The holocene always struck me as odd. Here we have the final geologic epoch, and it's 10,000 years old, and every other geologic epoch is ~50M years long. And it just happens to coincide with the rise of our species, who just happens to be the one creating the taxonomy.<p>Paleohistory is pretty fascinating, and it's easy to forget just how small we are on this big earth and how much things differ from today. For example:<p>We're technically in an icehouse age. An icehouse age is defined as "any period of time where glaciers exist <i>anywhere</i> on the planet". For about 80% of geologic time, there is no such thing as a glacier, or of snow and ice for that matter. The entire earth's surface is above freezing, even the North and South poles. What we know of as an "ice age" (a glaciation) is a feature only of icehouse states. We currently happen to be in an interglacial of an icehouse age, which is why we think of this as being a warm period. But geologically, the earth is <i>well</i> below its temperature average.<p><a href="https://en.wikipedia.org/wiki/Greenhouse_and_icehouse_Earth" rel="nofollow">https://en.wikipedia.org/wiki/Greenhouse_and_icehouse_Earth</a><p>It's likely that the earth has completely frozen over on at least two occasions, with the entire planet being encased in a gigantic ice sheet like Europa:<p><a href="https://en.wikipedia.org/wiki/Snowball_Earth" rel="nofollow">https://en.wikipedia.org/wiki/Snowball_Earth</a><p>The larger of these two incidents may have been triggered by the evolution of photosynthesis and the addition of oxygen into the earth's atmosphere, which also likely caused a major mass extinction among the dominant anaerobic bacteria of the time:<p><a href="https://en.wikipedia.org/wiki/Great_Oxidation_Event" rel="nofollow">https://en.wikipedia.org/wiki/Great_Oxidation_Event</a><p>Sea level over time has fluctuated by 300-400 meters. That means that anything at an altitude of less than about 1000 feet (which is the vast majority of human settlements) was once underwater. (Well, technically <i>land</i> level fluctuates more than sea level, so most of these low-lying areas are actually sediment weathered off of nearby mountains.)<p><a href="https://en.wikipedia.org/wiki/Past_sea_level" rel="nofollow">https://en.wikipedia.org/wiki/Past_sea_level</a><p>There've been some massive outburst floods in the past, like the draining of Glacial Lake Missoula (a pleistocene lake roughly half the volume of Lake Michigan, held in by an ice dam on the Clark River nearly 2000 feet tall) which released an outflow 13 times the size of the Amazon River:<p><a href="https://en.wikipedia.org/wiki/Missoula_Floods" rel="nofollow">https://en.wikipedia.org/wiki/Missoula_Floods</a>