The black shark tooth represents the fossilized remains of ancient marine predators, often from the Cenozoic Era. These durable specimens, found globally, were shed by species like the colossal Carcharocles megalodon and various extinct relatives of modern sharks. Determining the specific age of these teeth requires understanding the geological processes that preserved them and the context of their discovery.
The Fossilization Process and Color
The dark color of these fossils is often mistaken as an indicator of great age, but it results from the chemical process of fossilization. When a shark loses a tooth, it sinks to the seafloor and must be rapidly buried by sediment to prevent decay by oxygen and bacteria. This burial initiates permineralization, the process where the original organic material of the tooth is replaced by minerals from the surrounding environment.
The black coloration occurs when the sediment is rich in elements like manganese, iron, or phosphate. Water carrying these dissolved minerals seeps into the microscopic pores of the tooth’s crystalline structure, replacing the original calcium phosphate. For instance, the presence of manganese often yields a dark gray to black hue. Therefore, the color reflects the specific geochemical environment of the burial site, not the number of millions of years the tooth has existed.
Dating Through Geologic Context
To determine how old a fossil shark tooth is, paleontologists rely primarily on relative dating methods, focusing on the age of the sedimentary rock layers where the specimen was found. This methodology is centered on stratigraphy, which applies the principle of superposition, stating that in an undisturbed sequence of rock layers, the oldest strata are at the bottom. By identifying the exact layer where the tooth was embedded, scientists can bracket its age relative to the surrounding rock.
Shark teeth alone are generally poor indicators of precise geologic time because many shark species evolved slowly and persisted for millions of years. Instead, researchers look for index fossils within the same layer of sediment. Index fossils are the remains of organisms that lived for a relatively short period but were geographically widespread, such as specific species of foraminifera or mollusks. The known age range of these associated index species provides a narrower temporal window for the shark tooth.
Absolute Dating Methods
Absolute dating techniques, such as Carbon-14 dating, are generally not applicable because the teeth are far too old to contain measurable amounts. However, volcanic ash layers found directly above or below the fossil-bearing strata can be dated using radiometric methods like Argon-Argon dating. Additionally, the strontium in the tooth’s enameloid can be analyzed using Strontium Isotope Stratigraphy, comparing its isotopic ratio to the known global seawater strontium curve to yield a numerical age estimate.
Establishing Specific Geological Ages
The vast majority of black shark teeth found by collectors originate from the Cenozoic Era, which spans the last 66 million years. The most abundant finds are concentrated in the Miocene and Pliocene epochs, roughly between 23 million and 2.6 million years ago. This period aligns with the peak diversification and eventual extinction of many large shark species.
The most sought-after black shark teeth often belong to the extinct giant, Carcharocles megalodon, which existed from the late Oligocene through the Pliocene (approximately 28 million to 2.6 million years ago). Identifying a tooth based on its size, thickness, and serrations immediately places it within this multi-million-year range. Other common teeth might be from early ancestors of the modern Great White Shark or various extinct mackerel sharks, placing them in similar or sometimes older Cenozoic periods, such as the Eocene.
The specific age of a find varies significantly based on the region where the teeth were deposited and the geological formation they weathered out of. For example, teeth found in the Hawthorne Formation of the southeastern United States are often Miocene to Pliocene in age. Some black teeth found in coastal areas may be much older, occasionally dating back to the Cretaceous Period, which ended 66 million years ago. Therefore, their age is ultimately determined not by their color, but by correlating species identification with the established geologic age of the sediment layer where they lay buried.