Massive projectiles striking much larger bodies create various kinds of craters, including multi-ring basins–the largest geologic features observed on planets and moons. In such collisions, the impactor is completely destroyed and its material is incorporated into the larger body. Collison’s between bodies of comparable size, on the other hand, have very different consequences: one or both bodies might be entirely smashed, with mass from one or both the bodies redistributed among new objects formed from the fragments. Such a titanic collision between Earth and a Mars-size impactor may have given rise to Earth’s Moon.
Cuts that need to be held closed in order to heal properly have generally been held closed with stitches. However, pressure to reduce medical costs is mounting. Consequently, it is likely that a newly developed adhesive will become the routine method of holding most types of cuts closed. The new adhesive holds most types of cuts closed as well as stitches do, and the cost of applying it is comparable to that of closing cuts with stitches. But whereas stitches must generally be removed by medical personnel after the cut has healed, the adhesive simply wears off. Thus, for any cut that the adhesive can hold closed as well as stitches can, it is more economical to use the adhesive.
Astronomers have had difficulty accounting for certain planets discovered outside our solar system. They are called hot Jupiters because each is similar in mass to Jupiter, the largest solar-system planet, but orbits its parent star at a fraction of the distance at which Earth, let alone Jupiter, orbits the Sun. In the standard, solar-system-based theory of planetary formation, such a massive planet could not form so close to a star. So most attempts to explain a hot Jupiter’s existence envision it forming farther away, then migrating inward. According to one hypothesis, the planet’s gravitational field tugs on the protoplanetary disk of dust and gas from which it formed. The disk exerts its own gravitational tug, and this interplay of forces robs the planet of momentum in its orbital path, forcing it to spiral in toward the star.
Recent studies of ancient Maya water management have found that the urban architecture of some cities was used to divert rainfall runoff into gravity-fed systems of interconnected reservoirs. In the central and southern May Lowlands, this kind of water control was necessary to support large populations throughout the year due to the scarcity of perennial surface water and the seasonal availability of rainfall. Some scholars argue that the concentration of water within the urban core of these sites provided a centralized source of political authority for Maya elites based largely on controlled water access. Such an argument is plausible, however, it is less useful for understanding the sociopolitical implications of water use and control in other, water-rich parts of the Maya region.
Ralph Ellison was passionately interested in visual arts. He immersed himself in Harlem’s art scene in the 1930s, even apprenticing with sculptor Richmond Barthe for a time. Yet he was wary of projects aiming to provide a visual rendering of his novel Invisible Man. He reluctantly allowed Franklin Library to publish two illustrated versions of the novel but found the results disappointing and repeatedly rejected proposed film versions of the book. Despite his involvement in visual arts, Ellison insisted that only language could capture the complexity of American identity. This complexity consisted of the tension arising from the collision of the United States’ written ideals, as outlined in the founding documents, and the historical and contemporary experience molding the national consciousness.
What accounts for the low-lying, flat surface of Mars’s north? On Earth’s surface, higher- and lower-lying areas have different types of crust: one, thin and dense, is pulled toward Earth’s center more strongly by gravity, and the planet’s water naturally comes to sit over it, creating oceans. The processes that generate this oceanic crust drive plate tectonics.
Is Mars’s north similarly characterized by a sort of crust different from other areas of the planet? Some researchers do see signs of tectonic activity surrounding the northern basin that suggest that it was created through the formation of new crust, like ocean basins on Earth. However, McGill points to Northern bedrock structures that predate the features said to mark the start of the tectonic process. McGill instead believes that through some novel mechanism the ancient surface sank to its current depth as a single unit. This would explain why features around the basin’s edge, which would have formed as the surface dropped, seem to be younger than structures at its floor.
Some archaeologists speculate that the Americas might have been initially colonized between 40,000 and 25,000 years ago. However, to support this theory it is necessary to explain the absence of generally accepted habitation sites for that time interval in what is now the United States. Australia, which has a smaller land area than the United States, has many such sites, supporting the generally accepted claim that the continent was colonized by humans at least 40,000 years ago. Australia is less densely populated (resulting in lower chances of discovering sites) and with its overall greater aridity would have presented conditions less favorable for hunter-gatherer occupation.
W.E.B. Du Bois’ exhibit of African American history and culture at the 1900 Paris Exposition Universelle attracted the attention of a world of sociological scholarship whose value his work challenged. Du Bois believed that Spencerian sociologists failed in their attempts to gain greater understanding of human deeds because their work examined not deeds but theories and because they gathered data not to affect social progress but merely to theorize. In his exhibit, Du Bois sought to present cultural artifacts that would shift the focus of sociology from the construction of vast generalizations to the observation of particular, living individual elements of society and the working contributions of individual people to a vast functioning social structure.