Hotspots of Earth
To geologists, hotspots are places on Earth where it has been presumed that, deep down in the lower mantle, extremely high temperatures form plumes of magma rising from more-or-less stationary spots. Meanwhile, up above, the Earth’s crust oats atop the mantle and is constantly on the move thanks to plate tectonics. As a section of the mobile crust moves over a stationary hot mantle plume, you occasionally get a volcanic eruption as the hot plume makes it to the surface.
It’s a good theory that makes sense based on what we see on the surface of the Earth. But now, it may be a good theory in need of revision. Writing in the journal Science, a team of earth and planetary scientists led by Xiyuan Bao (UCLA) has found that not all hotspots are created equal. e team’s temperature inferences indicate only about half of plume-fed hotspots are indeed “hot-hot” whereas the other half are not. It may be that some hotspots do indeed originate deep down in the mantle, as always assumed, but others may originate in the upper mantle and require rethinking their origins and causes.
The Cenozoic strata of North America holds a long fossil record of true cats (felids) and cat-like species (nimravid feliforms) including the common house cat. But there was a 6.5 million year period some 25 to 18.5 million years ago with few to no cat or cat-like fossils all across the continent, a period commonly referred to as the “Cat Gap.” What caused it?
Now, paleontologist Paul Barrett (University of Oregon) suggests the gap “may be more taphonomic than evolutionary.” Taphonomy is the study of events and processes that lead to plants and animals being fossilized and preserved in sediments. Could it be that the environments haunted by cats in North America 25 to 18.5 million years ago just weren’t conducive to fossilization? By 18.5 million years ago, glaciation led to lower sea levels and paved the way for true cats, Pseudaelurus, to come across the Bering land bridge from Siberia to North America This gave us the common ancestor of our current cats and brought the “Cat Gap” to a close to kick off a long, successful reign.
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