Fossilized shark teeth found along coastlines and riverbeds often display a distinct black coloration. This dark hue is a result of a complex geological process that transforms the tooth after it is shed. Understanding this process unveils a fascinating aspect of Earth’s natural history.
How Shark Teeth Turn Black
The black color of fossilized shark teeth is primarily a result of permineralization, the fossilization process. After a shark sheds a tooth, it typically sinks to the seafloor and is rapidly buried by layers of sediment. This swift burial helps protect the tooth from decomposition by preventing exposure to oxygen and bacteria. Over thousands to millions of years, pressure from accumulating sediment compacts the material around the tooth.
Water, rich with dissolved minerals, then seeps into the buried tooth. These minerals gradually fill the microscopic pores within the tooth’s structure, replacing original organic materials like dentin and enamel. The specific types of minerals present in the sediment dictate the fossil’s final color. Iron sulfides, manganese dioxide, and phosphates are common minerals that contribute to deep black or charcoal gray shades. For instance, teeth found in the Peace River formation in Florida are often black due to the high concentration of phosphate.
Black Teeth in Living Sharks
Living sharks do not have black teeth; their teeth are typically white or off-white, much like human teeth. These teeth are primarily composed of calcium phosphate, forming a hard mineral called apatite. The dark coloration seen in fossilized teeth is a post-mortem phenomenon, occurring long after the tooth has been shed.
The transformation to a dark color occurs exclusively through interaction with minerals in the earth, not within a living shark’s mouth. Therefore, shark jaws displayed in museums feature white teeth, reflecting their natural state. The absence of white shark teeth on beaches is because unfossilized teeth usually disintegrate over time if not buried and preserved.
Other Colors of Fossil Shark Teeth
While black is a prevalent color for fossilized shark teeth, these ancient remnants can exhibit a diverse palette. The color variations are directly linked to the specific mineral composition of the sediment where the tooth fossilized. For example, iron oxides in the sediment can impart reddish or brownish hues.
Teeth found in clay-rich environments might display shades of gray or bluish tones. Conversely, burial in sediments rich in calcium carbonate, such as limestone, can result in lighter colors like white or light gray. Organic materials like tannins, often found in riverbeds, can also stain teeth dark brown. This range of colors provides clues about the geological environment and mineral content of the ancient locations where these teeth were preserved.