Great Ice Barrier, Antarctica, 66° 40′ S, 78° 22′ E to Melbourne, Australia, 37° 45′ S, 144° 58′ E

On December 16, 1957, the Soviet Union set up the Vostok Ice Station on the precise position of the geomagnetic South Pole at the center of the massive East Antarctic ice sheet, as part of their contribution to the International Geophysical Year. It was an ambitious location for a permanently manned station, because Vostok routinely records the coldest temperatures on Earth (the coldest temperature ever recorded, a mind-numbing −89.2°C [−129°F] was measured there on July 21, 1983). In the early days of the station there was no air support to lift in supplies but twice a year a great train of snow wagons made its way up from the coast. By the 1970s, however, Vostok was being regularly supplied by airlift and it was at about this time that the station started doing the experiments for which it is most notable today: taking ice cores to exploit the stratification noticed by Henry Moseley.

The first cores were relatively short, typically less than a kilometer, and were aimed principally at measuring temperature variations over the past few glacial-interglacial cycles, if the strata that represented these cycles could be reached. The Vostok team’s technique for measuring temperatures was a variant of the oxygen-isotope technique that we encountered earlier, with the important

difference that it was the frozen water of the ice itself that yielded the temperature measurement rather than ocean-dwelling plankton. The Soviets measured the oxygen-isotope composition of the water directly and, like Emiliani before them, were able to recognize the transition from glacial to interglacial climates. However, they were looking not so much at temperature as at changes in ice volume as a measure of glacial-interglacial cyclicity. Remember that as ice sheets grow they incorporate proportionally more of the light isotope of oxygen, oxygen-16, because precipitation originating in the low latitudes is enriched in this isotope. Thus, in the same way that glacial intervals can be recognized in the deep ocean (even in the absence of the temperature effect exploited by Emiliani) by a preponderance of the remaining heavy isotope of oxygen (oxygen-18), glacial intervals can be recognized directly in the ice sheets themselves by a preponderance of oxygen-16. Furthermore, the Vostok team used the enrichment of the heavy stable isotope of hydrogen (deuterium) as a crosscheck. In Antarctica a cooling of one degree Celsius results in a decrease of 9 parts per thousand in the abundance of deuterium, an easily measurable amount.

Using these two techniques, the Vostok team soon discovered that ice representing the last glacial maximum, some 18,000 years before present, occurred at a depth of only about 400 meters. Given that they were retrieving cores at least a kilometer long, this could only mean that the rate at which ice accumulated on Antarctica was very slow compared to other locations, such as Greenland. The prospect of retrieving a complete glacial-interglacial-glacial cycle suddenly looked very good. This was the impetus for even deeper drilling, and by 1998 a core 3,100 meters long had been recovered. It was 50 meters longer than anything recovered from either the Arctic or the Antarctic before, reaching back a staggering 420,000 years and easily covering the last four glacial-interglacial cycles.

But it turned out that much more could be done with the Vostok ice cores. Moseley had noticed that the color of the ice layers varied between white and blue and had understood that the

color variations indicated the number and size of air cells in the ice. It was the contents of these air cells that intrigued the Vostok team, because they realized that they contained samples of ancient atmosphere, air samples from the height of the last glaciation as well as from the last interglacial. This approach had recently been pioneered on Greenland ice, but only as far as the end of the last glaciation. The Vostok ice core let scientists examine directly changes in the concentration of atmospheric carbon dioxide, as well as changes in other greenhouse gases such as methane, over several complete glacial-interglacial cycles.

The Vostok team found a close correlation between the concentration of these greenhouse gases and temperature change (measured using oxygen and hydrogen isotopes in the same core), thereby confirming the findings from Greenland that both carbon dioxide and methane concentrations were lower during glaciations than in interglacials. However, the enormously detailed record available from the Vostok core allowed the relative timing of changes in greenhouse-gas concentration and temperature change to be addressed, too. The team found that the transitions from glaciations to interglacials were marked by an increase in greenhouse-gas concentration that preceded the increase in temperature, but during the transition from interglacials to glacials change in greenhouse-gas concentration significantly lagged behind the onset of cooling. The inescapable conclusion was that changes in greenhouse-gas concentration were important in warming the earth out of glacial periods but the interplay of factors that drove the world into glacial phases was more complex.

