Answer and Explanation:
During the whole biota history, there occurred extinctions due to different reasons.
During the Cretaceous, which took place between 145-65 million years ago, there occurred a massive extinction that eliminated most of the species on the Earth. Many of the characteristic groups of this period were affected. Dinosaurs, Plesiosaurs, Ammonites, Tricodonts, Cycas, Gynkgos, Conifers, the recent angiosperms, birds, and mammals.
The extinction was caused by the volcanic eruptions, and the unusual fall of many different asteroids, which caused important changes on the Earth´s surface. The consequent climatic change was what ended affecting all the species directly. The extinction was gradual, although it occurred in a short geological lapse of time.
Answer:
During depolarization, the membrane potential rapidly shifts from negative to positive. As the sodium ions rush back into the cell, they add positive charge to the cell interior, and change the membrane potential from negative to positive.
Explanation:
The Earth was first considered habitable when we discovered that it was Microbial organisms that started the process. I would go with D.