Latest news with #Phanerozoic
Forbes
3 days ago
- Science
- Forbes
Scientists Reconstruct 540 Million Years Of Climate And Sea Level Change
Climate curve and sea level curve Two new studies offer the most detailed glimpse yet of how Earth's climate and sea levels have changed during the Phanerozoic — the latest geologic eon covering the time period from 538.8 million years ago to the present. The first curve reveals that Earth's temperature has varied more than previously thought over much of the Phanerozoic eon and also confirms that Earth's temperature is strongly correlated to carbon-dioxide levels in the atmosphere. The team from Arizona compiled more than 150,000 published data points, their colleagues at the University of Bristol generated more than 850 model simulations of what Earth's climate could have looked like at different periods based on continental position and atmospheric composition. Using special data assimilation protocolls, the different datasets were combined to create an accurate curve of how Earth's temperature has varied over the past 485 million years. The climate curve reveals that temperature varied more greatly than previously thought. It starts with the Hirnantian, a period of major climatic oscillation lasting from approximately 460 to around 420 million years. The coldest period in the analyzed timescale is the Karoo glaciation, lasting from approximately 360 to 260 million years. But overall, the Phanerozoic was characterized by mild to warm climates, with global mean surface temperatures spanning from 52 to 97 degrees Fahrenheit (or 11 to 36 degrees Celsius). In the warmest periods global temperatures did not drop below 77 degrees Fahrenheit (25 degrees Celsius). In the last 60 million years, after a peak during the "Cretaceous Hothouse," Earth started to cool down. The global average temperature today is about 59 degrees Fahrenheit (15 degrees Celsius). The authors also note that the periods of extreme heat were most often linked to elevated levels of the greenhouse gas carbon-dioxide in the atmosphere. The second curve shows how sea levels correlate both with tectonic activity - closing or opening oceanic basins and shifting continents - and the climate, determining how much water is trapped in ice caps or glaciers. 'Plate tectonics determines the depth of the oceans. If the 'bathtub' becomes shallower, then the water level will rise. Ice caps on continents withhold water from the ocean, but when the ice melts, the 'bath water level' will rise, " explains study lead author Dr. Douwe van der Meer, guest researcher at Utrecht University. To assess sea level changes, the scientists looked at the prevailing sediment type deposited at the time. Claystone typically forms in deeper marine settings, while sandstone is deposited in shallow basins. This preliminary curve was then combined with data derived from fossils and paleogeographic simulations, visualizing the distribution of land and sea during different geological periods. The scientists were also able to estimate the location and volume of continental ice caps based on Earth's changing climate over time and the position of the continents in relation to the poles. Sea levels were relatively low during the first 400 million years, reflecting the cooler climate and low tectonic activity. During the Carboniferous (358-298 million years ago) there were very large sea level variations due to a large ice cap covering a large landmass in — called Gondwana by geologists — the southern hemisphere. During the Cretaceous (145-66 million years ago) the supercontinent of Pangaea started to break up and the hothouse climate caused the poles to be ice free. These two effects resulted in global sea levels being more than 200 meters higher than they are at present. In the last 60 million years Earth started to cool down and around 30 million years ago the first ice sheets started to form on the poles. In the past 2 million years during the last major ice ages sea levels dropped up to 100 meters. The climate study, "A 485-million-year history of Earth's surface temperature," was published in the journal Science and can be found online here. The sea level study, 'Phanerozoic orbital-scale glacio-eustatic variability,' was published in the journal Earth and Planetary Science Letters and can be found online here. Additional material and interviews provided by University of Utrecht.
Yahoo
21-02-2025
- Science
- Yahoo
Why is there so much gold in west Africa?
