Ends of the Earth: Journeys to the Polar Regions in Search of Life, the Cosmos, and Our Future

by Neil Shubin

On November 1, 1911, Scott’s team of five men set off on the trek. Amundsen had launched his attempt with a sledging team of four Norwegians two weeks earlier. When Scott’s team ultimately arrived at the South Pole on January 17, 1912, they were despondent to find a tent with a Norwegian flag extending from it, as well as a note from Amundsen to Scott.

Their precious haul was a collection of fossils of a plant known as Glossopteris, a species that lived about 300 million years ago. While southern beech, fossilized in lumps of coal, was not part of the collection on the sledge, its presence was recorded in Wilson’s diary. Similar fossils discovered since that expedition have been dated to be 5 to 7 million years old. The key point is this: Glossopteris is a tropical plant, and the southern beech is a temperate one. Neither species was ever thought to be polar. Wilson’s ancient plants lie about 100 miles from the South Pole—a place devoid of plant life today.

Edward Wilson, part of Robert Falcon Scott’s last expedition ending in all of them dying.

Some of the most famous glacial marks lie inside Central Park in Manhattan. Sheep Meadow, just north of the famous Central Park Carousel, has dark schists whose deeply carved surfaces are visible today; these grooves were made as the glaciers retreated from Manhattan 12,000 years ago.

The tectonic plates that cover the Earth’s surface have been moving over eons of time, so much so that plates that were once close to the equator now sit at the poles.

Cartographers of the distant past deploy an arsenal of tools to estimate the age and geographic coordinates of rock formations. For age, the best methods involve the “atomic clocks” inside mineral grains. Certain atoms decay into others at known rates, and these rates can be used to estimate the ages of rocks and geological layers with varying degrees of precision.

To determine ancient latitudes from these samples, geologists measure the tilt of the iron fragments in the rock. The steeper the tilt, the closer the sample formed to the ancient magnetic pole, and thus, the higher the latitude. To determine ancient longitudes, scientists measure the angle of the iron fragments to geographic north.

Large ice sheets did not exist during the first 2 billion years of Earth’s 4.56-billion-year history. While ice might have sat on isolated mountaintops, the poles, along with the rest of the planet, were virtually ice-free.

710 million years ago, glaciers extended from the poles to the equator; land was covered by glaciers while the surface of the oceans was frozen solid. Our blue planet was once an entirely white one.

Paul F. Hoffman, now retired from Harvard University.

In 1992, Joseph Kirschvink at Caltech developed the hypothesis of a frozen “Snowball Earth” and made specific predictions of what could be found in the geological record. The idea was overlooked because he published it as a seven-paragraph paper in a 1,348-page book. Working only few years later, Hoffman and his colleagues assembled the data to confirm the hypothesis conclusively.

There was an interval when the entire planet was as cold and icy as the poles are today.

there was not just a single period when our planet turned into an ice ball, 710 million years ago; there was another one 50 million years later. And each frozen interval lasted about 10 million years. Each time the Snowball Earth thawed, the world immediately flipped to one with no ice at the poles or anywhere else.

About 460 million years ago and again 260 million years ago, periods of intense cold set in for about 20 million years. At these times the only ice was located at the South Pole, while the northern polar region lacked glaciers altogether. After these cool periods, the Earth returned to being a warm place. The ages when dinosaurs, mammals, and birds arose were warm times.

Around 55 million years ago, the world’s temperatures rose to between 81 and 94 degrees Fahrenheit for 170,000 years. While that period was unusually hot (keep in mind that the average global mean temperature for the twentieth century was 57 degrees), it has become a case study on what happens to the planet during intense global warming.

Polar ice caps have only been a feature of our planet for roughly 10 percent of its existence. Our perception of what is geographically “normal” is skewed by the fact that the entire history of our species happened during a special time on planet Earth—one with ice at both poles. For most of Earth’s history, despite relati...