The Vostok ice core and the other cores drilled in the Antarctic and elsewhere (in Greenland and the Arctic, particularly) eventually yielded much more information than merely temperature and greenhouse-gas change. Variations in the density of windblown dust told how atmospheric wind circulation varied over the past several thousand years, while variations in the concentration of sulfur yielded vital information about the frequency and severity of

volcanic eruptions even thousands of miles away. Seventy-three thousand years ago the Indonesian volcano, Toba, erupted with such force that 600 cubic miles of ash were ejected into the atmosphere. The imprint of this event is writ large in the record of the ice sheets, particularly the Greenland ice core known as GISP-2. Based on evidence from this core, it seems the Toba eruption was the most severe of the past half million years. Short-term shifts in climate can be measured in ice cores if the ice accumulation rate is high enough to resolve the events. (The Vostok-core accumulation rate was relatively low, which is why such a long record was retrievable.) Cores from Greenland, again using subtle variations in the abundance of deuterium and oxygen isotopes, show that there was an abrupt global cooling of about 15°C 12,000 years ago that returned the world virtually to the glacial conditions that gripped the world 6,000 years before that. Astonishingly, this climatic shift, known as the Younger Dryas, is estimated to have occurred over only 5 years but then lasted a staggering 1,300 years before the world returned to warmer temperatures.

The imprint of pollution can also be measured in ice cores. Gases trapped in the air cells show clearly an increase in atmospheric CO₂, methane, and nitrous oxides, starting around 1800, about the time the Industrial Revolution got under way. Another, more menacing, type of pollutant that can be measured in the ice cores is radioactivity. In 1986 the Chernobyl reactor exploded, killing 250 people and spewing radioactive fallout across the world. Within only two years researchers coring the Antarctic ice cap had found a record of that dreadful day entombed in the ice as an excess of radioactive elements. Deeper drilling in both the Antarctic and the Arctic clearly show the onset of atomic bomb testing in the 1950s as well as a radiation spike resulting from the frenetic testing that took place in 1965, just before the Test Ban Treaty came into effect. The ice cores of Antarctica show a consistent decline in radioactive fallout since that year.

Finally, one of the more esoteric chemical markers to be found

in ice cores is sodium. Sodium is an integral element of that most common of seawater constituents, salt, and it turns out that it can be used as a marker for storminess. In colder periods the latitudinal temperature gradient between the equator and poles is increased and this has the effect of forcing the heat transport engine into overdrive. The heat transport engine is the shorthand name for the process by which the excess warmth of the tropics is transported to the poles either by surface water currents or by air movements. Climatic cooling, whether it is on a short (decadal or century) or a long (millennial) timescale, tends to cool the poles more than the tropics. This forces the heat transport engine to work harder. With the heat engine working harder, the winds and, therefore, the waves, are driven to higher intensity, too, and more of their sodium-laden spume lands on the icecaps. Sodium levels in both the Greenland and the Antarctic ice sheets show that there was a marked increase in storminess around 1400 AD, a time when there was a short period of intense cold that has been nicknamed “the little ice age.” At exactly the same time the archaeological record shows that Viking colonies in Greenland disappeared. Could it be that the increased storminess of the little ice age cut the Viking homeland off from its colonies, putting an end to the expansion plans of this ancient sea-faring race?

There is much to be gained from the study of ice cores, and the enthusiastic Vostok team drilled deeper and deeper until one of the most extraordinary scientific discoveries of the twentieth century forced them to stop. It was a discovery that would have fascinated the Challenger’s Scientifics, too because it was the evidence that they had set out to find in the first place—living fossils.

Termination Land, 61° 18′ S, 94° 47′ E

On February 16, 1874, Challenger was as far south as she was destined to go, a latitude of 66° 40′ S and a longitude of 78° 22′ E. She was on the edge of the Great Ice Barrier and only 1,400 miles

from the South Pole, the attainment of which would engender so much heartache and privation for the expeditions of Amundsen, Scott, and Shackleton a few decades later. But Nares was under strict orders not to try to proceed any farther. Both victuals and coal were in short supply and the risk of getting trapped in the ice was too great. They would certainly not survive a winter in those grim latitudes. As Wyville Thomson put it, “As the season was advancing, and as there was no special object in our going farther south, a proceeding which would have been attended with great risk to an unprotected ship . . . once or twice the water began to show that ‘sludgy’ appearance which we know ‘sets’ so rapidly, converting in a few hours an open pack into a doubtfully penetrable barrier,—Captain Nares decided upon following the edge of the pack to the northeastward, towards the position of Wilkes’ ‘Termination Land.”’

