Glaciation and Azolla Event

More than 45 million years ago, the presence of stagnant freshwater atop the Arctic Ocean fostered the growth of the fern Azolla. Over the course of hundreds of thousands of years, this plant's growth caused a climate shift that moved the warm Earth into the period known as the Ice Age. This period, which continues to this day, created massive ice sheets (glaciers) that at one point covered much of what is now Asia, northern Europe, and North America. Glaciation has shaped much of the earth's topography, leaving some areas flat and others rocky and mountainous.

Basic Principles

About 49 million years ago, during the middle of what is known as the Eocene epoch, the Ice Age began with the introduction of a new species of fern, Azolla, to the Arctic Ocean. The warm and landlocked Arctic Ocean began to receive fresh rainwater, which set off a process in which the fern's rapid growth caused a chain reaction that reversed the earth's greenhouse effect and ushered in a cold climate highlighted by glaciation.

Glaciers have significantly affected the geodesy (the shape and topography) of the earth, causing the formation of mountain ranges and other features. Glaciers also are the primary source of the planet's freshwater and contribute to the stability of the planet's climate. Glaciers play an important role in the earth's interior processes, triggering volcanic activity and causing the movement of the tectonic plates beneath the earth's crust.

Glaciers were at their thickest and most numerous between about 27,000 and 19,000 years ago, during a period known as the last glacial maximum. However, glaciers still exist at high altitudes, and at the earth's polar regions, indicating that Earth remains in a waning period of the Ice Age.

Background and History

One of the most vexing questions paleontologists and other scientists have attempted to answer concerns the causes of the Ice Age. During this period, which began about 50 million years ago, the earth's climate shifted dramatically from warm to cold, giving rise to glaciation (the creation of massive sheets of ice). At the beginning of the twentieth century, this mystery seemed to be based on scientific curiosity. Scientists now are concerned that a similar climate shift could occur in the near future.

As early as the mid-nineteenth century, scientists began to explore the idea that the regions humans now live on were previously buried under ice sheets (glaciers) several kilometers thick. Soon afterwards, scientists agreed that not only did such glaciations occur, but other periods of major climate change also occurred before the Ice Age. The apparently cyclical patterns of ice ages led scientists to wonder about the causes of such events. Some speculated that these climate shifts could be attributed to extraterrestrial elements, such as the gravitational effects of other planets on the earth or changes in solar activity. Others argued that the climate shifts were caused by Earth's solar orbit: During cycles of about ten thousand years, areas in the Northern Hemisphere would see less sunlight, a phenomenon that caused snow and ice buildup.

The introduction of new technologies greatly aided the pursuit of scientific information about the Ice Age. One critical scientific practice, radiocarbon dating, was introduced in the 1950s, enabling scientists to date paleontological samples to their approximate dates of origin. In time, radiocarbon dating practices continued to improve, with core samples being successfully extracted from higher elevations and the ocean floor, offering much information about these climate shifts.

The Azolla Event

Approximately 49 million years ago, during the early Eocene epoch, the Arctic Ocean was considerably warmer than it is today and was almost completely landlocked. Rain left a great amount of fresh surface water, and the rains also brought with them the nutrients that sustain plant life. Subsequently, a freshwater species of prehistoric fern, Azolla, began to develop in this thin layer of freshwater atop the ocean. Scientists believe that the Azolla, when exposed to optimal environmental conditions, could reproduce rapidly.

During this time in Earth's history, the rains over the Arctic Ocean were cyclical. Paleontologists and botanists believe that the ferns flourished during periods of high rains, such as those during the Eocene summers, and retreated when conditions changed. With the freshwater rainfall came Cyanobacteria, which produce organic nitrogen—a staple for plant life. Fossilized remains of Cyanobacteria located within sediment samples revealed that Cyanobacteria was present in great volumes beneath the Arctic Ocean.

Scientists believe that dead Azolla sank beneath the ocean's surface, and because oxygen at the bottom of the ocean was scarce (a condition known as anoxia), the ferns were immediately fossilized rather than consumed by bacteria. The fossilization of the dead Azolla also resulted in the draw-down (or sequestration) of massive amounts of carbon dioxide from Earth's atmosphere. This led scientists to believe that the fern played a direct role in shifting Earth's climate from a greenhouse environment to an “icehouse” environment.

