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+--- Thread: Research New model refutes theory on how continents formed + More groundwater in SW Europe (/thread-16304.html)
New model refutes theory on how continents formed + More groundwater in SW Europe - C C - Aug 6, 2024
New model refutes leading theory on how Earth’s continents formed
https://today.uic.edu/new-model-refutes-leading-theory-on-how-earths-continents-formed/
PRESS RELEASE: The formation of Earth’s continents billions of years ago set the stage for life to thrive. But scientists disagree over how those land masses formed and if it was through geological processes we still see today.
A recent paper from the University of Illinois Chicago’s David Hernández Uribe in Nature Geoscience adds new information to that debate, poking holes in the leading theory of continent formation. Hernández Uribe used computer models to study the formation of magmas thought to hold clues to the origin of continents.
Magma is the molten substance that, when it cools, forms rocks and minerals. Hernández Uribe looked for magmas that match the compositional signature of rare mineral deposits called zircons that date back to the Archaean period of 2.5 to 4 billion years ago, when scientists believed that continents first formed.
Last year, scientists from China and Australia published a paper arguing that Archaean zircons could only be formed by subduction — when two tectonic plates collide underwater, pushing land mass to the surface. That process still happens today, causing earthquakes and volcanic eruptions and reshaping the coasts of continents.
But Hernández Uribe, assistant professor of earth and environmental sciences, found that subduction was not necessary to create Archaean zircons. Instead, he found that the minerals could form through high pressure and temperatures associated with the melting of the Earth’s thick primordial crust.
“Using my calculations and models, you can get the same signatures for zircons and even provide a better match through the partial melting of the bottom of the crust,” Hernández Uribe said. “So based on these results, we still do not have enough evidence to say which process formed the continents.”
The results also raise uncertainty about when plate tectonics started on Earth. If Earth’s first continents formed by subduction, that meant that continents started moving between 3.6 to 4 billion years ago — as little as 500 million years into the planet’s existence. But the alternative theory of melting crust forming the first continents means that subduction and tectonics could have started much later.
“Our planet is the only planet in the solar system that has active plate tectonics as we know it,” Hernández Uribe said. “And this relates to the origin of life, because how the first continents moved controlled the weather, it controlled the chemistry of the oceans, and all that is related to life.”
Groundwater reserves in southwestern Europe more stable overall than previously thought
https://www.ufz.de/index.php?en=36336&webc_pm=29/2024
PRESS RELEASE: “A widespread belief is that groundwater levels are continuously declining everywhere in southwestern Europe. However, a closer examination of the data reveals that the situation is more complex”, says UFZ hydrologist Dr. Seifeddine Jomaa, the corresponding author of the study. Data from 1960 to 2020 revealed that 68% of the examined wells showed stable levels over the past three decades, 20% of the wells showed rising groundwater levels, while only 12% showed a decline. “To avoid generalizations, a differentiated and detailed consideration of local groundwater systems is needed,” Seifeddine Jomaa says.
Stable groundwater levels are primarily located in temperate regions with year-round high precipitation, such as northern France. “In these regions, high recharge rates keep groundwater levels nearly stable," says Rafael Chávez García Silva, first author and also hydrologist at the UFZ. In other areas, like the lower Po River basin near Ravenna, groundwater levels are even rising due to natural and anthropogenic factors and land subsidence, requiring surface water drainage and groundwater pumping to prevent flooding.
In semi-arid regions, however, there are many places, such as Tarbes in France and Medina del Campo in Spain, where groundwater levels have been declining for decades. This is partly due to decreased rainfall and elevated temperatures brought about by climate change. Intensive agriculture is also a significant factor. “These four Mediterranean countries are responsible for a large part of the EU’s fruit, vegetable, and grain production, with groundwater supplying 30-50% of irrigation,” says Seifeddine Jomaa.
Even in temperate regions, the team found wells with declining groundwater levels. The cause is proximity to cities and industry. Since the 1960s, for example, groundwater levels in the metropolitan areas of cities such as Lyon, Nice, Modena, and Bordeaux have been declining. In Bordeaux, the ninth-largest city in France, the high groundwater consumption is attributed to increasing domestic use. The popular French tourist destination, Béziers, has seen a significant decline in groundwater levels due to increased extraction to supply drinking water for summer tourists.
While groundwater decline in urban and industrial areas is not easily halted, the researchers found effective management approaches in semi-arid, agricultural regions, which lead to the recovery of groundwater levels, as seen in La Mancha Oriental in Spain. Until the 1990s, groundwater levels were declining due to excessive irrigation. “As a result, sections of the Júcar River dried up in 1994 for the first time ever. This dramatic event prompted farmers to create a water user association that aimed to stop the decline in groundwater levels through a combination of monitoring, remote sensing, and individual water use plans. These measures effectively reversed groundwater level trends in the region,” says coauthor J. Jaime Gómez-Hernández, hydrogeologist at the Technical University of Valencia.
Against the backdrop of climate change, southwestern Europe can provide lessons for groundwater management in Germany and other regions worldwide, especially as groundwater demand increases and aquifer recharge suffers due to climate change. “Germany could benefit from the experience gained in southwestern Europe, how groundwater can be optimally used, which irrigation methods are more effective, how we enhance stakeholder engagement and what mistakes should be avoided in the future," says Seifeddine Jomaa. One thing is clear: Germany needs an anticipatory approach for sustainable groundwater use.
PAPER: http://dx.doi.org/10.1038/s43247-024-01554-w