The expedition’s orders made it clear that proving the existence or otherwise of Wilkes’s Termination Land was a priority. As recently as 1840 Captain Wilkes of the United States Navy had written,

In fact, the idea of a continent in these southern regions was a lot older than Captain Wilkes. As early as the beginning of the eighteenth century, a continent had been marked on early charts, in the complete absence of any hard geographical data, and given the name “Terra Australis Incognita.” Its existence was hypothesized because the geographers of the day felt that something was needed

to counterbalance the weight of the continents of the high northern latitudes around Greenland and the Arctic.

By the 23rd of February Challenger was approaching the area marked on the charts as being where Wilkes had spied his great continent, but there was nothing to be seen. The weather was fair, with a slight breeze from the northwest that fell away to nothing by noon. All hands strained their eyes for some glimpse of land but to no avail. It seemed inconceivable that such a landmass should be invisible at such close proximity. There were icebergs aplenty, however, as well as strange cloud formations. Joe Matkin wrote, “On several occasions land had been reported from our mast head, and had it not been for our having steam, we might have marked new lands down on the Southern Charts; but although we could all have sworn that we saw land on one occasion, on steaming towards it, it proved to be a peculiar and remarkably defined vapor cloud. We have passed over several spots marked on the Chart as “Indications of land” without finding any and I daresay a steamship would dispel several of the mythical discoveries in this part of the world.”

By evening they had steamed right up to the edge of the pack but still there was no sign of land. The view, however, was beautiful. Wyville Thomson wrote, “The ship and the ice were for a time bathed in an intense yellow light, which faded into a delicate mauve, with cold patches of apple-green between the clouds. A long roll of heavy cloud stretched across the sunset sky, and the golden glow which it took after the sun went down was truly magnificent.” During the night the weather changed. By daylight on the morning of the 24th the wind was rising fast; the sky was dark and threatening, with frequent snow squalls that blew across the ship blinding clouds of wheel-like crystals so intensely cold that they burned when they touched the skin. At 4 A.M., they deployed the dredge in the hope of getting something before the weather got too bad but had to pull it up before it passed 1,300 fathoms. It was time to seek shelter and this Nares did by bringing Challenger into the lee of a large iceberg. The idea looked good until, during a

sudden lull in the weather, Challenger lunged forward and ran into the giant berg, smashing the jib boom and dolphin striker and carrying away several other items of the head gear. By now the sea was running hard, Force 10 on the Beaufort scale, estimated Wyville Thomson, and the euphoria brought on by the beauty of the ice pack was being rapidly replaced by terror at the thought of an icy lonely death.

It was indeed the coldest day that Challenger had yet experienced and in the violent seas she lay to under bare poles, just trying to survive. By lunchtime fog had descended and visibility was reduced to less than 50 yards. At 3 o’clock that afternoon it lifted just enough for them to see a large berg drifting directly toward them. The ensuing confusion, wrote Joe Matkin, “was something fearful; nearly everyone was on deck, it was snowing and blowing hard all the time; one officer was yelling out one order, and another something else. The engines were steaming full speed astern, and by hoisting the topsail, the ship shot past it in safety.”

The storm raged all night and three lookouts were posted. Nine times that night Challenger put about to avoid collision, and by the morning of the 25th the ship was covered in half an inch of snow. Despite the weather, the ship’s two carpenters were busy and by the 26th they were able to replace the jib boom. But the weather was still dirty and Nares himself spent that entire night out on the deck seeking shelter among the bergs when he could, or running from them when prudence dictated. “It was,” wrote Matkin, “considered the worst and most dangerous night we have had. . . . Altho’ we were all eager to see an iceberg, we are just as anxious to lose them now, it is so dangerous sailing these foggy nights with such masses of destruction all round us.”

There was still no sign of Termination Land so the hunt for it was abandoned. Spry wrote, “Wilkes’ vision was at fault, and the great Antarctic continent has turned out to be a Cape Flyaway. . . . Having now proceeded as far south as practicable in an undefended ship, at noon course was altered to the east. . . . On reaching clear

water studding sails were set and we were off for Australia, Cape Otway, 2, 278 miles distant.”

