Evidence for continental drift.
For this essay’s purposes, the most important ecological understanding is that the Sun provides all of earthly life’s energy, either (all except nuclear-powered electric lights driving photosynthesis in greenhouses, as that energy came from dead stars). Today’s hydrocarbon energy that powers our industrial world comes from captured sunlight. Exciting electrons with photon energy, then stripping off electrons and protons and using their electric potential to power biochemical reactions, is what makes Earth’s ecosystems possible. Too little energy, and reactions will not happen (such as ice ages, enzyme poisoning, the darkness of night, food shortages, and lack of key nutrients that support biological reactions), and too much (such as , ionizing radiation, temperatures too high for enzyme activity), and life is damaged or destroyed. The journey of life on Earth has primarily been about adapting to varying energy conditions and finding levels where life can survive. For the many hypotheses about those ancient events and what really happened, the answers are always primarily in energy terms, such as how it was obtained, how it was preserved, and how it was used. For life scientists, that is always the framework, and they devote themselves to discovering how the energy game was played.
Continental Drift - the evidence that supports the theory
Humans took a different path 2.5 mya. There are generally two schools of thought regarding the appearance of among scientists: one is called the Multiregional Model, and the other is called the . In their essence, the Multiregional Model had those migrants eventually evolving into today’s races, and the “Out of Africa” Model had humans evolve in Africa and then spread across the world and replace/displace all other members of the genus. The rise of has largely resolved the issue in favor of the “Out of Africa” Model. There are also intermediate views and variations of each hypothesis, which generally relate to the invaders mating with the natives, even if they could be classified as separate species. For instance, Neanderthal DNA is part of the human genome, which reflects interbreeding. Since Neanderthals were largely confined to Europe and what became the Fertile Crescent, and the migration of the original was from Africa, sub-Saharan Africans . Africans also have the most genetic divergence, which reflects the idea that humans have lived longer in Africa than anywhere else. There is virtually no doubt that evolved in Africa.
To revisit the Neanderthal split from about 500 kya, stayed in West Asia and Africa. When evidence of came to light, some scientists placed the beginning of the at about 500 kya. Stone tools have recently been dated using , which works for stone tools heated by fires, and using . That method measures water absorption into the surface of obsidian tools. For dating artifacts before the appearance of behaviorally modern humans about 70-50 kya, will not work, but successful. Neanderthals dominated Europe and today’s Middle East while home was Africa, and they also ranged to Europe and West Asia. Whether existed for only a half-million years or a million is controversial today, but what is not very controversial is that it is probably the direct ancestor of both Neanderthals and , and the first members of our species appeared in Africa about 200 kya. There is evidence that other descendants of may have existed, and . It also could have been a Neanderthal descendant. As with the discovery of the “” of Flores Island, it will not be surprising if scientists find more species that branched off of those early human and protohuman lines and died out when behaviorally modern humans spread across Africa and Eurasia.
Wegener's hypothesis of Continental Drift & evidence to ..
1910 American physicist and glaciologist Frank Bursley Taylor proposed the concept of 'continental drift' to explain the apparent geological continuity of the American Appalachian mountain belt (extending from Alabama to Newfoundland) with the Caledonian Mountains of NW Europe (Scotland and Scandinavia), which now occur on opposite sides of the Atlantic Ocean.
compelling evidence for his continental drift hypothesis ..
1912 Alfred Wegener reproposed the theory of continental drift. He had initially become fascinated by the near-perfect fit between the coastlines of Africa and South America, and by the commonality among their geological features, fossils, and evidence of a glaciation having affected these two separate continents. He compiled a considerable amount of data in a concerted exposition of his theory, and suggested that during the late Permian all the continents were once assembled into a supercontinent that he named Pangaea, meaning 'all Earth'. He drew maps showing how the continents have since moved to today's positions. He proposed that Pangaea began to break apart just after the beginning of the Mesozoic Era, about 200 Ma ago, and that the continents then slowly drifted into their current positions.
Plate Tectonics: 2.1 Continental drift - OpenLearn - …
1920-1960 A range of geophysical arguments was used to contest Wegener's theory. Most importantly, the lack of a mechanism strong enough to 'drive continents across the ocean basins' seriously undermined the credibility of his ideas. The theory of continental drift remained a highly controversial idea.
2 From continental drift to plate tectonics 2.1 Continental drift
1944 Wegener's theory was consistently championed throughout the 1930s and 1940s by Arthur Holmes, an eminent British geologist and geomorphologist. Holmes had performed the first uranium-lead radiometric dating to measure the age of a rock during his graduate studies, and furthered the newly created discipline of geochronology through his renowned book . Importantly, his second famous book did not follow the traditional viewpoints and concluded with a chapter describing continental drift.