2023-11-28 07:07:47
490 million years ago, Thailand was part of Gondwana. But where exactly was this small piece positioned? The recent discovery of trilobite fossils helps answer this question, establishing the connections existing at the end of the Cambrian with other parts of this supercontinent.
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490 million years ago, the earth’s landscape was far from what we know today. We are then at the end of the Cambrian, a very critical period in the history of life on earth. The supercontinent Pannotia has completed its fragmentation, giving way to several lithospheric mega-plates named Laurentia, Baltica, Siberia and the largest: Gondwana.
Within the latter are grouped the lands which, hundreds of millions of years later, will form South America, Africa, Antarctica, Australia, Arabia, India and the continent recently mapped Zealandia. In the vast oceans that separate these four large continental masses, a multitude of small animals thrive. Among them, trilobites. These shelled arthropods diversified very quickly during the Cambrian and colonized all the oceans. They will eventually become extinct during the mass extinction which will mark the end of the Permian and the entry into the Mesozoic era, 251 million years ago. Today, trilobite fossils are certainly the most emblematic of the Paleozoic era. Fossils which are of major interest for reconstructing the evolution of the continents during this distant period.
Fossils connect the pieces of the great tectonic puzzle
The continents are in fact constantly moving, pushed by the continuous formation of the oceanic crust at the level of the ridges. Thus, these movements can be reconstructed thanks to the magnetic anomalies recorded gradually in the rocks of the oceanic crust. A method that works wonderfully, but only for the last 200 million years! Impossible to go beyond. And for good reason: the oceanic crust is continuously recycled at subduction zones. Currently, there is no oceanic magnetic anomaly on Earth older than 200 million years. To reconstruct the history of continents beyond this date, scientists must therefore find other tips. Fossils, and in particular trilobites with their formidable diversity, can in this context carry a lot of information.
Fossils that help reconstruct the puzzle of Gondwana
This is how the discovery of trilobite fossils made it possible to correctly place the location of Thailand in the great tectonic puzzle that represents Gondwana. The fossils were found on the Thai island of Ko Tarutao, within a layer of ash that was originally deposited on the ocean floor during a volcanic eruption. However, volcanic ash contains zircons, small, very resistant minerals whose radioisotope analysis made it possible to date the eruption, and the fossils at the same time.
The trilobites would therefore be around 490 million years old (end of the Cambrian). The species identified are new to Thailand, but have already been found in other regions of the world, notably Australia and northern and southern China. This new paleontological discovery, published in the magazine Palaeontology, thus makes it possible to connect several pieces of the tectonic puzzle of Gondwana. A connection with the continent Laurentia (present-day North America), where certain undated specimens have been found, also seems possible.
490 million years ago, this region of Thailand was part of the outer margin of the supercontinent Gondwana. The trilobite fossils discovered therefore help to draw a more precise map of terrestrial geography at the end of the Cambrian.
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