So Challenger turned its back on the Antarctic, much to the relief of all aboard, from Captain Nares and Charles Wyville Thomson down to ship’s steward’s assistant Joseph Matkin. But all aboard would have been aghast to know the scientific discovery that they were turning their back on, a discovery that would be made a hundred years later by the Vostok Ice Core team.

In the mid 1970s—almost exactly a hundred years after Challenger was in the region—an airborne radar survey of the ice sheet around Vostok Station revealed the presence of an enormous freshwater lake, beneath the ice sheet, that covered an area of about 10,000 square kilometers. By the early 1990s observations from satellites confirmed the presence of the lake, which was named Lake Vostok, and the news was released to the public by the Russian and American scientists who made the discovery.

The news caused a sensation, because the central question was obvious to all: How could a lake of liquid water survive under 4 kilometers of ice in the coldest region on Earth? The answer is simple: The ice sheet is heated from below by heat flowing outward from the interior of the Earth, known to geophysicists as the geothermal flux. Add to this the fact that 4 kilometers of ice is an excellent insulator and the presence of liquid water becomes understandable. The phenomenon is much the same as that which allows pools of water to accumulate below the slow-moving glaciers of the Swiss Alps, but on a vastly expanded scale in the Antarctic.

In the mid 1990s the Vostock scientific team had put together all the data that had been collected over the past 30 or so years and added new findings to provide a fuller description of Lake Vostok, and their interpretation was extraordinary. The lake was not only

huge, it was in places extremely deep, as much as half a kilometer. Although early estimates had suggested that the water in the lake might be quite old—at least 50,000 years—as knowledge of the lake grew, it seemed likely that the deeper parts were cut off from the usual circulation pathways (by which water arrives by melting of the surrounding ice sheet and leaves by sliding out from under the ice at the lowest point of the lake) and might be very much older, perhaps as much as one hundred million years. The implications of this finding were staggering, because it meant that it might be possible to sample liquid water that was contemporary with the dinosaurs. Before drilling was stopped to preserve this pristine, ancient environment, microbes—bacteria and fungal cells—were found in the lowermost layers of the ice cores. Today it seems likely that Lake Vostok is a repository for ancient life, a true lost world of which Conan Doyle’s Professor Challenger (probably another namesake because Conan Doyle studied under Wyville Thomson in Edinburgh) would have been proud, and which the Scientifics aboard HMS Challenger would have given their eye teeth to find.

This is the irony, of course, for as we have seen, one of the main reasons for the voyage of HMS Challenger was the desire to test the Darwinian notion that the oceans would be the repository for life forms that were, from the evidence of the fossil record, thought to be extinct. It turned out, however, that the ocean bottom was not so much the lost world that they sought, but rather a lake under an ice cap. However, it was a lake that was as inaccessible to them as the surface of another planet. So Challenger got within a thousand miles of Lake Vostok and the answer they sought before turning obliviously north for Melbourne and warmer climes.

Today one wonders whether any of the Scientifics could have had any inkling of what they might be missing by turning their backs on Antarctica. Almost certainly not. But the presence of these ancient bacteria and fungi has implications beyond merely those of evolutionary curiosity, because with modern techniques of DNA sequencing (in conjunction with the so called polymerase chain reaction) we really can now assess the genetic structure of life forms

thought to be long dead. This has huge implications for the pharmaceutical industry because it offers the prospect of a completely new set of templates on which to base drugs. The waters of Lake Vostok could be the greatest natural pharmacy in the world.

But there is more, because it turns out that Lake Vostok is not unique. Since its discovery back in the 1970s at least 70 other sub-Antarctic lakes have been discovered, most of them in the same area of the East Antarctic ice sheet. But if Lake Vostok is not unique, there is still one place for which it and its companions might well be a unique analogue, and that is Europa, one of the moons of Jupiter. Europa, like Antarctica, is covered by a thick sheet of ice, only in Europa’s case it is frozen methane, not frozen water. Soundings from spacecraft show that there is liquid water under this unimaginably cold crust, which immediately leads us to ask: If there is life under the Antarctic ice sheet, could there also be life under the Europan ice crust? The National Aeronautics and Space Administration (NASA) certainly takes the possibility seriously, and that is why drilling has been stopped at Lake Vostok. The lake provides a perfect opportunity to test the techniques that will be needed to sample alien life forms without contaminating either their environment or ours. The scientific community is now hard at work devising robots that can be rigorously sterilized before being sent down to sample the ancient waters of Lake Vostok. They will be the progenitors of the unmanned probes that we send to search for alien life.

