One hundred million years [100,000,000 years] is a small step in geological time, barely enough for mountains to ‘fold’ or erode, or oceans to open/close. Yet it is possibly too great a time for the human mind to comprehend.
By this measure, modern man evolved a mere instant ago. Even the oldest rocks in Ireland, the schists and gneisses of Donegal and the Sperrins, have been in place for just ten of Earth’s 46 steps (it’s about 140 steps since the Universe began in the Big Bang) and the oldest rocks in our vicinity, the Ordovician and Silurian shales of the Longford-Down Inlier are a mere four/five steps old.
Those familiar mountains that define our human horizons, the Mournes, Cooleys and Gullion emerged to the surface just a half step ago, though they formed as magmetic plutons deep within the earth some four-five steps in time ago. The recent Ice Ages that helped to sculpt our immediate landscape happened one half of one thousandth of a step ago by our measure, and man has occupied these regions for less than one tenth of that miniscule time period. These time spans help to focus our minds.
We know about Earth’s history from our developing theories of Earth’s processes and from the evidence of the geological record. To continue with our time scale analogy, some five steps ago most of earth’s huge tectonic plates were located in the southern hemisphere, the vast Laurentia plate that contained the modern North America as well as what we know now as Greenland, North Ireland, Scotland etc. being separated by 40