John Erwin, Alexi Giannoulias, Dr.
The moon rocks retrieved by astronauts are still being tested, as new experiments and hypotheses are devised. In 2012, which resulted from testing moon rocks for the ratios (both are stable isotopes), and it has brought into question the hypothesis that the Moon was formed by a planetary collision more than four billion years ago. The titanium ratio was so much like Earth’s that a collision with Earth forming the Moon has been questioned (as very little of the hypothesized colliding body became part of the Moon). The collision hypothesis will probably survive, but it may be significantly different from today’s hypothesis. , as well as , and their ages confirm that geologists have derived, and meteorite dates provide more evidence that our .
George Mihel, Tom Pulver, John Sanders, Laurie Stone, Dr.
With the Eastern Woodlands’ tremendous forests, iron could be smelted with the preferred wood, and in 1810 the USA produced 45,000 metric tons of pig iron. As previously stated, the colonial era was marked early on by mercantilist practices. In Mesoamerica, where the first , royal monopolies in gold and silver, stealing arable land from the natives, and banning industries that could compete with those in Spain were predominant practices. When the British as their foothold in India, they immediately began to ban weaving and turn Bengal into a plantation to supply British mills. British soldiers eventually amputated the thumbs of Bengali weavers. When began agitating for freedom from the British, one of his campaigns was to replace imported British textiles.
Before the era of mass extinction investigation that began in the 1980s, a hundred hypotheses were presented in the scientific literature for the dinosaur extinction, but it was a kind of scientific parlor game. Scientists from all manner of specialties concocted their hypotheses. But even during the current era of scientific study of mass extinctions, much is unknown or controversial and even the data is in dispute, let alone its interpretation. Dynamics may have conflated to produce catastrophic effects, such as increasing atmospheric carbon dioxide concentration warming the land and oceans to the extent that otherwise stable on the ocean floor and in permafrost would be liberated and escape into the atmosphere. That situation is to the , , and extinctions, as well as helping end the . Today, there is genuine fear among climate scientists that , as global warming continues and hydrocarbons are burned with abandon, which could contribute to catastrophic runaway conditions. Wise scientists admit that humanity is currently conducting a huge chemistry experiment with Earth, and while the outcomes are far from certain, the .
John O'Keefe, Evelyn Phillips, Dr.
works for animals that are no more than a couple of millimeters thick, but for larger animals a respiration system was necessary. The rise of the arthropods has been an enduring problem for paleobiologists. Why was the arthropod so successful, particularly in the beginning? Segmented animals dominated Cambrian seas, and segmentation provides for repeated features. Segments obviously became important for locomotion but, for arthropods, segmentation appears to have conferred the more important advantage of distributed oxygen absorption. Each trilobite leg had an attached gill, and leg motion constantly drew fresh oxygenated water over each gill. Arthropods never developed the kinds of lungs that vertebrates have, or the pump gills of fish and other aquatic animals. Early arthropods breathed by moving their legs. Peter Ward’s recent hypothesis is that segments were first used for respiration, to provide a large gill surface area, and using the segments for locomotion came later. For trilobites, the same functionality that pushed water over gills was also coopted for food intake. Also, the leg-mounted gill was necessary because of an arthropod’s body armor; oxygen could not be absorbed through tough exoskeletons.
Eric Radtke, Marvin Scott, Dr.
The Cambrian’s global ocean contained far less oxygen than today’s. Being newly and probably inconsistently oxygenated by oceanic currents was only part of the problem. The Cambrian oceans were warmer than today’s oceans, perhaps far warmer, such as 40o C and higher for the . Water’s ability to absorb oxygen declines as it gets warmer. Water heated from 10o C to 40o C will lose 40% of its ability to absorb oxygen. The phenomenon of warmer water absorbing less oxygen contributed to many instances of anoxic waters during the eon of complex life, and particularly in the warmer, earlier periods.
William Simpson, Dennis Thompson, and Barbara Walters
Members of another phylum, , which superficially resemble clams, were successful in the Cambrian, but if their shells are opened, they look very different inside. Inside the shell is mostly empty space, with that perform a dual function of filtering food and absorbing oxygen. The cilia pump water through the shell and over the tentacles, which allows such animals to be immobile.