Links: Human Brain Evolution, Pyrometamorphism, Upper Atmosphere Cooling

I learned some new things from these articles over the past couple of weeks.

1) Endocranial Volumes and Human Evolution: Warning- this figure posted below is deceptive!

Although hominin brain volumes increase over a 7 million year history, patterns of growth in separate lineages show, both, stasis & episodic increase. In an excellent analysis, anthropologist Ian Tattersall shows that a trend towards large brain volume is expressed independently in three separate hominin lineages, raising important questions about the role of social interactions and environmental pressure that could lead to the evolution of larger brain size. And most intriguingly, brain volume size has decreased in the Homo sapiens lineage over the past few tens of thousands of years. What does it mean for the evolution of complex behavior and symbolism?

2) Scorched Minerals in Sedimentary Rocks: Petrologist Michael Anenburg reports a most unusual suite of minerals. They formed by pyrometamorphism, i.e., the transformation of sedimentary rocks by heat supplied by large fires. This process takes place at or very near the surface, likely driven by the ignition of oil bearing shales or coal seams. The rocks described here are from the Dead Sea area of Israel. Before metamorphism, they were a sequence of impure limestones and phosphorites. There is a memorable description of these combusted limestones in the paper; 

" Gross discovered that the Hatrurim Formation was fundamentally a natural Portland cement factory. Indeed, many of the synthetic compounds found in cement occur naturally in the Hatrurim Formation and were subsequently named after the local Hebrew or Arabic place names in which they were found, such as hatrurite, ye’elimite, and harmunite. Concrete is formed when Portland cement is mixed with water, and the pyrometamorphic minerals of the Hatrurim Formation have experienced a similar process. Hundreds of thousands to millions of years of exposure to rain and groundwater has led to the hydration and alteration of most of the high temperature minerals. The end result is essentially a naturally formed concrete". 

3) The Upper Atmosphere Is Cooling, Prompting New Climate Concerns: The earth's atmosphere is layered. While the lowermost  layer known as the troposphere is warming as we emit more and more carbon dioxide, satellite data shows that the two uppermost layers, the mesosphere and the thermosphere have cooled by 3.1 deg F between 2002 and 2019. Scientists worry about the impact of this cooling on weather patterns on earth. A succinct summary by Fred Pearce.

 

Author Contact: suvrat_k@yahoo.com