When geologists first deduced that the current age had been preceded by wide-spread glaciation across the entire northern hemisphere they erroneously concluded that the glaciation had ended and the earth had entered a new geologic period. Subsequently, they named the period of glaciation the Pleistocene epoch and the current period the Holocene epoch as subdivisions of the Quaternary period. This they initially dated as approx 1.6 million years ago, later modified to 2.6 million years.
An ‘epoch’ is defined as having distinct geologic characteristics that distinguish it from the epoch that precedes and the epoch that follows. Upon further examination, study and understanding, during the 20th century it became evident that the geologic conditions that gave rise to the Pleistocene epoch had not changed.
Those conditions involved primarily two regions of the Cordillera, the southern end where South America and Antarctica were connected and the central gap in the mountains that allowed Pacific water to flow freely into the Atlantic via the Caribbean Sea. The first condition was the insulation of Antarctica when the southern Cordillera subsided allowing the Drake Passage to open between the tip of South America and Antarctica approx 23 million years ago. As the mountains sank deeper, the Drake Passage expanded the distance of open water between the two land masses, an Antarctic circumpolar current became established. The circumpolar current isolated Antarctica, preventing warmer water from equatorial regions reaching the continent. Thus isolated, the continent began to cool. By approx 15 million years ago the continent was essentially totally glaciated. This was the beginning of glaciation but confined to the southern polar region. Prior to the discovery of Antarctica in 1820, this southern glaciation was unknown to science and it was 80 years more before exploration of the continent began.
The second condition was closing the Isthmus of Panama between approx 3.5 to 3 million years ago when the central Cordillera uplifted, first as a series of isolated islands and finally as a solid wall of mountains. The closing of the Isthmus changed the ocean currents of the Atlantic dramatically, cutting off warm equatorial water from the Pacific.
There are multiple hypotheses about how exactly these two conditions resulted in the Pleistocene glaciation of the northern hemisphere. But the stage was set and the northern glaciers appeared.
Nothing has changed geologically: Antarctica is still insulated and the Isthmus is still closed. There is no indication that either situation is going to change any time soon. In addition, geologists have discovered that periodically during the Pleistocene glaciation, brief ice-free or nearly ice-free periods occurred at approx 100-125 k year intervals, each lasting approx 10-15 k years. The last one before the Holocene was the Eemian which lasted from 130 - 115 k years ago. So we know now that the Holocene is not a new epoch at all, just another in a series of periodic glacial minima interspersed between the Pleistocene glacial maxima. It will end.
- I think we’re our own worst enemy for a huge number of generations before any meaningful global cooling will occur. And stuff happens so fast, nowadays… I’d love to see mammoths, though, even by bringing them back via genetic material, if we’ve got any.
