Privileged Planet: new study of Earth's core (Introduction)

by David Turell , Monday, July 15, 2019, 05:23 (1749 days ago) @ David Turell

Based on isotopic findings to analyze the core as best we can:

https://cosmosmagazine.com/earth-sciences/earth-s-core-has-been-leaking-for-billions-of...

"Earth’s magnetic field protects and makes our planet habitable by stopping harmful high-energy particles from space, including from the Sun. The source of this magnetic field is the core at the centre of our planet.

"But the core is very difficult to study, partly because it starts at a depth of about 2,900 kilometres, making it too deep to sample and directly investigate.

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"The core is the hottest part of our planet with the outer core reaching temperatures of more than 5,000℃. This has to affect the overlying mantle and it is estimated that 50% of volcanic heat comes from the core.

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"Our findings suggest some core material does transfer into the base of these mantle plumes, and the core has been leaking this material for the past 2.5 billion years.

"We discovered this by looking at very small variations in the ratio of isotopes of the element tungsten (isotopes are basically versions of the same element that just contain different numbers of neutrons).

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"Tungsten (chemical symbol W) as the base element has 74 protons. Tungsten has several isotopes, including 182W (with 108 neutrons) and 184W (with 110 neutrons).

"These isotopes of tungsten have potential to be the most conclusive tracers of core material, because the mantle is expected to have much higher 182W/184W ratios than the core.

"This is because of another element, Hafnium (Hf), which does not dissolve in iron-nickel alloy and is enriched in the mantle, and had a now-extinct isotope (182Hf) that decayed to 182W. This gives the mantle extra 182W relative to the tungsten in the core.

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"Our study shows a substantial change in the 182W/184W ratio of the mantle over Earth’s lifetime. Earth’s oldest rocks have significantly higher 182W/184W than than most rocks of the modern-day Earth.

"The change in the 182W/184W ratio of the mantle indicates that tungsten from the core has been leaking into the mantle for a long time.

"Interestingly, in Earth’s oldest volcanic rocks, over a time frame of 1.8 billion years there is no significant change in the mantle’s tungsten isotopes. This indicates that from 4.3 billion to 2.7 billion years ago, little or no material from the core was transferred into the upper mantle.

"But in the subsequent 2.5 billion years, the tungsten isotope composition of the mantle has significantly changed. We infer that a change in plate tectonics, towards the end of the Archean Eon from about 2.6 billion years ago triggered large enough convective currents in the mantle to change the tungsten isotopes of all modern rocks.

"If mantle plumes are ascending from the core-mantle boundary to the surface, it follows that material from Earth’s surface must also descend into the deep mantle.

"Subduction, the term used for rocks from Earth’s surface descending into the mantle, takes oxygen-rich material from the surface into the deep mantle as an integral component of plate tectonics.

"Experiments show that increase in oxygen concentration at the core-mantle boundary could cause tungsten to separate out of the core and into the mantle. "

Comment: This shows how specially constructed our planet is with its special layers. The core creates our protective magnetic field shield. Subduction contributes to several important feed back controls to stabilized the Earth's environment.