This ledge later became known as the Dinosaur Dance Floor for the hundreds of tracks of large and small dinosaurs that crisscrossed each other. Some 200 million years ago, this site sat at the margin of a large lake and dinosaurs etched the mud with their feet as they ran.

. . . a fellow graduate student, Steve Gatesy, and me on a trek to the coast in search of fossil bones. This was the second summer of the Greenland project, in 1989. . .

the rocks in these different regions share more than dinosaur footprints. Versions of the same green and red sandstones extend from eastern North America to Greenland too. These types of rocks and footprints are also found in Morocco, Algeria, and parts of western Europe. Two hundred million years ago, dinosaurs could have walked from what today is Greenland to Massachusetts and on to Morocco and Algeria without ever hitting ocean. The land was connected in a giant continent given the famously epic name—Supercontinent Pangea. The rocks in Greenland were deposited as the supercontinent drifted and as North America separated from Africa and Europe, forming the Atlantic Ocean.

. . . Grallator trackways have been found in Nova Scotia, Connecticut, and Pennsylvania and south along the eastern seaboard to Virginia and North Carolina. “Dinosaur Dance Floor” in Greenland has same species as these locations.

Urey and Ébelmen surmised that, over long time scales, carbon in the atmosphere sits at a balance between the planetary events that produce it and others that remove it—sources and sinks.

Imagine a world without humans, the one that existed for almost the entire 4.56 billion years of the planet’s history. What was the main the source for carbon in the atmosphere? Today, the immediate source for much of the carbon in the air is human activity, such auto and aircraft emissions, manufacturing processes, and agricultural practices that release carbon dioxide and other greenhouse gases.

We know from estimates derived from current activity that volcanoes can emit almost 300 million metric tons of carbon dioxide every year. While that number is dwarfed by emissions from human activity today, which produce as much as forty times more carbon, over millions of years of geological time volcanoes can pump out an enormous amount of greenhouse gases into the atmosphere.

Some recent estimates suggest that it takes 100 million years for one carbon atom to cycle from the interior of the Earth to the atmosphere to the oceans and back to the interior.

It naturally gets ejected from the interior of the earth from volcanic activity.

More volcanism means more carbon in the atmosphere and warmer climates. Likewise, any mechanism that serves to change how rocks chemically erode can reduce carbon in the atmosphere and reduce global temperatures. The breakdown of rocks does more than explain why we have canyons, valleys, and ocean cliffs—this weathering changes Earth’s climate over long time scales. Anything that accelerates the chemical breakdown of rocks over long periods of time—changes in the amount of precipitation, the position of the Earth’s continents, or the topography of the land—can cool the planet.

If interactions among volcanic emissions, acid rain, and rock weathering control climate, then there should be links between these geological events and global temperatures in the distant past. In 1983, a trio of scientists from Yale, the University of Florida, and Penn State tried to test that idea. Robert Berner, Antonio Lasaga, and Robert Garrels looked at the geological proxies for volcanic activity, acid rain, rock weathering, and other parts of the long-term carbon cycle in the rock record from 500 million years ago to the present.

The team found that, to a rough approximation, they could derive Earth’s temperatures over large time scales by knowing the rates of the geological processes envisioned by Urey and Ébelmen.

In 1983, a trio of scientists from Yale, the University of Florida, and Penn State tried to test that idea. Robert Berner, Antonio Lasaga, and Robert Garrels. . .

Ébelmen and Urey theorized that rocks, the atmosphere, and oceans were linked by the movement of carbon through them. It’s hard to overestimate how ahead of its time Ébelmen’s idea was in 1846: there was little understanding of the age of the Earth, nothing was known of how rocks weather, and his understanding of the carbon content of volcanic gases was guesswork. The world simply wasn’t ready for his idea. It would have been as if somebody had sketched a design for a smartphone in the 1800s—lacking any context, the idea would languish.

To get to the bottom of complex criminal cases, we often hear that it’s best to “follow the money.” To understand the causes of warm and cold periods during the history of the Earth, the parallel is to “follow the carbon.”

