Wipeout: the end-Permian mass extinction
Meanwhile, is crashing. As I have performed my studies since 1990, including numerous scientific topics, one issue became clear: biologists and climate scientists are in a panic regarding what is happening. Biologists know that they are living through the , which is caused by humans and is happening before their eyes. Climate scientists are watching humans alter the atmosphere to the extent that may be caused within a geologic timescale’s blink of an eye. It took more than two billion years for , and the , which took many millions of years to transpire. But humanity may end up altering the atmosphere so much in a mere few hundred years to actually turn Earth from an into a Greenhouse Earth, create and events, or myriad other potential outcomes. Industrial humanity is engaging in a chemistry and physics experiment with our home planet, and hardly anybody seems to notice or care. That frightens climate scientists, and biologists know that those potential geophysical events can make the current extinction event even more pronounced, and humans may achieve a mass extinction that exceeds even the , and do it quicker than every previous extinction event other than that . For one of many ominous trends, the oceans are being acidified by the increasingly acidic rain, which is . Peter Ward’s is not so farfetched, as he churns out grim books with his emeritus years not far off, but humans are the current agents of destruction, not Mother Earth and her other species. On , humanity is peering into the abyss.
What is one hypothesis for the mass extinction at the end of the ..
Whatever the causes were, the early Miocene was warm, and as with around the North Pole, migrating in the Arctic became easy again, and North America was invaded by Eurasian animals . The prominent descended from Asian migrants, and the strange-looking was also an Asian immigrant, which had claws on its forefeet, like a sloth’s. also migrated from Asia, and the arrived. Those North American days saw of a that was rhino-sized. A lived then, and the appeared in the early Miocene and migrated to Asia from North America. The general Oligocene cooling gave rise to tough, gritty plants, and deer, antelope, elephants, rodents, horses, camels, rhinos, and others developed , which had greatly expanded enamel surfaces for grinding those plants. Carnivores also migrated from Asia, such as , an , and . North America’s rodents and rabbits, , continued to diversify. Later in the Miocene’s warm period, the trickle of Asian immigrants became a flood, including a that weighed up to 600 kilograms (1,300 pounds), and two large groups of immigrant rhinos, and several genera , displaced endemic ones. In a late-Pliocene count of North American mammalian genera, a third were not native to North America. But North American fauna was unscathed compared to other continents. Below is an artist's conception of Miocene North America. (Source: public domain from Wikipedia)
In recent years, Neogene temperatures have been the focus of intensive research. What appears to be the proximate cause of elevated temperatures was a dramatic change in global ocean currents. The final closing of the , the isolation of Antarctica, the creation of , and the opening and closing of land bridges, such as in the Bering Sea and ultimately the land bridge between North and South America, created dramatic changes in ocean currents and global climate. One result was fluctuating . Its production declined beginning about 24 mya, and its weakness lasted until about 14 mya. Consequently, Earth’s oceans were not stratified as they are today, and warm water extended far lower into the oceans than it does today. Also, it reduced the temperature gradient between the equator and poles, which drives global currents: the greater the differential, the more vigorous the currents. It was still an Icehouse Earth, but the “mid-Miocene climatic optimum” was relatively warm. The past three million years are the coldest that Earth has seen since the that ended 260 mya, but this . While the steadily declining carbon dioxide levels of the past 150-100 million years is the ultimate cause of this Icehouse Earth phase, relatively short-term and regional fluctuations have had their proximate causes rooted in other geophysical, geochemical, and celestial dynamics.
the end-Cretaceous mass extinction.
As with the , the molecular evidence shows that virtually all major orders of mammals existed before the end-Cretaceous extinction. The Paleocene‘s Mammalian Explosion appears to have not been a genetic event, but an ecological one; mammals quickly adapted to empty niches that non-avian dinosaurs left behind. The kinds of mammals that appeared in the Paleocene and afterward illustrate the idea that body features and size are conditioned by their environment, which includes other organisms. With the sauropods' demise, high grazers of conifers never reappeared, but many mammals developed ornithischian eating habits and many attained similar size. That phenomenon illustrates the , in which assemblages of vastly different animals can inhabit similar ecological niches. The guild concept is obvious with the many kinds of animals that formed reefs in the past; the , , , , , , , and reefs all had similarities, particularly in their shape and location, but the organisms comprising them, from reef-forming organisms to reef denizens and the apex predators patrolling them, had radical changes during the . If you squinted and blurred your vision, most of those reefs from different periods would appear strikingly similar, but when you focused, the variation in organisms could be astounding. The woodpecker guild is comprised of animals that eat insects living under tree bark. But in Madagascar, where no woodpeckers live, a , with a middle finger that acts as the woodpecker’s bill. In New Guinea, . In the Galapagos Islands, a to acquire those insects. In Australia, , but unlike the others, they have not developed a probing body part, nor do they use tools, but just rip off the bark with the brute force of their beaks.
Cretaceous–Paleogene extinction event - Wikipedia
Further along the evolutionary path, here are two animals (, ) that may be direct ancestors of mammals; one herbivorous and the other carnivorous/insectivorous. They both resembled rats and probably lived in that niche as burrowing, nocturnal feeders. included animals that were probably warm-blooded, had fur, and nursed their young, but laid eggs, like today’s . Nursing one’s offspring is the , but there has been great controversy over just which mammaliaformes are mammals’ direct ancestors and which one can be called the first mammal. According to the most commonly accepted definition of a mammal, the , about , nearly 20 million years after . The after a were small (the ), including the mammalian clade, and until the end-Cretaceous extinction.