Potsdam in July 2023.

The first insights emerge even as the drill cores are being cut open. On first inspection, Christoph Heubeck points at blue-grey lumps in the drill core: »Those are carbonate nodules. Their isotopes act as a paleothermometer«. This means that the researchers can use these lumps to analyse what the temperature was like when the mineral formed. In this way, statements can be made about the climatic conditions of prehistoric times and comparisons can be made with today's conditions.

The scientific evaluation of the drill cores will not take anywhere near as much time. Nevertheless, it will take a few years before these time capsules from the early days of Earth will have been comprehensively examined and analysed, says Christoph Heubeck. Firstly, they are sawn lengthwise, photographed and described. Then one half was trucked to South Africa's national core repository, effectively a »library of the underground«; the other half has been shipped to the ICDP's core repository in Berlin-Spandau, where they are currently X-rayed, documented again in detail and distributed to the participating research institutions during a sampling workshop.

The area around the Bromacker site once resembled the landscape of today's Mongolia, as noted on one of the information boards. Anna Pint explains that it was a sedimentary basin; the sandstone was laid down in rivers that crossed the area. The aim now is to create an exact scientific reconstruction of the habitat found in this distant period. »We're looking through a window into the past and exploring a section of the Earth's history,« says Anna Pint. By »we« she means Christoph Heubeck and his team: Thomas Voigt, Frank Linde, Peter Frenzel and Anna Pint, as well as the students Jakob Stubenrauch, Rebecca Lellau and Fabio Berlin. The group from the University of Jena is the smallest in the Bromacker project, which was launched in 2020 and is scheduled to run for five years.