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 saturated soil gave way and moved rapidly downhill as an all-encompassing mudflow. It flowed as a thick, soupy mud that 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 on to the adjacent floodplain where it hit with enough force to knock over a stand of trees, burying them in the mud.
The above is a description of an event that, according to radiometric dating, happened 260 million years ago. The event was a mudflow that knocked over and killed a small stand of trees. Fifteen mineralized stumps were preserved as fossils that scientists found in 1992. Presumably it was the remnant of a much larger forest of trees that ranged in size from 3.5 to 7 inches in diameter. These were saplings of a common genus of seed fern called Glossopteris. Unlike true ferns, seed ferns had seeds instead of spores; they were often tree-like, 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. Scientists analyzing the growth rings of samples from the stumps found none of the ice-swollen cells or gaps between cells that occur when the growth of a tree is disrupted by a seasonal frost. They concluded that these trees were rarely, if ever, exposed to temperatures below freezing. This is quite incredible, considering that they were discovered in deposits on a land where today freezing temperatures are the norm throughout the year. The fossilized tree stumps were found in rocks at an altitude of 7,000 feet on Mount Achernar, in the Trans-Antarctic Mountains. This area, now mountainous, and just a few hundred miles from the South Pole, was a floodplain millions of years ago when the plants lived there. The obvious conclusions are that 260 million years ago, deciduous trees adapted to a warm climate and grew in abundance in what is known 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 land masses that included India, Africa, Antarctica, South America and Australia. For several decades geologists envisioned sunken land bridges even though there was no geologic evidence to confirm pathways over the immense water barriers between the present land masses.
Glossopteris flora are surprisingly homogeneous even though they occur in the rocks on five scattered continents. Twenty species of leaves found in Antarctica are common in the rocks of similar geologic age in India, now located north of the equator and half a world away. They could not have been blown across thousands of miles of open sea because the seeds were much too large to be windborne, nor could they have floated across vast oceans. So how could a uniform land flora be dispersed throughout a hemisphere? The only simple answer was finally provided by the application of plate tectonics or continental drift. The solution was that, if the seeds of Glossopteris could not make the five-continent trip, the land masses themselves had to move. The evidence confirmed that, during the time that these plants grew on five continents, the oceans that now separate them did not exist. In fact, these land masses were joined in a single supercontinent known as Pangea ("all earth").
The most startling and unlikely environment for Glossopteris was cold, windy, formidable Antarctica. During the Permian however, Antarctica was positioned quite a distance from the South Polar region, and its climate 260-240 million years ago was temperate to sub-tropical. About 140 million years ago, late in the Jurassic Period, Pangea began to split apart. The land mass that became Antarctica drifted to its present geographic position, and India began the long voyage northward, eventually to collide with and become part of the Asian continent. The majestic and 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 like a giant jigsaw puzzle. 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, filled in the space around the east African border.
Through time Antarctica has shown the most dramatic evidence of climatic change of any place on earth.
Today, no true land animals live there, and only lichens, algae and stunted grasses grow where formerly vertebrate animals roamed through dense forests. However contradictory tropical Antarctica may seem, a greater challenge to the imagination would be a look at the Sahara Desert about 500 million years ago.
As land masses 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 wastelands are still barren wastelands.
Phil and Nancy Seff are the authors of several science books, including "Our Fascinating Earth." Their column runs regularly in the Deseret News Science/Technology section.