Militaries that have taken power in Africa's Sahel region – notably Mali, Burkina Faso and Niger – have put pressure on western mining firms for a fairer distribution of revenue from the lucrative mining sector. Gold is one of the resources at the heart of these tensions. West Africa has been a renowned gold mining hub for centuries, dating back to the ancient Ghana empire, which earned its reputation as the 'Land of Gold' because of its abundant reserves and thriving trade networks. The region remains a global leader in gold production. As of 2024, west Africa contributed approximately 10.8% of the world's total gold output. But why is there so much gold in this region? The Conversation Africa asked geologist Raymond Kazapoe to explain. The simple answer here is that we are not certain. However, scientists have some ideas. Gold, like all elements, formed through high energy reactions that occurred in various cosmic and space environments some 13 billion years ago, when the universe started to form. However, gold deposits – or the concentration of gold in large volumes within rock formations – are believed to occur through various processes, explained by two theories. The first theory – described by geologist Richard J. Goldfarb – argues that large amounts of gold were deposited in certain areas when continents were expanding and changing shape, around 3 billion years ago. This happened when smaller landmasses, or islands, collided and stuck to larger continents, a process called accretionary tectonics. During these collisions, mineral-rich fluids moved through the Earth's crust, depositing gold in certain areas. A newer, complementary theory by planetary scientist Andrew Tomkins explains the formation of some much younger gold deposits during the Phanerozoic period (approximately 650 million years ago). It suggests that as the Earth's oceans became richer in oxygen during the Phanerozoic period, gold got trapped within another mineral known as pyrite (often called fool's gold) as microscopic particles. Later, geological processes – like continental growth (accretion) and heat or pressure changes (metamorphism) released this gold – forming deposits that could be mined. Most gold production and reserves in west Africa are found within the west African craton. This is one of the world's oldest geological formations, consisting of ancient, continental crust that has remained largely unchanged for billions of years. The craton underlies much of west Africa, spanning parts of Mali, Ghana, Burkina Faso, Côte d'Ivoire, Guinea, Senegal and Mauritania. In fact, most west African countries that have significant gold deposits have close to 50% of their landmass on the craton. Notably, between 35% and 45% of Ghana, Mali and Côte d'Ivoire's territory sits on it – which is why these areas receive so much attention from gold prospectors. Gold deposits were formed within west Africa's craton rocks during a major tectonic event, known as the Eburnean Orogeny, 2.2 billion to 2.08 billion years ago. This event was accompanied by the temperature, pressure and tectonic conditions which promote gold mineralisation events. Most of the gold resources in the west African craton are found within ancient geological formations formed by volcanic and tectonic processes about 2.3 billion to 2.05 billion years ago. These are known as the Rhyacian Birimian granitoid-greenstone belts. These gold-bearing belts in Ghana and Mali are by far the most endowed when compared with other countries in the region. Ghana and Mali currently, cumulatively account for over 57% of the combined past production and resources of the entire west Africa sub-region. Ghana is thought to be home to 1,000 metric tonnes of gold. The country produces 90 metric tonnes each year – or 7% of global production. Gold production in Mali reached around 67.7 tonnes in 2023. Mali has an estimated 800 tons of gold deposits. By comparison, the world's two largest gold producers are China (which mined approximately 370 metric tonnes of gold in 2023) and Australia (which had an output of around 310 metric tonnes in 2023). Gold was traditionally found by panning in riverbeds, where miners swirled sediment in water to separate the heavy gold particles, or by digging shallow pits to extract gold-rich ores. Over time, methods have evolved to include geochemical exploration techniques, advanced geophysical surveys, and chemical extraction techniques, like cyanide leaching. Geological mapping techniques are always evolving, and at the moment, there is a lot of interest in combining remote sensing data with cutting-edge data analytics methods, like machine learning. By combining these two methods, geologists can get around some of the problems caused by traditional methods, like the reliance on subjective judgement to create reliable maps and the need to spend money prospecting in areas with low chances of success. In recent years, deep learning computer techniques have made significant progress. They examine various geological data-sets to reduce uncertainty and increase the chances of finding gold mineralisation through advanced artificial intelligence techniques. These methods have proved highly beneficial in identifying specific features and discovering new mineral deposits when applied to remote sensing data. Another method, which I've researched and which could serve as a complementary gold exploration tool, is the use of stable isotopes. Stable isotopes are elements – like carbon, hydrogen and oxygen – that do not decay over time. Some are responsible for helping to carry gold, in fluids, through rocks to form the deposits. As the gold-bearing fluids interact with the rocks, they transfer the stable isotopes to the rocks, thereby imbuing them with their unique signature. The thinking here is to identify the signature and then use it as a proxy for finding gold, since gold itself is hard to identify directly. Advancements in analytical techniques have reduced the cost, volume, and time involved. This makes it a viable alternative to geochemical approaches – the most widely used and relatively efficient method. This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Raymond Kazapoe, University for Development Studies Read more: A new report card shows inequality in Australia isn't as bad as in the US – but we're headed in the wrong direction West Africans have a high risk of kidney disease – new study confirms genetic cause Ghana's urban strategies neglect the needs of street vendors: policy must catch up with reality Raymond Kazapoe receives funding from the African Union and Pan African University to carry out some of the research referenced in this article
