from the book, "Petrified Lightning"
It had been raining steadily for several days, at times rather hard, and flooding had become quite common. The thick soil on the side of the hill was now supersaturated and beyond its limit of stability. Suddenly, without any warning, the soil gave way and slid rapidly downhill. The thick, soupy, all—encompassing mudflow carried branches, small trees and shrubs, and rocks of many sizes, inundating everything in its path. With a roar it poured down the side of the hill and onto the adjacent floodplain, where it hit with enough force to knock over a stand of trees, burying them in the mud.
Such an event may have happened eons ago. The only certainty is that a small stand of trees was knocked over and killed by a mudflow. Radiometric dating showed that this happened about 260 million years ago. Fifteen mineralized stumps were preserved as fossils that scientists would find in 1992. Presumably the stand was a remnant of a much larger forest of trees. The saplings ranged from 3.5 to 7 inches in diameter; they were a well—known genus of seed fern called Glossopteris. Unlike true ferns, Glossopteris had seeds instead of spores; they were often treelike, and all are now extinct. Throughout the area the scientists found the tongue—shaped imprints of fallen Glossopteris leaves.
Deciduous trees such as Glossopteris are an indicator of a warm climate, as is the absence of frost rings. Growth rings of samples from the collected stumps contained none of the ice—swollen cells or gaps between cells that arise when the growth of a tree is disrupted by a seasonal frost. Scientists have concluded that these trees were rarely, if ever, exposed to temperatures below freezing. This is quite incredible, considering that they were discovered in rocks at an altitude of 7,000 feet on Mount Achernar, in the Trans—Antarctic Mountains. This mountainous area just a few hundred miles from the South Pole, was a floodplain millions of years ago when the plants lived there. Obviously, during the Permian Period 260 million years ago, deciduous trees adapted to a warm climate and grew in abundance in what we know today as Antarctica.
In the early days of geologic research, Glossopteris was an insufferable nuisance to earth scientists. Its fossilized remains were found unexplainably in the rocks of widely separated landmasses that included India, Africa, Antarctica, South America, and Australia. For several decades geologists envisioned sunken land bridges even though they found no geologic evidence to confirm pathways over the immense water barriers.
Glossopteris fossils are surprisingly homogeneous. Twenty species of leaves found in Antarctica are common in the rocks of similar geologic age in India, located north of the equator and half a world away. Seeds, much too large to be windborne, could not have blown across thousands of miles of open sea. Nor could they have floated across vast oceans. So how could a uniform land flora be dispersed throughout a hemisphere? The answer was finally provided by the application of plate tectonics, or continental drift. If the seeds of Glossopteris could not make the five—continent trip, the landmasses themselves had to move. Evidence has confirmed that, during the time these plants grew on five continents, the oceans that now separate them simpy did not exist. In fact these landmasses were joined in a single supercontinent known as Pangaea ("all earth").
The most startling, unlikely environment for Glossopteris is cold, windy, formidable Antarctica. During the Permian, however, Antarctica was positioned quite a distance from the south polar region, and its climate 260 million—240 million years ago was temperate to subtropical.
During the Jurassic Period, about 140 million years ago, Pangaea began to split apart. The landmass that became Antarctica drifted to its present geographic position, and India began the long voyage northward, to eventually collide with and become part of the Asian continent. The still—rising Himalayas and frequent earthquakes are evidence that this collision is still in progress.
Looking at a modern world map, one can easily see how South America would fit into the contours of western Africa. They resemble giant jigsaw puzzle pieces. Geologists have authenticated these connections by correlating the rock types and structures from Brazil into West Africa. They are identical and continuous and contain many other fossils of the same flora and fauna. To complete the puzzle, Antarctica, backed by Australia and with India to the north, fills in the space around the East African border.
Of any place on earth, Antarctica has shown the most dramatic evidence of climatic change. Today no true land animals live there, and only lichens, algae, and puny grasses grow where vertebrate animals used to roam through dense forests. But however strange a tropical Antarctica may seem, a greater challenge to the imagination would be a look at the Sahara Desert during the Ordovician Period about 500 million years ago. As landmasses shuffled for a more comfortable position on the planet, the land now known as the Sahara Desert surrounded the geographic South Pole!
But then, no matter what the temperature, barren wasteland is still barren wasteland.