Endosymbiosis – The Appearance of the Eukaryotes
Investigating the Cryogenian Ice Age led to finding evidence of runaway effects causing dramatic environmental changes, and the Cryogenian Ice Age’s dynamics will be investigated and debated for many years. The position of Antarctica at the South Pole and the landlocked Arctic Ocean have been key variables in initiating the current ice age, and another continental configuration that could contribute to initiating an ice age is , which and . A hypothesis is that can accompany supercontinents, so warm water is not pushed to the poles as vigorously. A supercontinent near the equator would not normally have ice sheets, which means that would be enhanced and remove more carbon dioxide than usual. Those conditions could initiate an ice age, beginning at the poles. It would start out as sea ice, floating atop the oceans.
Endosymbiotic Theory Introduction
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 .
Those interrelated and often mutually reinforcing lines of evidence have made many scientific findings difficult to deny. The ever-advancing scientific toolset, and the ingenuity of scientists developing and using them, and particularly the multidisciplinary approach that scientists and scholars are increasingly using, have made for radical changes in how we view the past. Those radical changes will not end any time soon, and what follows will certainly be modified by new discoveries and interpretations, but I have tried to stay largely within the prevailing findings, hypotheses, and theories, while also poking into the fringes and leading edges somewhat. Any mistakes in fact or interpretation in what follows are mine.
Biology Test 1 Flashcards | Quizlet
In 1967 she proposed a contentious new hypothesis whichbecame her most important scientific contribution as the endosymbiotic theoryof the origin of mitochondria as separate organisms that long ago entered a symbioticrelationship with eukaryotic cells through endosymbiosis.
"She is best known for her theory of symbiogenesis, which challenges a centraltenet of neodarwinism.
Energy and the Human Journey: Where We Have Been; …
Kirschvink noted that reappeared in the geological record during the possible Snowball Earth times, after vanishing about a billion years earlier. Kirschvink noted that iron cannot increase to levels where they would create BIFs if the global ocean was oxygenated. Kirschvink proposed that the sea ice not only killed the photosynthesizers, but it also separated the ocean from the atmosphere so that the global ocean became anoxic. Iron from volcanoes on the ocean floor would build up in solution during the , and during the greenhouse phase the oceans would become oxygenated and the iron would fall out in BIFs. Other geological evidence for the vacillating icehouse and greenhouse conditions was the formation of cap carbonates over the glacial till. It was a global phenomenon; wherever the Snowball Earth till was, cap carbonates were atop them. In geological circles, deposited during the past 100 million years are considered to be of tropical origin, so scientists think that the cap carbonates reflected a tropical environment. The fact of cap carbonates atop glacial till is one of the strongest pieces of evidence for the Snowball Earth hypothesis. Kirschvink finished his paper by noting that the eon of complex life came on the heels of the Snowball Earth, and scouring the oceans of life would have presented virgin oceans for the rapid spread of life in the greenhouse periods, and this could have initiated the evolutionary novelty that led to complex life.
Fermentation, mitochondria and regulation | Biology …
Part of the hypothesis for skyrocketing oxygen levels during the late Proterozoic was that high carbon dioxide levels, combined with a continent that had been ground down by glaciers, and the resumption of the hydrological cycle, which would have vanished during the Snowball Earth events, would have created conditions of dramatically increased erosion, which would have buried carbon (the cap carbonates are part of that evidence) and thus helped oxygenate the atmosphere. Evidence for that increased erosion also came in the form of strontium isotope analysis. Two of strontium’s stable isotopes are . Earth’s mantle is enriched in strontium-86 while the crust is enriched in strontium-87, so basalts exposed to the ocean in the oceanic volcanic ridges are enriched in strontium-86 while continental rocks are enriched in strontium-87. If erosion is higher than normal, then ocean sediments will be enriched in strontium-87, which analysis of Ediacaran sediments confirmed. That evidence, combined with carbon isotope ratios, provides a strong indication of high erosion and high carbon burial, which would have increased atmospheric oxygen levels. There is other evidence of increasing atmospheric oxygen content during the late Proterozoic, such as an increase in rare earth elements in Ediacaran sediments. Although there is still plenty of controversy, today's consensus is that the Cryogenian is when , where they have largely stayed, although as this essay will later discuss, oxygen levels have varied widely since the late Proterozoic (from perhaps only a few percent to 35%).