The role of geomagnetic field intensity in late Quaternary evolution of humans and large mammals
A recent study by James Channell and L. Vigliotti published in Reviews of Geophysics outlines possible linkages between the intensity of the Earth’s magnetic field and human and mammal evolution.
The strength of Earth’s magnetic field in the past, recorded by rocks and sediments, provides a proxy for past flux of ultra-violet radiation (UVR) to Earth’s surface due to the role of the field in modulating stratigraphic ozone. About 40 thousand years ago, mammalian fossils in Australia and Eurasia record an important die-off of large mammals that included Neanderthals in Europe. In the Americas and Europe, a large mammalian die-off appears to have occurred ~13 thousand years ago. Both die-offs can be linked to minima in Earth’s magnetic field strength implying that UVR flux variations to Earth’s surface influenced mammalian evolution. For the last ~200 thousand years, estimates of the timing of branching episodes in the human evolutionary tree, from modern and fossil DNA and Y-chromosomes, can be linked to minima in field strength which implies a long-term role for UVR in human evolution. New fossil finds, improved fossil dating, knowledge of the past strength of Earth’s magnetic field, and refinements in the human evolutionary tree, are sharpening the focus on a possible link between UVR arriving at the Earth’s surface, magnetic field strength, and events in mammalian evolution.
It was a busy first week for students attending the UF in Merida (Yucatan, Mexico) Program. After arriving in Merida on the evening of June 17, students met on Monday (June 19) at the Centro Institucional de Lenguas, where they study Spanish.
On Wednesday, they headed for the town of Izamal, where they visited a technical university, interacted with local students, reaped the benefits of the culinary arts program, and encountered some of the gaily decorated horses and carriages in the main square (Photos 3-5).
On Friday, it was off to the organic farm of Dr. Juan Jimenez, where students learned about cultivating dragon fruit, a native climbing cactus that blooms for one night only. It is know locally by its Maya name, pitaya. The UF students also instructed a couple of students from the University of Yucatan on details of the “Gator Chomp”.
Then it was on to the town of Dzitya, where local artisans work with tropical hardwoods and local limestone. Although they use power tools today, they used to rely on more traditional tools to work wood, like the foot-operated lathe.
Next, it was off to the archaeological site of Dzibilchaltun, where the group visited the “Temple of the Seven Dolls” and saw some of the local fauna, such as the ubiquitous “black iguana.” Much as today, the ancient Maya “mined” the local rock to create their infrastructure, such as buildings and roads. As you look around Williamson Hall, note that so much of what you see ultimately came from the Earth (walls, windows, desks, light fixtures, tiles, bathroom sinks and toilets, etc.). Everyone was pleased to have the opportunity to take a dip in Cenote Xlakah, a sinkhole where the underlying aquifer is exposed.
The next day, it was off to the west coast, and the town of Celestun. Students toured the long coastal lagoon via boat, stopping at the “ruins” of an old village previously involved in salt production. Heavy rains made it necessary to wade along parts of the inundated old road. The lagoon is bounded by a barrier peninsula and rimmed by mangroves (4 species). The very productive coastal lagoon system is a source of aquatic resources (e.g. crabs) , and is home to a large population of flamingoes.
At Valdiocera Spring, which discharges into the lagoon, we had the good fortune to see a young tiger heron.
UF Geological Sciences PhD student Stephanie James has been advancing new methods to use seismic noise to monitor seasonal changes in depth to ice in Alaskan sediments. With co-authors from Sandia National Laboratory and UF, she recently published a paper “Improved moving window cross-spectral analysis for resolving large temporal seismic velocity changes in permafrost” in Geophysical Research Letters. This paper was selected as a recent “Editor’s Highlight”.
Stephanie James completed her PhD in May and received a National Science Foundation Postdoctoral Fellowship to continue her research in this field. She will be collaborating with researchers at the US Geological Survey in Colorado.