Glaciation

In time, the Azolla event led to a gradual cooling of the planet. Scientists have been able to uncover evidence of this transition by observing high sea levels that date to the late Paleocene epoch (which preceded the Eocene). Evidence also shows a gradual reduction in sea levels associated with global cooling starting to become manifest in the late Eocene and subsequent early Oligocene epochs. This drop in sea levels was caused by the development of enormous bodies of ice (the glaciers). The largest of these are called ice sheets, massive bodies of ice that could cover continent-sized regions and which began to develop in the eastern regions of the Antarctic during this period.

Throughout the Ice Age, glaciers spread and retreated as temperature cycles fluctuated. At one point, approximately 30,000 years ago, glacial thickness was at its highest for this era (and sea levels were at their lowest), marking the last glacial maximum.

The glaciers that formed during this period of global cooling began to move slowly, pushed by gravity and aided both by the deformation of internal ice crystals within them and by the lubricating effects of melting ice at the surface. When in motion, however, glaciers also have major effects on the surface over which they move, picking up and placing minerals great distances from their points of origin. Additionally, because of the enormous weight of these ice sheets, Earth's crust is pushed downward as they pass. After the glacier moves onward, the previously depressed crust slowly returns to its original shape—a process called postglacial rebound. The modification of the earth's surface caused by these bodies of ice is called glaciation.

The Holocene Epoch

The full effects of the Azolla event and the Ice Age it created have not yet been fully realized. After all, many of the glaciers that were created during the Eocene epoch (most notably the ice sheets of Antarctica and Greenland, as well as glaciers found in higher elevations around the world) still exist. Put simply, the earth remains in an ice age and glaciations are ongoing.

Scientists, however, can study the effects of glaciation from other epochs on the timeline. For example, scientists have learned that, during the Miocene epoch (which followed the Oligocene), a period of relative warming and glacial retreat existed. Studying the North American area, researchers saw evidence of the postglacial rebound that caused the flattening of a number of regions. When the climate began to return to a cooler temperature in the subsequent Pliocene epoch, the glaciation caused during the Miocene enabled the Pliocene glaciers to be much larger and thicker. Glaciologists, climatologists, and geologists use the data obtained from such samples to create models of glacial development and climate change and to develop scenarios for how the current glacial period (the Holocene epoch) will end.

Geological and Mineral Analysis

Evidence of both the Azolla event and the effects of glaciation have been found all over the world. In many cases, such evidence is carried to other parts of the world on icebergs, which broke away from polar ice sheets and carried scientific evidence across the ocean. In such situations, it is often difficult to separate the ice of today from the ice of prehistory. Scientists have been able to do so by looking past sea ice that has become embedded in icebergs and focusing on quartz and other minerals found within the body of the ice. In one study, scientists working on the Lomonosov Ridge (a suboceanic ridge of continental crust in the Artic Ocean) located the presence of quartz in a sample, giving researchers the ability to focus on the segments of ice that came from the middle Eocene epoch rather than sea ice found attached to the iceberg. In another study, scientists analyzed sediment found within the body of an ice raft. Based on a geological and mineralogical analysis of the sediment (which originated in the late Eocene/early Oligocene epochs), the researchers determined that the block had originated in a glacier found in the area of Norway, supporting the notion that the Azolla event caused glacier development in not only what is now the Antarctic but also elsewhere in the world.

Satellite Technology

Because of the sheer size and volume of glaciers, the effects of glaciation are often difficult to assess from a ground-level perspective. For this reason, satellite technology has become an invaluable tool for glaciologists. Satellites can collect an enormous amount of data on a single area as they fly over. Scientists may use satellite data to study the effects of multiple periods of glaciation on a particular region. For example, in the early twenty-first century, researchers utilized the Landsat-7 satellite to observe the effects of glaciation on an area of Siberia, Russia. The Landsat-7 data revealed a number of different eras in which glaciation had occurred, forging riverbeds in some areas and blocking waterways in others. In some regions the terrain had been flattened, while in others steep mountains were formed. These satellite data revealed multiple examples of glaciation from different epochs in Siberia's prehistory.