In the late 1970s the first indications of Europa’s true nature began to emerge during the flyby of Voyager II, the second of the pair of space probes sent to explore the outer planets and their satellites. The Jupiter system is so far from the sun that our star is merely a flicker in the distance, a firefly glow that gives no warmth.

The Voyager missions were, for their time, every bit as ambitious as the voyage of HMS Challenger, and it is ironic that they were approved by the U.S. Congress at about the same time that Lake Vostock was discovered, a hundred years after Challenger started out on its own epic journey.

The impetus for the Voyager mission was to exploit a rare configuration of four of the outer planets, Jupiter, Saturn, Uranus, and Neptune, which occurs only every 175 years. This configuration meant that a spacecraft could visit each of the four planets using the “gravity-assist” technique perfected on an earlier Mariner mission to Mercury to slingshot its way between them. This eliminated the need for vast quantities of propellant as well as large on-board propulsion systems. It also meant that the journey time to Neptune could be reduced from 30 years to just 12. Although the “four-planets” mission was known to be possible it was judged that the likelihood of a spacecraft lasting the distance was so low that the mission was initially limited to visiting just the nearer two, Jupiter and Saturn.

Indeed, the likelihood of failure was judged to be so great that two identical spacecraft were built and named Voyagers I and II. So far from the sun would the Voyager spacecraft venture that each was equipped with a controversial nuclear power supply. They were launched in the late summer of 1977 from Cape Kennedy in Florida. Voyager II left first, in late August, on a slower trajectory that would allow it continue with the four-planets mission if by some miracle it survived. Voyager I left in early September on a shorter, faster trajectory that would send it north out of the Solar System after its encounter with Saturn.

Voyager I arrived in the Jupiter system in March 1979 and almost immediately made a spectacular discovery. Io, one of Jupiter’s moons, showed evidence of localized but extreme volcanism. This was astonishing, because volcanism showed that this moon was at least locally warm with temperatures of up to 15°C, perfectly warm enough for life.

Voyager II was due to encounter Europa within months. Scientists wondered if Europa too would provide surprises like those at Io. It was already known from long-range, ground-based spectroscopic studies that the surface of Europa was covered by a thick layer of ice. If there was volcanism on Io, could there not be

volcanism on Europa, too? And if there was, could there not be life there as well?

In those days all deep-space probe missions were run from the California Institute of Technology’s Jet Propulsion Laboratory (JPL) in a massive, amphitheater-like room not unlike Mission Control in Houston, which oversaw the manned Apollo missions to the moon.

On the evening of the Europa flyby several luminaries, including the sage of the search for extraterrestrial intelligence himself, Carl Sagan (with a group of his students), assembled to watch on the overhead monitors. The telemetry was primitive and as they waited, the group speculated about what they might find and how they would know whether there were volcanoes under the Europan ice sheet. The suspicion was that some hint of these buried volcanoes would be visible as smooth patches where the ice had locally melted and erased any hint of craters left by ancient meteorite bombardments. Smooth patches would indicate recent volcanic activity. But they were not ready for what they saw when the first image grainily established itself on the screens.

As the image slowly coalesced they saw, not a partially pockmarked ball of ice indicating localized volcanism and ancient meteor bombardment, but a perfectly smooth sphere of ice with no evidence of meteor bombardment at all. The conclusion was inescapable and its implication undeniable: The surface of Europa was being continuously cooked by global under-ice volcanism, and there was a massive planet-girdling water ocean underneath the ice cap. Europa was suddenly the best candidate for extraterrestrial life anywhere in the Solar System.

Amazingly it was to be 18 years before the JPL returned to Europa for another look with better equipment. Part of the delay was because of pressure on NASA and JPL resources to operate other missions and part was due to the catastrophic explosion of the space shuttle Challenger in 1986, which effectively shut down America’s manned and unmanned space program for two years. (The Challenger—Orbiter Vehicle-99—was also named in honor of

HMS Challenger, as was the final lunar module capsule to land on the Moon during Apollo 17.) But eventually new missions were planned and launched. In 1997 the Galileo spacecraft reached Europa, equipped with the latest in imaging equipment and the very first thing that it showed was the presence of icebergs on Europa. This could mean only that in places the ice was being warmed enough to break the shiny smooth shell that encircled the globe and allow chunks of ice to tilt. It meant, too, that the water ocean that had to underlie the ice sheet on Europa must be relatively close to the surface, perhaps as shallow as a mile. The Europan ice sheet was probably thinner than that of Antarctica.

