|The chemical element europium present in the crystals of the mineral zircon has been the key for scientists to study the history of the Earth’s topography|
An international team – including researchers from Peking University, University of Toronto, Rutgers University and the University of Science and Technology of China – found evidence that suggests the Earth was mostly flat during its middle ages. In their paper published in the journal Science, the group describes their study of europium embedded in zircon crystals and what it revealed about Earth’s ancient past.
The report – published on the Phys.org website – indicates that previous research found that approximately 1.8 to 0.8 billion years ago, the Earth went through a quiet period when the evolution of life slowed dramatically, which the researchers attribute in their new study To a slow tectonic activity, which led to the absence of mountains at that time.
Previous studies also stated that the amount of europium present in the zircon crystals can be used to reveal the thickness of the earth’s crust at the time of crystal formation. The more europium is in the crystal, the more pressure is applied to it from above, indicating a thicker crust.
Thus, previous studies gave researchers the key to solving the mystery, so the researchers studied samples of zircon crystals that were collected from multiple places around the world.
To track the emergence of mountains throughout Earth’s history, the researchers relied on studying an anomaly of europium incorporated into the shattered zircon crystals.
|During the middle period of Earth’s life, the Earth’s crust was thinner than it is now|
The researchers found that the average thickness of the active continental crust varied over a time scale of up to one billion years, and that the thick crust had been formed in the Archaean Era, or the so-called Paleozoic, which is the second geological eras that spanned from 4 thousand to 2500 million years ago, and in the Phanerozoic, encompassing roughly 600 million years of the last Earth’s life.
In contrast, the Proterozoic Era, which began about 2,500 billion years ago and lasted until 542 million years, has seen a steady decline in the thickness of the Earth’s crust, leaving the continents devoid of high mountains until its end.
Mountains and refreshing life
The team found evidence indicating that during the middle period of Earth’s life, the crust was thinner than it is now, to the point that there were no mountains at all. Instead, the planet was covered with oceans and flat land masses. Conditions like these indicate that tectonic activity must have slowed down dramatically or stopped completely for nearly a billion years.
The researchers also noted that the tectonic activity that pushes mountains towards the sky and the subsequent erosion processes would have enriched life in the oceans, due to the primary role of mountain belts in hydrological processes, and thus in the nutrient cycle, which makes the evolution of life possible on the surface of the earth.
|The formation of the supercontinent Nuna-Rodina may have caused tectonic activity to stop|
Thus, with the absence of such cycles, evolution has slowed dramatically, which was shown by previous research that studied the middle period of Earth’s age, without explaining the reason behind this.
The researchers were unable to explain why the tectonic activity stopped, or why it lasted for a long time, but they indicated that it may be due to the formation of the supercontinent Nuna-Rodina, which changed the thermal structure in the Earth’s mantle layer and weakened the continental lithosphere.
This calm, caused by the prolonged cessation of tectonic activity, may have led to continuous famine in the oceans and halted the development of medieval life in the age of the Earth.
- Orogenic quiescence in Earth’s middle age: https://science.sciencemag.org/content/371/6530/728