Welcome back, fellow radiation nerds! Today, we’re diving deep into the radioactivity of ancient dinosaur fossils!

My Sample

During my recent trip to US, I visited the Meteor Crater which was an absolute amazing experience. After the tour, I went to the souvenir shop where I spotted some Megalodon teeth. I heard before that sometimes they can be radioactive, so I quickly took out my Terra-P Geiger counter and I got very excited when my meter started showing increased levels of radiation. Of course, I couldn’t leave without taking one home, and here I am!

Gamma spectroscopy and the activity

I was curious to what isotope made the my tooth radioactive so I used my RAYSID gamma spectrometer, to create a gamma spectrum which revealed that the tooth contains natural uranium. While the activity isn’t particularly high compared to something like uranium ore, it is definitely detectable and reads just under 1000 CPM on my Ludlum Model 3 with a 44-9 probe at 1cm distance and around 0.5uSv/h on my RAYSID also at 1cm distance.

How does a fossil become radioactive?

During the process of fossilisation, organic material is being replaced with the surrounding minerals, and if those minerals are contain uranium, the fossil can absorb them and become radioactive over time.

This isn’t just limited to Megalodon teeth either—it can happen to all fossils. For example, at the Grants Mining Museum in New Mexico, there are several dinosaur fossils with significant radioactivity due to them being fossilised in a uranium-rich environment.

Speaking of the Grants Uranium Mining Museum, I highly recommend visiting it if you get a chance. There is a lot of fascinating information and exhibits in it and the underground tour was a truly unique experience. I used to be a guide in a Uranium mine and I found it particularly interesting to see how uranium mining techniques compared between America and Eastern Europe.

Radiometric dating of fossils and rocks

Thanks to the decay of radioactive isotopes, scientists can estimate the age of different fossils. This process is known as radiometric dating, and some of the most commonly used isotopes are:

Carbon 14 – Naturally occurs in all living organisms and has a half-life of 5730 years. When the organism dies, it stops the resupply of carbon which allows scientist to date samples up to 50 000 years old.

Potassium 40 – It has a half-life of 1.25 Billion years and just like Carbon 14, it naturally exists in all living organisms. Since the half-life of K-40 is much longer, it allows scientists to date samples that are million of years old.

Uranium 238 – This method is used for dating zircon crystals found in volcanic ash layers associated with fossils. Uranium isotopes decay to lead isotopes with a half-life of 4.47 billion years, making it ideal for dating ancient rocks.

A few final words

Exploring the radioactivity of my Megalodon fossilised tooth was a lot of fun and I have learned a lot!

I’m curious to hear, do you have any radioactive fossils in your collection or maybe you didn’t even know they can be radioactive and you will check them now? Let me know in the comments!


Thank you so much for reading this post, I hope you enjoyed it and learned something new! If yes, please make sure to subscribe to the email list so that you get notified when new posts are added. Also feel free to check out my Ko-Fi page where you can donate a nice cup of radioactive coffee and support my work financially.

and remember, stay active!


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