One of our recent GEITP emails involved the topic of divergence of Neanderthal and Denisovan hominins from the the line leading to modern Homo sapiens; this was followed by discussion about “archeological evidence (in present-day North Dakota) of a sudden mass extinction of virtually all of Earth’s life on land — caused by the Chicxulub impact (large meteorite striking the Yucatan Peninsula and Gulf of Mexico ~66 million years ago).” This topic is within our purview of gene-environment interactions, because all of life’s genomes are dramatically influenced by environmental signals such as near-extinctions of life on our planet caused by various catastrophes. These are examples of massive climate change (in contrast to miniscule effects of the “human carbon footprint” silliness being pushed by a political agenda).
The attached editorial describes “The Five Mass Extinction Events” that have resulted in serious impacts on evolution of life on Earth, each one reshaping the biosphere — by ending the success of an overwhelming proportion of species, thereby creating new ecological niches for organisms that later inhabited the planet. Understanding the cause, or causes, of these events might help humanity to think about how the biosphere responds to dramatic environmental change, and how insignificant humans are, in the face of the forces at play in the universe.
The [attached] article is an editorial concerning two reports in this issue of Science (22 Feb 2o19; 363: p. 862 & p. 866, considered outside the domain of GEITP), which any interested GEITP’er is invited to pursue further. Whereas the topic of this editorial is primarily about “trying to determine the trigger(s) of the K-Pg extinction (occurring at the Cretaceous-Paleogene Boundary, delineated by extinction of a large number of organisms worldwide, including all dinosaurs except the ancestor to birds)” — the figure on page 816 is a VERY INFORMATIVE time-line diagram. The diagram shows, since complex life began on Earth some 250 million years ago, asteroid impact and flood basalt emplacement periods that have been causally associated with environmental crises, including the five mass extinctions over this period. Except for the K-Pg extinction, the geologic record of the other four mass extinction events so far lacks evidence that they were caused by substantial impact of a meteorite.
DwN
Science 22 Feb 2o19; 363: 815-816