Glossopteris and the moving continents

Featured Image: The supercontinent Pangaea. Illustration by Gillis Björk.

INTRODUCTION

The early 20th century was a period of profound scientific discovery and innovation. Einstein had published his theory of special relativity in 1905 while working for a patent office; Rutherford created the first model of the atomic nucleus in 1911, and in 1912, a little-known meteorologist made his debut into geology by proposing his theory of plate tectonics, making the seemingly preposterous claim that the Earth’s continents moved. But it was also the last real era of exploration. The colonial era of centuries prior had fostered explorers that journeyed to the far reaches of the Earth until only the most inaccessible areas were left: the poles. During the scientific revolution and global war that followed, an unassuming genus of extinct plants called Glossopteris came to prominence and helped drastically change the way we viewed the world, both in the present and far back into the past.

THE DOOMED EXPEDITION OF THE TERRA NOVA

On June 15, 1910, Captain Robert Falcon Scott stepped on board the Terra Nova and set sail from Cardiff, Wales, headed for Antarctica. The object of the expedition was mainly scientific; on board were researchers from several disciplines, including biology, geology, meteorology, and physics. But Captain Scott was an Englishmen, and along with the goal of scientific discovery, he wanted to give England the honor of having supported the first expedition to reach the south pole.

The crew sailed from Wales to Australia and New Zealand to further prepare and gather supplies, but during one of their stops, Scott received a telegram informing him that the Norwegian Roald Amundsen had just set sail for Antarctica. Amundsen was a renowned explorer at the time, known for his meticulous planning. Aware of Scott’s intention to reach the southern pole, Amundsen set sail without any encumbering scientific equipment or personnel with only one goal in mind: to circumvent Scott and be the first to reach the pole, winning the glory for Norway.

The Terra Nova

Still, Scott remained undaunted and refused to sacrifice any of the scientific lines of inquiry in his bid for the pole. They reached Ross Island on January 4th and proceeded to set up camps further inland. Parties were sent out over the next several months to explore and make scientific observations, including an expedition to collect Emperor Penguin eggs from the nearest colony, some 70 miles away. Emperor penguins only lay their eggs in June, so the party was forced to set out amid relentless blizzards, temperatures well below -50°C, and the perennial darkness of an Antarctic winter.

The expedition to the pole, a 900-mile trek one way, would wait until Spring when the weather had cleared and in time for food depots to be established along the route to ensure sufficient provisions for the long journey. But the ponies they used to cart the food stores weren’t up to the weather, and Scott decided to set up the final and largest food depot 30 miles north of where he initially intended to place it, a decision that would come back to haunt him.

The party left on November 1st, 1911, and the final four men Scott choose to accompany him to the end consisted of Henry Bowers, Edgar Evans, Lawrence Oates, and Dr. Edward Wilson. They reached the pole on January 17, 1912, only to find that Amundsen had already beaten them to it and erected a black flag above the ice. They had been preempted by only a month. But the loss of the pole was only the beginning of their troubles.

Members of the doomed Terra Nova Arctic trek. From the left: Captain Scott, Edward Wilson, Henry Bowers, Lawrence Oates, and Edgar Evans. Recuerdos de Pandora

Disheartened and low on food, they began their return journey north. Some of the men fell into crevasses (a common occurrence on the expedition) and had to be pulled out, and a few began to show signs of frostbite, which gradually became more and more severe. Worse still, Evans, normally hale and full of spirit, became seriously ill. The party was barely making it to each food depot without running out of supplies in between.

After reaching one such food-stop, their spirits a little lifted, the team made a slight scientific excursion under the welcoming shelter of a moraine beneath Mount Buckley. There they made camp and spent a few pleasant hours collecting geologic samples in the vicinity. It was here that the men cut away portions of sandstone bearing fossils of ancient plants, among them specimens of the extinct gymnospermous plant Glossopteris. The fossils added 35 lbs. to their already heavy packs, but after the devastating defeat at the pole, it doubtless felt good to take part in the real reason they’d come to the lifeless continent: to discover. In so doing, the team demonstrated that the Antarctic hadn’t always been so lifeless after all and had instead once supported a lush, temperate forest. This singular discovery would later aid in the development of the biggest and most controversial geologic theory of the 20th century.

