Evidence of human occupation in Mexico around the Last Glacial Maximum

The initial colonization of the Americas remains a highly debated topic1 , and the exact timing of the frst arrivals is unknown. The earliest archaeological record of Mexico—which holds a key geographical position in the Americas—is poorly known and understudied. Historically, the region has remained on the periphery of research focused on the frst Americanpopulations2 . However, recent investigations provide reliable evidence of a human presence in the northwest region of Mexico3,4 , the Chiapas Highlands5 , Central Mexico6 and the Caribbean coast7–9 during the Late Pleistocene and Early Holocene epochs. Here we present results of recent excavations at Chiquihuite Cave—a high-altitude site in central-northern Mexico—that corroborate previous fndings in the Americas10–17of cultural evidence that dates to the Last Glacial Maximum (26,500–19,000years ago)18, and which push back dates for human dispersal to the region possibly as early as 33,000–31,000years ago. The site yielded about 1,900stone artefacts within a 3-m-deep stratifed sequence, revealing a previously unknown lithic industry that underwent only minor changes over millennia. More than 50radiocarbon and luminescence dates provide chronological control, and genetic, palaeoenvironmental and chemical data document the changing environments in which the occupants lived. Our results provide new evidence for the antiquity of humans in the Americas, illustrate the cultural diversity of the earliest dispersal groups (which predate those of the Clovis culture) and open new directions of research

KSArray: A Portable Seismic Network in the Heart of the Conterminous United States

Since early July, 2000, we have been conducting an NSF-funded portable seismic experiment across Kansas. The major scientific goals of the experiment include 1). deep structure of the 1.1 billion years old, 2000 km long Midcontinental rift; 2). the mantle signature of the transition from the Rocky Mountains to the Great Plains; 3). crustal structure and micro-seismicity in the Manhattan, KS, area where two intensity 7-8 historical earthquakes have occurred in 1867 and 1906. 4). filling a seismic gap in the US and making it possible for combining data sets collected in the western and eastern parts of the United States. The experiment has two phases. Phase one is an 8-station STS2 broadband experiment along an E-W profile of about 370 km, approximately at the latitude of N39.5 degrees. The station at the western end of the profile is located near the easternmost station of the 1995 Rocky Mountain Front experiment (less than 1 km apart). Phase two is planned to start in early October and will consist of about 10 short-period, 3-component stations in a 100 by 100 km area around Manhattan, KS. Both phases are expected to record continuously at a rate of 20 samples per second for a period of 6 months. Preliminary analysis of data from the first several weeks of deployment indicates that the mantle beneath the Phase one array is anisotropic with the majority of the fast polarization directions being NE and splitting times about 0.6 s. The teleseismic P-wave travel time residuals relative to IASP91 shows a delay of 0.5 to 2 seconds at the westernmost station relative to the easternmost one. The Midcontinental rift corresponds to a localized delay of about 0.5 to 1 second. The verification of those preliminary observations and their tectonic implications will be presented

Evidence of human occupation in Mexico around the Last Glacial Maximum.

The initial colonization of the Americas remains a highly debated topic1, and the exact timing of the first arrivals is unknown. The earliest archaeological record of Mexico-which holds a key geographical position in the Americas-is poorly known and understudied. Historically, the region has remained on the periphery of research focused on the first American populations2. However, recent investigations provide reliable evidence of a human presence in the northwest region of Mexico3,4, the Chiapas Highlands5, Central Mexico6 and the Caribbean coast7-9 during the Late Pleistocene and Early Holocene epochs. Here we present results of recent excavations at Chiquihuite Cave-a high-altitude site in central-northern Mexico-that corroborate previous findings in the Americas10-17of cultural evidence that dates to the Last Glacial Maximum (26,500-19,000 years ago)18, and which push back dates for human dispersal to the region possibly as early as 33,000-31,000 years ago. The site yielded about 1,900 stone artefacts within a 3-m-deep stratified sequence, revealing a previously unknown lithic industry that underwent only minor changes over millennia. More than 50 radiocarbon and luminescence dates provide chronological control, and genetic, palaeoenvironmental and chemical data document the changing environments in which the occupants lived. Our results provide new evidence for the antiquity of humans in the Americas, illustrate the cultural diversity of the earliest dispersal groups (which predate those of the Clovis culture) and open new directions of research