Mean atmospheric O2
Geologic Time Scale
The Pharos of Alexandria at twilight
The Pharos (lighthouse) of the ancient Egyptian city of Alexandria as it may have appeared 2,000 years ago.
The lighthouse, one of the Seven Wonders of the Ancient World, was commissioned in the 3rd century BC by Ptolemy I and completed 12 years later under the rule of his son Ptolemy II. Built mostly with solid blocks of limestone, it is believed to have been about 400 feet tall (about 40 stories) making it one of the tallest man-made structures for many hundreds of years. It sat on the small island of Pharos near the coast of the Nile Delta's western edge, guiding ships to Alexandria's Great Harbor for nearly 1,500 years.
The Pharos of Alexandria survived several major earthquakes until finally falling into ruin in the 14th century. About 100 years later its limestone was used to construct the Citadel of Qaitbay at the same location.
|* Some experts argue that Holocene ("entirely new") should be replaced with the term “Anthropocene” ("man new") because humans have caused mass extinctions of plant and animal species, while distributing others across the globe, polluted the oceans, and altered the atmosphere.|
Copyright © Walter B. Myers. All rights reserved.
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