But for Scott’s party, this was to be the last pleasurable moment of the expedition. Not long after, Evan’s condition rapidly worsened. At one point on their trek, he fainted in the snow and later that night died quietly in his tent. From there a fine mesh of ice slush hindered their progress, followed by blizzards and steadily decreasing temperatures as winter approached. Oates’s health was the next to decline. Knowing that he was delaying the progress of his friends, he walked out of his tent one morning either on his birthday or the day before and trudged off into a blizzard. His body was never found.

Scott, Wilson, and Bowers were now the only members left of the initial expedition, and they could no longer maintain any delusions about their plight. Though they spoke optimistically, it was at this time that Scott began writing his farewell letters. They left behind equipment to lighten their load, but Wilson requested they keep the 35 lbs. of fossils.

On March 19, after having struggled for two months to reach the coast, a blizzard struck, and the trio were forced to shelter in their tent. The blizzard raged on, unrelenting, until it was too late.  All three men died together, and their tent was buried in the snow. They were just eleven miles from the last food depot, the one which Scott had placed thirty miles north of its intended destination. It would be another seven months before a search party would stumble across the tip of their tent protruding from the snow and their bodies and journals recovered.

THE CONTINENTS MOVE

 It was Christmas day of 1910, while Captain Scott was aboard the Terra Nova ten days out from Antarctica, that a man named Alfred Wegener sat with a friend and flipped through the pages of a world atlas, his friend’s Christmas gift that year. Wegener later wrote, “While we were doing so, an idea occurred to me…Doesn’t the East Coast of South America fit exactly into the West Coast of Africa, as if they had formerly been continuous? …I’m going to have to pursue this.”

Wegener (pronounced Vegener) was an avid arctic explorer in his own right, taking part in four expeditions to Greenland. Born in Berlin in 1880, he led an eclectic academic and adventurous life. He received a PhD in astronomy at the age of 24, which he immediately abandoned in favor of a meteorological position where he worked with his brother sending out weather balloons and kites to monitor atmospheric conditions. Together, they set the record for the longest balloon flight of 52 and ½ hours. It was this work that provided the stepping stone for his appointment as chief meteorologist in a two-year expedition to Greenland. At the time of his eureka moment on Christmas, he was serving as a lecturer at the University of Marburg.

During the next five years, he gathered available evidence, which led him to an unmistakable conclusion: the continents moved. They were not giants at rest, but dynamic plates that pushed, pulled, subsumed, and fractured. They threw up mountains like dust upon colliding and hollowed out abyssal rifts where they came apart. But World War I slowed the development of his ideas, in which he served as a low-ranking officer on the side of the Germans. But after being wounded twice on the Western Front, he took leave at home to recover and used that time to write the book ‘On the Origin of Continents and Oceans’ in which he describes the mounds of evidence he had accumulated supporting his theory of plate tectonics.

Alfred Wegener

The fossil record played an important role in his thesis. Layers of coal found in India, South Africa, Australia, and South America contained many of the same plants, the most prominent being Glossopteris. And thanks to Captain Scott’s expedition, it was then known that Glossopteris once grew in Antarctica as well. Because of the relatively large size of Glossopteris seeds, it was virtually impossible that they had been dispersed by wind halfway around the world. Earth’s landmasses must have at one time been joined together. Wegener named this supercontinent Pangaea.

Range of various organisms in the Permian; Glossopteris highlighted in green.

Today, plate tectonics is the foundational science of geology, but Wegener’s theory wasn’t accepted by the scientific community during his lifetime. He was an outsider to the field, a meteorologist who had no business meddling in geology, and if correct, his theory would change everything geologists thought they knew about the world. It also didn’t help that World War I had stirred up anti-German sentiment in the West.