If you took a time machine to the early Earth, you’d find there are moments when you’d need a parka at the equator and others when a swimsuit would be useful at the poles.

Sixty million years ago, India sat below the equator as a separate island continent surrounded by water. By about 50 million years ago, it was moving north at the rate of 1 centimeter per year. Over millions of years, India crept ever northward until it slammed into Asia. Still pushing north, the crust at the border of India and Asia was the same density and had nowhere to go but up. Thus began the uplift that formed the Tibetan Plateau. Gradually, this slow uplift led to the origin of the highest mountain range, and the most extensive mountain plateau, on Earth. Today, the Tibetan Plateau continues to rise at about 1 centimeter per year. But erosion of the rocks happens so fast on the Himalayan mountains that their height rises somewhat less—as the mountains get pushed upward, their summits weather downward.

Raymo proposed that the rise of the Tibetan Plateau expanded the amount of rock to be weathered by acid rain. And since weathering causes a drop in carbon in the atmosphere, the entire Earth would have entered a period of slow cooling as the Tibetan Plateau rose.

Maureen Raymo.

Recall that 200 million years ago, all continents were joined as the single supercontinent, Pangea. The supercontinent initially broke up into two pieces: a northern landmass containing what is today Europe and North America and a southern one, Gondwana. The later breakup of Gondwana involved the separation of Antarctica from the other southern landmasses: Africa, South America, and India. As those continents separated 34 million years ago, they left Antarctica at the South Pole while they headed north. As they broke away, Antarctica became encircled by water. This water helped freeze the continent.

The circumpolar current, driven by continual westerly winds, flows around Antarctica clockwise if seen from the South Pole. No land obstructs the flow of water and wind as they circle the globe. With no barriers to slow or otherwise interfere with it, the current has become the most powerful on Earth.

A major mechanism for this current is the difference in salinity between the Atlantic and Pacific Oceans: the saltier the Atlantic is than the Pacific Ocean, the faster the Gulf Stream flows. Saltier waters are denser and descend more powerfully than less saline ones. This effect serves as an engine that drives the Gulf Stream.

In 1941, Serbian mathematician Milutin Milanković hypothesized that regular changes in Earth’s orbit can flip the planet from an ice age to a warmer one. As Earth orbits the sun, it interacts with the gravitational pull of other planets. Saturn and Jupiter exert the greatest effect on Earth’s orbit because their enormous mass dwarfs that of other nearby planets.

The annual traverse around the sun shifts from being shaped like an ellipse to being more circular every 100,000 years. The axis of rotation of the planet swings every 41,000 years while the Earth wobbles like a top in a cycle that lasts 26,000 years. Milanković proposed that these changes conspire to affect the duration of the seasons and the amount of solar radiation that lands on Earth.

For decades these ideas sat as ingenious quantitative calculations lacking any real data. Then, in the 1960s, scientists looked at indicators of past climate changes in the seafloor and found that ice ages have come and gone over the past 3 million years with the regularity of a metronome that is largely calibrated to the orbital cycles Milanković predicted.

The sky deck of the Willis Tower in Chicago stands 1,500 feet over the city’s streets and is home to a panoramic vista that extends for miles over Lake Michigan to the east and the farmland of Illinois to the west. While the glass floor of the viewing station can induce a dizzying swoon, the history of the area is even more vertiginous. Some 26,000 years ago this deck would have sat 1,500 feet below the surface of an ice sheet that extended along the northern United States through the entirety of Canada. The highest skyscrapers in Manhattan would have been encased in ice every bit as much as those in Chicago. Other glaciers up to 3,000 feet thick extended over Europe and across Asia. During this time, the climate was dry, cold, and harsh. So much water was held by massive continents of ice that sea levels were 420 feet lower than they are today.