The Landsat satellite system also has proved useful in the study of the deterioration of glaciers during a period of climate change. In one case, scientists used the satellite's infrared and thermal sensors to study a glacier atop Mount Kenya in Africa. The satellite, compiling enormous volumes of data, provided a thirteen-year analysis of the glacier's slow reduction in volume and of the changes in the region's topography caused by the glacier.

Computer Models

Compiling available data on the Azolla event and glaciation is a difficult process in light of the global distribution of evidence. It is in this area of research that computer models are invaluable tools in the study of these two connected concepts. For example, scientists studying glaciation of the Weichselian ice sheet, which during the last glacial maximum covered most of Scandinavia, used computer models to study the directions of ice flow since that event.

Computer models also can help scientists compare the Azolla event's influence on the Eocene climate with climate change occurring in the present. In one case, researchers created a computer model using chemical and biological data (such as marine fossils and oxygen isotopes) from the Eocene epoch to create a simulation of how the Eocene climate changed during and following the Azolla event. Such a simulation can help scientists look for clues regarding the current climate and changes that may occur in the future.

Relevant Organizations and Networks

The Azolla event and the glaciation that occurred as a result have strong implications for human civilization. Arguably, the most prominent of these implications is the ongoing scientific and political debate surrounding global warming and climate change. A number of organizations and institutions, including the following, play roles in the study of these two concepts.

Governments play important roles in terms of both funding scientific research on glaciation and climate change, and conducting their own research. For example, the U.S. Geological Survey includes a climate and land-use-change program, designed to study (among other issues) the effects of carbon sequestration, a natural and artificial process whereby carbon dioxide is withheld from the atmosphere and instead retained in an idle location, such as within the soil or at the bottom of the ocean. Carbon sequestration was a major contributor to the climate change caused by the Azolla event. By studying that event, governments hope to better understand carbon sequestration's potential effects on the environment.

Universities play a critical part in the study of climate change and glaciation. It is in such institutions that field research data are compiled, computer models generated, and theories about the effects of the Azolla event and subsequent glaciation are presented. Universities also serve as vehicles for public awareness of the significance of these phenomena, educating students and the general public on how to apply what has been learned about the last 50 million years to today's natural world.

The Internet has made possible the widespread work of many scientific societies and networks focused on glaciation and climate change. The International Glaciological Society, for example, provides symposia and conferences in which its members share theories and data. The society also features a publication for scientists to submit their own research.

Implications and Future Prospects

Radiocarbon dating has greatly benefited the study of the Eocene climate shift and the glaciation that resulted from the Azolla event. Technologies such as the Internet, computer modeling, and satellite systems have further enhanced the study of these events and processes. These advanced systems have enabled scientists to research both the prehistoric past and the present and to place any discoveries in this arena within the context of future climate change.

One of the most pressing aspects of the study of the Azolla event and glaciation is that scientists believe there is strong evidence that climate change is again occurring. Scientists look to the carbon sequestration that occurred during the Azolla event as a model for understanding examples of what is believed to be human-made carbon sequestration today. Furthermore, recently proven diminutions in the earth's glaciers and rising sea levels show a similarity to events that followed the early Eocene. Therefore, the Azolla event and the effects of glaciation in the last 50 million years are relevant to understanding what could happen to Earth should the planet's climate continue to warm.

Principal Terms

Azolla: species of prehistoric fern that can reproduce rapidly; believed to be the initial cause of the climate change that led to the Ice Age

carbon sequestration: a natural and artificial process whereby carbon dioxide is withheld from the atmosphere and instead retained in an idle location

geodesy: study of the earth's shape, topography, and physical features and forces

greenhouse effect: environmental phenomenon in which carbon dioxide and other gases are released into the atmosphere; these gases filter the sun's ultraviolet rays and redistribute warmth around the planet

last glacial maximum: prehistoric period, approximately 30,000 years ago, in which the glaciers that covered the earth were at their thickest

plate tectonics: theory stating that beneath the earth's outer crust is a series of plates in constant motion and through which magma flows

postglacial rebound: process by which Earth's crust slowly returns to its original position after a glacier dissipates or moves away from the subduction zone

subduction: geodynamic process whereby an extremely heavy object located on the outer crust pushes down on the crust and the tectonic plates beneath it

Bibliography

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Varanasi, Anuradha. "Could a Tiny Fern Change the World