Today, and for the past several million years, Earth's climate has been characterized by large-scale glaciation, although we currently live in an interglacial of this geologically rare state. Earth's last major glaciation, the Late Paleozoic Ice Age, occurred 300 million years ago. During this time, the continents assembled into the supercontinent Pangaea; sediments from the southern high latitudes preserve abundant evidence for large-scale glaciation. Geoscientists have long presumed that, like today, the tropics remained warm throughout this glaciation, but new evidence from the western United States -- paleo-tropical Pangaea -- indicate that cold temperatures gripped the low latitudes. Soreghan et al. found this evidence in the remarkable preservation of a 300 million-year-old glacial landscape and associated glacial sediments in western Colorado. Owing to the close proximity of the glacier to ancient sea level, the toe of the ice is estimated to have reached within less than 500 meters of elevation -- much lower than tropical glaciers of Earth's recent glacial states. Moreover, the Late Paleozoic preserves the only known occurrence of widespread tropical loess (windblown silt) in Earth's history, which is apparently of glacial derivation. Climate model simulations are unable to replicate such cold tropical conditions, even after incorporating the low atmospheric CO2 and reduced solar luminosity of the time. We are left with the prospect that what has been termed our "best-known" analogue to Earth's "modern" glaciation is poorly known, and Earth's climate system works in ways that remain elusive.
Microbes produce nanobacteria-like structures, avoiding cell entombment
Tomaso Bontognali et al., Geologisches InstitutCHN E 65, Universitatstrasse 16, 8092 Zurich, Switzerland. Pages 663-666.
Particles shaped like fossils of
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