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Ice ages are an important realm of scientific investigation. Humanity’s colossal burning of Earth’s hydrocarbon deposits may well be delaying the ice sheets' return; they have been advancing and retreating in rhythmic fashion for . Today, the current pattern's accepted tipping point has been Earth’s orientation toward the Sun, particularly the , which has a roughly 100,000-year cycle. Although Earth’s orientation is universally considered to be the tipping point variable, it is not the only influence. The ultimate cause has been . about 35 mya due to its position near the South Pole and declining carbon dioxide levels. The current ice age began 2.5 mya and was likely initiated by the , which separated the Atlantic and Pacific oceans and radically altered oceanic currents. Also, . Those factors all contributed to the current ice age.

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Significant Energy Events in Earth's and Life's History as of 2014

One of Peter Ward’s recent hypotheses is that animals that adapted to the changing conditions, particularly when oxygen levels crashed, survived the catastrophes to dominate the post-catastrophic environment. In the late Permian, several therapsid lines developed , which may have been used for respiratory water retention in a world where oxygen levels were crashing. This is a controversial issue, and related to the controversy over when reptiles developed . The therapsid ancestors of mammals, , first appeared about 260 mya, and had many .

c. 4.6 billion years ago (“bya”)

The appeared in the late Carboniferous and looked like a modern lizard. It also had some canine-type teeth. Diapsids, however, were marginal animals in the Permian, as that was the time of synapsid and therapsid dominance. Diapsids would not rise to prominence until the Triassic.

Version 1.2, published May 2015. Version 1.0 published September 2014.
A number of acronyms in this essay are not commonly used and at least one is unique to my work.

, to eventually achieve modern levels, begins

Low-oxygen Mesozoic oceans saw the rise of unusual biomes. In methane seeps in the Mesozoic’s global ocean floor, bivalves and brachiopods formed symbiotic relationships with chemosynthetic organisms that digested methane. All over the world, scientists have been amazed to find rock layers almost entirely comprised of shells of those innovative, low-oxygen surviving shelled animals.

Below is a diagram of two hydrogen atoms before and after reaction, as they bond to form H2.

First large-scale energy users.

The Oligocene ended with a sudden global warming that continued into the (c. 23 to 5.3 mya). The Miocene was also the first epoch of the (c. 23 to 2.6 mya). Although the Miocene was , England had palm trees again, Antarctic ice sheets melted, and oceans rose. The Miocene is also called the Golden Age of Mammals. Scientists still wrestle with why Earth’s temperature increased in the late Oligocene, but there is no doubt that it did. As the has demonstrated, many dynamics impact Earth’s climate, and positive and negative feedbacks can produce dramatic changes. For the several million year warm period, carbon dioxide levels do not appear to have been elevated. That data has been seized on by as evidence that carbon dioxide levels have nothing to do with Earth’s temperature, but climate scientists not rarely think that way. Carbon dioxide is only one greenhouse gas, and . But as clouds demonstrate, water is notoriously ephemeral, constantly evaporating and precipitating, and some land can get a lot (rainforests), and some can get very little (deserts). Icehouse Earth temperatures are more variable than Greenhouse Earth temperatures, particularly during the transitions between states, and an Icehouse Earth atmosphere contains less water vapor than a Greenhouse Earth atmosphere.

Those energy and chemistry concepts should make this essay easier to digest.

Concentrated application of muscle energy.

What seems to explain invader and endemic success with those migrations is what kind of continent the invaders came from, what kind of continent they invaded, and the invasion route. Asia contains large arctic and tropical biomes, unlike any other continent. North America barely reaches the tropics and only a finger of South America reaches high latitudes, and well short of what would be called arctic latitudes in North America. Africa’s biomes were all tropical and near-tropical. The route to was straight across at the same latitude, so the biomes were similar. About the same is true of the route to Africa from Asia. Asian immigrants were not migrating to climates much different from what they left. But the route to North America was via , which was an Arctic route. Primates and other tropical animals could not migrate from Asia to North America via Beringia, and even fauna from temperate climates were not going to make that journey, not in Icehouse Earth conditions. Oligocene North America was geographically protected in ways that Oligocene Europe and Africa were not, and it already had substantial exchanges with Asia before and was a big continent with diverse biomes in its own right. It was not nearly as isolated as Africa, South America, and Australia were.