Latest maps of 8th continent + Best hidden impact craters + Why rare earth elements?

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The latest maps of the world's eighth continent
https://www.bbc.com/future/article/20230...-continent

EXCERPTS: Today, schoolchildren, explorers and politicians generally accept the neat division of the world's ground into these simple units, which include Europe, Asia, Africa, North America, South America, Australia, and Antarctica.

But in 2017, the story took an unexpected turn – the seven-continent model has been a mistake all along. Enter Zealandia, a long-lost land to the southeast of Australia, otherwise known as the planet's forgotten eighth continent. Scientists had long predicted the existence of this bonus southern landmass, but it remained missing for 375 years – largely because it’s almost entirely submerged under 1-2 km (0.6-1.2 miles) of water. Now they are beginning to unravel its secrets.

This month, an international team of researchers released the most detailed maps of Zealandia to date – incorporating all five million square kilometres (two million sq miles) of this underwater region and its geology. In the process, they have uncovered hints as to how this mysterious continent formed – and why it has been obscured beneath the waves for the last 25 million years.

[...] It's thought that all or part of Zealandia may have existed as an island for a while. But then around 25 million years ago, it was disappeared beneath the ocean... (MORE - missing details)


The eight best hidden impact craters on Earth
https://daily.jstor.org/the-eight-best-h...-on-earth/

INTRO: The solar system can be a violent place. When we look at bodies like the Moon or Mercury, we see that they are peppered by the meteor impacts of many eons. On Earth, though, evidence of collisions is rare. Sure, there’s the famous Meteor Crater in Arizona, and perfectly circular lakes that are in fact water-filled impact craters. But for the most part, craters on our planet have been erased by wind, rivers, or rain—things you will not see on Mercury or the Moon.

But that’s not all. Some craters have vanished altogether, subducted into the Earth through plate tectonics. Others are hiding under an ice sheet. Still others lie at the bottom of the ocean or under layers of sediment. Some craters are just plain remote, or rest in thickly forested areas. Because of this, many craters on Earth have escaped detection until recently.

There are many ways to find craters, but only a few signs that confirm them. “The gold standard is to find shocked quartz in the crater itself,” Brandon Johnson, an associate professor in the Department of Earth, Atmospheric, and Planetary Sciences at Purdue University, explained to Big Think. Johnson is referring to small grains with features that indicate the rock experienced a sudden increase in pressure, which is indicative of an impact event. Other features, he explained, are shatter cones—very rare, cone-shaped features that are formed by a high-velocity shock wave and are only found under an impact site of a meteor or that of a nuclear blast. Then there are microscopic grains of rocks called high-pressure polymorphs, a variation of the crystal structure of a mineral that forms at high pressures. “If you find any of those things in what you suspect to be a crater, that it essentially becomes a confirmed crater,” Johnson said.

Searching the Earth, then, we can find plenty of evidence that our planet underwent substantial bombardment from the Cosmos. Here are Big Think’s top eight hidden meteor craters...(MORE - details)

COVERED: The Hiawatha Glacier Impact Crater ........ The Chesapeake Bay Meteor Crater ........ The Sudbury Basin ........ Chicxulub, the Dinosaur killer ........ Nadir ........ Yilan Crater ........ A Meteoric Wine ........ S3: The Crater So Hidden, It Doesn’t Exist Anymore


Why are rare earth elements so rare?
https://www.livescience.com/planet-earth...ts-so-rare

INTRO: Rare earth elements have a number of useful properties that make them highly sought after by the tech and energy industries. This collection of 17 metals includes the 15 metallic elements found at the bottom of the periodic table, as well as the elements yttrium and scandium.

The most valuable of these are neodymium, praseodymium, terbium and dysprosium, which act as superstrong miniaturized magnets, a vital component of electronics, including smartphones, electric car batteries and wind turbines. However, their limited global supply is a big worry for governments and corporations that need these metals to continue manufacturing all sorts of modern essentials.

But why are the rare earth elements so rare?

It turns out, they're not really that rare. A U.S. Geological Survey study on the "crystal abundance" of different elements — meaning how much is available if you average out Earth's crust — found that most of the rare earths "are in the same order of magnitude as common metals like copper and zinc," Aaron Noble, a professor and head of the Mining and Mineral Engineering Department at Virginia Tech, told Live Science. "They're certainly not as rare as metals like silver, gold and platinum."

Although the elements are fairly common, they're very difficult to extract from their natural sources.

"The 'troublesome earths' would have been a better name," Paul Ziemkiewicz, director of the West Virginia Water Research Institute, told Live Science. "The problem is, they're just not that concentrated in one place. There are around 300 milligrams per kilogram [0.005 ounces per pound] of rare earths across all shale in the United States. That's about what you'd get if you dug a hole in your backyard." (MORE - details)
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