183-million-year-old “golden” fossil fooled scientists for decades: Microscope reveals a completely different truth
A fossil that appears to shine like gold has been quietly misleading scientists for decades. Found in black shale deposits in southwest Germany, these 183-million-year-old remains, mostly ammonites, were long considered classic examples of pyritisation. In simple terms, researchers believed the original biological material had been replaced by pyrite, a mineral often called fool’s gold because of its metallic shine. The idea seemed logical and widely accepted.According to CPG, new analysis has started to challenge that assumption. Using advanced microscopy, scientists have taken a closer look at these fossils and found something unexpected. The golden appearance is not coming from where experts once thought.
Inside the 183-million-year-old fossil
For years, the internal structure of these fossils was assumed to be rich in pyrite. That belief shaped how researchers understood their preservation. The metallic look reinforced the idea, and few questioned it in detail.When scientists examined the fossils under a scanning electron microscope, the results told a different story. They found almost no pyrite within the fossil material. In some samples, only a handful of tiny crystals were present.Instead, the fossils appear to be made largely of phosphate minerals. This process, known as phosphatisation, happens when organic material is preserved very early, before it fully breaks down. Experts say this type of preservation is relatively rare and can retain fine structural details that are often lost in other fossilisation processes.So the fossil itself is not metallic in composition, even though it looks that way.
What makes the 183-million-year-old fossil look like gold
The source of the golden glow seems to sit in the surrounding rock rather than inside the fossil. The black shale that encases these remains contains large numbers of microscopic pyrite structures called framboids.These tiny formations are clustered and reflective. When light hits them, it scatters in a way that creates a metallic sheen. To the human eye, the effect looks as though the fossil itself is shining. Researchers counted hundreds of these framboids in the rock around a single specimen. Inside the fossil, there were only a few.That contrast suggests the golden effect is largely visual.
Low oxygen and brief oxygen pulses preserved the fossil
These fossils originated from the Toarcian Oceanic Anoxic Event, an era that existed some 183 million years ago when most areas in the ocean experienced extremely low oxygen concentrations. Oxygen deficiency could possibly cause slower rates of decomposition, hence the high-quality preservation of fossils from the area.However, it may not be the only factor at play. From the research, it appears that there was a brief interval where oxygen concentration in the water was higher. This may have caused chemical reactions resulting in phosphates replacing the biological materials before decomposition took place.While oxygen is generally associated with fast rates of decomposition, oxygen deficiency could play a critical role in preserving fossils. According to the researchers, it may be crucial to the fossilisation process.
What this fossil reveals about Earth’s past and future
The distinction may appear to be insignificant at first; however, it alters the perception of one of the most extensively investigated fossil sites in the world. The Posidonia Shale has long served as a reference in paleontology research. Any misinterpretation of this site’s conditions of preservation could impact the analysis of analogous samples worldwide.A contemporary relevance of these fossils becomes obvious if the decrease in the ocean’s oxygen content is considered. According to recent data, global oceanic oxygen concentrations fell by two per cent from the mid-20th century onwards.By analysing how this factor changed in the past, researchers can predict future developments more accurately.