Wegener submitted revised versions of his book throughout much of the rest of his life, but it did little to detract from the short-sightedness of his critics. On April 1st, 1930, Wegener set sail on his fourth and final arctic expedition to Greenland. After successfully completing a re-supply mission to an isolated camp, he and his companion headed off to a station where they intended to wait out the winter. But on the way, Wegener suffered a severe heart attack and died in the cold arctic north; he had just celebrated his 50th birthday two weeks prior. His companion buried him in the snow and then himself disappeared. No one ever ascertained his fate.

Alfred Wegener (left) with Rasmus Villumsen (the man who buried him) about two weeks before the former’s death.

THE GREAT DYING

With the exception of what was then the small island of China, Earth’s landmasses had sutured to form Pangaea by the end of the Permian, 251 million years ago. The end Permian is also marked by the greatest extinction event of all life on Earth, known as the Great Dying. Approximately 80-90% of all marine species went extinct, with some groups disappearing entirely. Plants and animals on land fared only slightly better, with a conservative estimate of 63% total extinction. But unlike the asteroid impact that killed the dinosaurs, the cause of the Permian extinction has been much harder to pin down, and there are currently several theories as to why it occurred.

Glossopteris went extinct during this time as well, and just as its diversification and distribution helped Wegener formulate his theory of plate tectonics and predict the existence of Pangaea, the waning of Glossopteris ecosystems and their eventual demise has also helped researchers better understand the underlying mechanisms behind the Permian Extinction.

The genus Glossopteris contained temperate, deciduous trees. The trees lost their leaves in the fall, indicating cold winters, and the trunks had observable growth rings, indicating distinct warm and cold seasons, unlike species in the continually warm tropics at the time, which had no growth rings. Taken together, this suggests that the southern portion of Pangaea during the Permian had a similar climate to the present day Northeast United States. But by the end of the Permian, Glossopteris rapidly disappeared from the ecosystems it previously dominated and was replaced by the genus Dicroidium, a group of plants that was adapted to hot, dry conditions, indicating rapid climate change occurred during that time.

Glossopteris reconstruction

While there’s no single consensus as to what caused the Permian Extinctions, the current evidence suggests that a number of interactive environmental disasters occurred that caused a feedback loop, in which climate change spiraled out of control. Siberia was slowly drifting over a thin portion of Earth’s mantle through which Earth’s core had burned a giant hole, releasing an expanding plume of melted rock just beneath the surface. Mantle plumes don’t erupt through the types of volcanoes common at fault lines, however; instead, it slowly burned through the surface in the form of molten basalt, covering 1 million sq miles of Siberia with magma that was in some places over a mile deep. The eruptions continued for just under a million years, spewing ash, CO2, and methane into the atmosphere.

The massive amounts of greenhouse gasses released caused the world to warm, which in turn caused huge stores of methane at the bottom of the world’s oceans to percolate and enter the atmosphere as well. The more temperatures rose, the more methane was released. Researchers estimate that global temperatures climbed by 6°C at the end of the Permian. To put that into perspective, climate scientists warn that 4°C is presently the tipping point beyond which climate change is irreversible. While this sudden global warming drastically changed terrestrial ecosystems and led to the extinction of plants and animals on land, it’s also likely that it reduced ocean circulation around the world, reducing the amount of dissolved oxygen in benthic environments and causing massive extinctions in the seas.

 

FURTHER READING

Greene, M. T. (2015). Alfred Wegener: science, exploration, and the theory of continental drift. Baltimore: Johns Hopkins University Press.

Preston, D. (1998). A first rate tragedy: Robert Falcon Scott and the race to the South Pole. Boston: Houghton Mifflin.

Stanley, S. M., & Luczaj, J. A. (2015). Earth system history. New York, NY: Freeman/Macmillan Higher Education.

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