Today the consensus is that there is an ocean of water, probably salt water, underneath the Europan methane ice sheet. The question of whether there is life in that ocean must remain open until we can send a probe to land on Europa. Objections have been raised that so far from the sun there is not enough free energy to support the type of life based on photosynthesis with which we are familiar. However, this might not be a problem, because the same energy that maintains water in a liquid state on Europa, the massive gravitational tidal forces of Jupiter and its satellites Ganymede and Io, could support life similar to that found near deep-ocean hydrothermal vents on Earth. Another suggestion is that life could tap the energy of the charged subatomic particles that swirl through the Jovian satellite system powered by Jupiter’s magnetic field.

The next step is to send a probe to land on Europa and sample it directly for life. However, the same concerns about contamination that stopped the drilling just above Lake Vostok apply, perhaps even more directly, to the idea of exploring Europa. At present JPL is developing a robot probe to explore both Lake Vostok and Europa. The Lo’ihi Underwater Volcanic Vent Mission Probe is currently being tested in an investigation of an undersea volcano 20 miles southeast of Hawaii’s Big Island at a depth of more than a kilometer. The probe was specially constructed to withstand the most stringent

sterilization procedures, and operate in extremes of temperature and pressure.

As I write this, the Voyager spacecraft are still functioning after more than 25 years in space, four times longer than their design lifetime. They are now the most distant human-made objects in the galaxy. Voyager I visited Saturn and then, constrained by its more limited trajectory, started to leave the plane of the ecliptic heading north. Voyager II was able to exploit its slingshot orbit and visit both Uranus and Neptune, thereby fulfilling the original four-planet mission envisaged by the mission designers all those years ago. It is now heading out of the Solar System to the south of the ecliptic. Both spacecraft are well on their way out to the heliopause, the place where our Sun’s influence finishes and the galactic wind of interstellar space starts. Like the voyage of HMS Challenger itself, theirs is an epic voyage of scientific discovery; but unlike Challenger, the Voyager spacecraft will not be returning home.

We salute them.

Arrival. Melbourne, Australia, 37° 45′ S, 144° 58′ E

It took Challenger 16 days to make the passage from 61° 18′ S, 94° 47′ E (the position of Wilkes’s mythical Termination Land) to Melbourne. After the rigors of their Antarctic sojourn those aboard might have been forgiven for hoping for an easy run, but it was not to be.

On March 2, 1874, they almost ran into a large berg during the middle watch. The frequency of bergs had declined so much that they were no longer running under reefed sails and were bowling along at a brisk pace. Swire wrote,

On top of this, food was running short. They were down to their last sheep, and after that they would be out of fresh meat. Swire had mixed feelings about the fate of the poor animal. “We have only got one live sheep left and after he is killed have to trust to preserved grub and ship’s provisions, which I much deplore. I fancy the feelings of the last sheep out of the forty that we took on board at the Cape; he who wrote about the “Last Man,” could perhaps likewise depict the harried sensibilities of this, our last mutton. I really think that after surviving the thirty-nine chances against him he is deserving of his life. But we are selfish where it concerns our interior economy, so I fear old fleecy-back must die.”

By March 15th they were approaching Melbourne, Australia. The sense of anticipation aboard the ship was palpable and all hands applied themselves to the task of making Challenger look presentable. It was also the day that they made contact once again with the human race. As Swire put it, “Today has been a beautifully fine, dry day and this afternoon a phenomenon appeared on the horizon in the shape of a full, rigged ship, the first we have seen for many a weary day. Preparations for Melbourne are in full swing on board, now; paint and whitewash are being slapped about in the most promiscuous manner, so that one is half poisoned by the smell of turpentine etc. I shall try to get in shore as soon as ever we drop anchor.”

On March 17, 1874, Challenger dropped anchor off the leafy suburb of Melbourne known as Sandridge. Except for the exploration of Marion Island and Kerguelen, they had been three months at sea without setting foot on land.