Saturday, 12 September 2020

Where Does the Carbon in Diamonds Come From?

Where Does the Carbon in Diamonds Come From? 

this week I found THIS ARTICLE on the Earth-logs blog. It is based on THIS PAPER. It was thought that the carbon came from subducted sedimentary rocks. Then we thought of the basalts in the oceanic crust. Their reaction with aqueous fluids results in carbonates.

Current research uses the isotopic chemistry of carbon and nitrogen in the diamonds and the tiny silicate minerals included in them. Most of these are garnets. From the studies the depth of formation can be indicated and this can help determine the carbon source.

And it seems that the oceanic basalts are the favoured source.

But VERY deep diamonds - formed below 660km - may be different. The isotopes suggest that the carbon source is within the mantle and ultimately the stellar dust that accreted to form the earth. But at that depth the carbon is incorporated in metals and carbides. The authors suggest that subducted slabs, reaching that depth, release watery fluids which mobilise the trapped carbon and allow the formation of diamond.

Diamond crystal containing a garnet and other inclusions (Credit: Stephen Richardson, University of Cape Town, South Africa)

Friday, 4 September 2020

Hibernation is Not New

 Hibernation is Not New

A correspondent brought THIS ARTICLE to my attention.

Lystrosaurus is the creature which survived the end-Permian mass extinction. In the Triassic they were found all over Gondwanaland. The specimens used in this study came from what is now Antarctica and South Africa. In Triassic times Antarctica was within the Antarctic Circle, South Africa outside it. 

Lystrosaurus is characterised by having tusks, which like elephants tusks, grow throughout their lives. And they have growth rings. The South African specimens have regularly spaced rings, the Antarctic ones have the same but also closely-spaced, thick rings.

a A cross-section of Antarctic specimen UWBM 118025 with a “hibernation zone” highlighted at a higher magnification. Scale bars = 1000 μm. b Well-preserved regular incremental growth marks from the South African specimen UWBM 118028, lacking “hibernation zones”. Arrows denote individual lines with an average spacing of 16–20 μm. Scale bar = 100 μm.

The authors argue that this indicates the Antarctic creatures were hibernating - or something very like it. Which is not really surprising but nice to have some evidence for it.

The original article is HERE.

Tuesday, 1 September 2020

Methane Outgassing in Siberia

 Methane Outgassing in Siberia

By chance I came across THIS STORY in the Siberian Times. it seems, that with global warming methane is being released by the permafrost, often with spectacular results.

 The new funnel filmed from air by the team of Yamal-based TV station. Picture from July 2020 by Vesti Yamal. Note the figures for scale.

The other pictures in the article are equally spectacular. 

This is a rather worrying development. Methane is a more powerful greenhouse gas than carbon dioxide and there is believed to be vast quantities of it captured in the permafrost. If it continues to be released it will trigger a vicious circle.