As glaciers expanded and contracted over Europe and Asia during the ice ages, the populations of Homo heidelbergensis that had migrated out of Africa developed new technologies. One of them, fire, changed the way they lived, ate, and spent time together. They built temporary dwellings and hunted large animals with wooden spears. And, during glacial periods, they retreated into refuges as smaller groups. Over time, this isolation led to increasing anatomical diversity. Populations of Homo heidelbergensis started to look different from one another and a new kind of robust human species appeared by 400,000 years ago: Homo neanderthalensis, or Neanderthals.

The most recent ice age, which witnessed a peak of ice 26,000 years ago, changed sea levels, giving our ancestors new pathways to disperse across the globe and enabling them to migrate from Asia to North America over the Bering Land Bridge.

The ground was shifting for research—the Marshall Plan funds that the United States provided Denmark to rebuild after the war helped the nation purchase new scientific infrastructure.

a mass spectrometer, a new device that could measure the atomic composition of different substances.

In thinking about ice, mass spectrometers, and polar regions, Dansgaard hatched an idea. He knew that the element oxygen existed in two major atomic forms—a heavy one, known as 18O, and a lighter one called 16O.

Higher temperatures provide more energy to move the lighter form of oxygen from water to vapor, and lower temperatures mean more of the heavy form of oxygen stays in liquid. This was bold thinking—if Dansgaard was correct, then the ratios of the heavy and light forms of oxygen in water might serve as a thermometer to indicate ancient temperatures in a sample of liquid water or ice.

Willi Dansgaard was born in 1922 and trained in physics at the University of Copenhagen.

Dansgaard had a new mission. His technique meant that he could measure ancient temperatures in water by looking at ice. This realization meant he could now explore the climate history of the polar north.

In 1964, Dansgaard was able to analyze a section of glacial ice that extended roughly 4,560 feet, representing 100,000 years of time. Dansgaard couldn’t have hoped for more—the core was from the time when glaciers covered Europe, Asia, and North America to when those glaciers melted and receded, starting 15,000 years ago.

the different wind patterns in fall and winter are reflected in the amounts of dust in the ice core.

thousands of years ago, icebergs broke off of glaciers in Canada, rafted into the ocean, and deposited rocky debris that settled to the ocean floor as they melted. Heinrich envisioned that this armada of icebergs was set in motion by the breakup of glaciers. The more scientists analyzed ice cores and the seafloor, the stranger these iceberg-glacier breakup events became. The glacial breakups, involving the separation of hundreds of large icebergs from an ice sheet in northern Canada, happened over the course of less than 250 years. And just as rapidly, each one of these events elevated global sea levels between 3 and 6 feet.

John H. Mercer trained as a glaciologist and held various research positions across the globe. His life changed dramatically in 1960 when he joined Ohio State University’s renowned Byrd Polar and Climate Research Center. Founded by an endowment provided by Admiral Richard Byrd, it became a major center of research on polar glaciers, with scientific luminaries teaching or training there.

The ice of West Antarctica is nearly one and a half miles deep in places. It has a surface area about the size of Alaska and holds 7.2 million cubic miles of ice. If that ice melted and entered the ocean, sea levels would rise about 14 feet worldwide.

to see whether sea levels had been any different 120,000 years ago. Some of the sites with the best sediments to address this question lay in the Pacific. Stands of rocks containing fossils of marine organisms found along the coasts in Indonesia suggested that the sea levels at this time were almost 14 feet higher than they are today.

To Mercer, the connection to Antarctica was inescapable: the amount of sea-level rise as measured in Indonesia matched the volume of water that would be added if the West Antarctic Ice Sheet melted completely and entered the sea.

John H. Mercer trained as a glaciologist and held various research positions across the globe. His life changed dramatically in 1960 when he joined Ohio State University’s renowned Byrd Polar and Climate Research Center. Founded by an endowment provided by Admiral Richard Byrd, it became a major center of research on polar glaciers, with scientific luminaries teaching or training there.

If ice shelves behave, as Mercer and his colleagues envisioned, like dams that hold back glaciers on land from entering the sea, then their disappearance could cause much more ice to enter the ocean. If one the size of a large city can break up in a matter of days, then the floodgates could open for an enormous amount of continental ice to slide into the sea.