The earth, like so many of its human inhabitants, may have experienced a middle crisis that culminated in baldness. But it was not a diminishing hairline that our planet had to worry about; it was a descending skyline.
During nearly a billion years during the planet’s “middle years” (1.8 billion to 0.8 billion years ago), Earth‘s mountains have literally stopped growing, while erosion has weakened existing peaks to stumps, according to a study published in the journal on February 11. Science.
This extreme mountain-forming disruption – due to a persistent thinning of the Earth’s continental crust – coincided with a particularly gloomy eon that the geologist called the “boring billion, “the researchers wrote. Just as the Earth’s mountains could not grow, the simple life forms in the Earth’s oceans have not evolved (or at least been incredibly slow) for a billion years.
Related: Why do mountains not grow forever?
According to lead author Ming Tang, the mountain of trouble on the continents of the earth was possibly partly responsible for the slow course in the earth’s seas.
“In the Middle Ages, continents were mountainous,” Tang, an assistant professor at Peking University in Beijing, China, told WordsSideKick in an email. ” The flatter continents can reduce nutrients [to the ocean] and impedes the emergence of a complex life. ‘
When mountains disappear
At the confluent borders where Earth continental plate botsmountains soar upward in a process called orogeny. The continental crust at these boundaries is on average thicker and is driven by magma, raising the surface rocks to dizzying heights. Meanwhile erosion and gravity push back against the peaks; when the tectonic and magmatic processes stop below the surface, erosion is getting the mountains away.
Because even the most powerful mountains disappear over time, studying the earth’s crust thickness of the ancient earth may be the best way to determine how actively mountains have formed in the past. To do this, the authors of the study analyzed the changing composition of zirconminerals that crystallized in the crust billions of years ago.
Today, small circular grains are easily found in sedimentary rocks across the planet. The exact elemental composition of each grain can show the conditions in the crust where the minerals first crystallized.
“Thicker crust forms higher mountains,” Tang said. The thickness of the crust controls the pressure with which magma changes the composition, which is then recorded by deviations in zircons crystallizing from the magma, he added.
In a previous study published in the journal in January Geology, Tang and colleagues found that the amount of europium embedded in zircon crystals may reveal the thickness of the crust at the moment the crystals formed. More europium means a higher pressure placed on the crystal, which means a thicker crust above, the researchers found.
In their new study in Science, the researchers analyzed zircon crystals from each content and used the europium aberrations to construct a history of continental thickness dating back billions of years. They found that ‘the average thickness of active continental crust varies on billion-year-old time scales’, the researchers wrote, with the thickest crust found in the Archaic eon (4 billion to 2.5 billion years ago) and the Phanerozoic (540 million years ago to the present).
Between those active mountain-forming periods, the crust thickness decreases through the Proterozoic eon (2.5 billion to 0.5 billion years ago) and reaches a low point during the Earth’s “middle years”.
The eon of nothing
It may not be coincidental that the earth’s flattest eon on land was also the “most boring” eon at sea, Tang said.
“It is widely acknowledged by our community that the evolution of life between 1.8 and 0.8 billion years ago was very slow,” Tang told WordsSideKick. “Although eukaryotes Originated 1.7 billion years ago, they rose to dominance only about 0.8 billion years ago. ‘
In contrast, Tang said the Cambrian explosion, which took place just 300 million years later, introduced almost all important animal groups we see today. For whatever reason, life slowly began to develop during the ‘boring billion’, and then began, just as the crust began to thicken.
What is the connection? If no new mountains formed during this period, then no new nutrients were brought from the bottom of the mantle to the earth’s surface. water cycle. As mountaineering stalled for a billion years, there was a ‘famine’ of phosphorus and other essential elements could have starved the Earth’s simple seaworthiness, limited their productivity and hampered their evolution, the team suggests.
Life and mountains finally flourished again when the supercontinent Nuna-Rodinia broke apart at the end of the Proterozoic eon. But before that time, this gigantic continent could have been so massive that it effectively changed the structure of the mantle below. plate tectonics during the “boring billion” and which led to an eon of the fall of the crust, the researchers write. But further research is needed to completely solve the mystery of the disappearing mountains of the earth.
Originally published on Live Science.