SBMA Science Series: The Meg Was Here!
Welcome to the latest instalment in our series of science articles brought to you by the Seabed Minerals Authority. We aim to educate and empower our readers by exploring the fundamental science related to deep ocean seabed minerals. Through these articles, we hope to shed light on the mysteries of the deep sea and its incredible resources, highlighting sustainable and responsible exploration. Join us on this journey to the depths of the ocean, where every discovery brings us closer to understanding our planet and protecting its future. Please check out our website for all our science articles released so far.
Introduction
When you think of the deep ocean, you might imagine mysterious creatures, sunken ships, and lost treasures. However, the reality is a bit more surprising—and a lot more cluttered. Shoes, plastic bags, glass bottles, fishing gear, and even entire shipping containers can be found scattered across the ocean floor. One particularly eye-opening discovery was a beer bottle found in the Challenger Deep, the deepest part of the ocean, over 10,000 meters down [1].
But the deep sea isn't just a dumping ground for human trash. It's a dynamic and fascinating ecosystem filled with life, from gigantic whales to tiny microorganisms. When these organisms die, their remains sink to the ocean floor, providing food for other sea creatures and contributing to the formation of various minerals.
Life and Death on the Ocean Floor
Many sea creatures have shells made of calcium carbonate. When they die, these shells sink and eventually turn into limestone, especially around the volcanic flanks of islands [2]. However, at great depths, where polymetallic nodules form, you won't find this limestone. This is because calcium carbonate dissolves in cold, high-pressure environments below a certain depth known as the carbonate compensation depth (CCD). In the Cook Islands, the CCD is around 4,000-5,000 meters deep [3].
Fossils on the Ocean Floor
Interestingly, not all parts of ocean creatures dissolve. Teeth, made of calcium phosphate, remain intact even at great depths. Scientists have found ancient teeth on the ocean floor, some of them belonging to the megalodon, an extinct giant shark [4]. A few have been recovered during expeditions studying the polymetallic nodules in the Cook Island region. Imagine a shark tooth as big as your hand, recovered from the seabed! These teeth are remnants of a creature that lived about 23 million years ago and went extinct around 3 million years ago.
Understanding the Megalodon
Megalodons were massive predators, possibly up to 20 meters long and weighing over 100 tonnes—bigger than a bus! Their teeth were thick and strong, perfect for attacking and eating large marine animals. Just like modern sharks, megalodons lost their teeth frequently, which is why we find so many of them today.
The megalodon first appeared about 23 million years ago. They became extinct about three million years ago, coinciding with the ice ages that cooled the oceans and lowered the sea level, changes that may have made it difficult for the megalodon to live and breed.
Public-domain drawing of megalodon - Graphic depicting megalodon size
Dating Ancient Fossils
Sharks tooth recovered during exploration expedition in the Cook Islands. Believed to be a megalodon shark tooth.
We know when megalodon appeared and went extinct by studying their fossils [5]. Fossils were little more than curiosities until the seventeenth century when scientists systematically studied and classified them and began to understand how the plants and animals they represented were related, even over long distances.
This knowledge enabled fossils to become the primary tool for mapping the ages of rocks around the world. The real breakthrough came when isotopic techniques were used to establish absolute ages for fossils. This involves analysing the amounts of certain elements that decay at known rates[6].
While no one has yet dated a megalodon tooth from the Cook Islands, the shape and size of the teeth can be compared to other dated specimens to estimate their age.
A Glimpse into the Past and Future
The megalodon tooth in our picture has turned black due to the deposition of ferro-manganese minerals, the same process that forms polymetallic nodules. You may remember from a previous article that these nodules grow very slowly, about a centimetre per million years. This tells us that the tooth has been lying on the ocean floor for a very long time. In a million years or so I wonder what future explorers will think of all our rubbish, like a shoe, lying on the seafloor covered in ferro-manganese minerals? It’s a humbling thought and a reminder of our impact on the planet.
Conclusion
The deep ocean is a fascinating and complex world. It's not just a resting place for our discarded items but a rich environment that holds the keys to our planet's history. By studying the deep sea, we can learn more about Earth's past and how to protect its future.
References
Greenaway, S. F., Sullivan, K. D., Umfress, S. H., Beittel, A. B., & Wagner, K. D. (2021). Revised depth of the Challenger Deep from submersible transects; including a general method for precise, pressure-derived depths in the ocean. Deep Sea Research Part I: Oceanographic Research Papers, 178, 103644. https://doi.org/10.1016/j.dsr.2021.103644
’Steven, S. (2005). Earth System History (1st ed.). W. H. Freeman.
Emerson, S., & Hedges, J. (2008). Chemical Oceanography and the Marine Carbon Cycle. Cambridge University Press. https://doi.org/10.1017/CBO9780511793202
Pimiento, C., & Balk, M. A. (2015). Body-size trends of the extinct giant shark Carcharocles megalodon : a deep-time perspective on marine apex predators. Paleobiology, 41(3), 479–490. https://doi.org/10.1017/pab.2015.16
Pimiento, C., & Clements, C. F. (2014). When Did Carcharocles megalodon Become Extinct? A New Analysis of the Fossil Record. PLoS ONE, 9(10), e111086. https://doi.org/10.1371/journal.pone.0111086
Bronk Ramsey , C. B. ( 2008 ). Radiocarbon dating: revolutions in understanding . Archaeometry , 50 ( 2 ), 249 – 75.