In the late 1950s, at the height of the Cold War, competing teams of US and Soviet scientists began a series of experiments. These experiments involved drilling down deep into the earth’s crust, the thin shell on the outside of Earth, thought to stretch as far as 30 miles towards the centre of our planet.
The shell eventually gives way to the mantle, a layer of silicate rocks between the Earth’s crust and the outer core. With a thickness of 2,900 kilometres, it makes up a staggering 84% of Earth’s volume. The American’s and Soviets aimed to reach the mantle.
The race was on. The two superpowers competed with one another, with the ultimate aim to be the country who had dug furthest into the Earth's crust. The idea was to provide an earth science addition to the high-profile Space Race.
In 1958, the US took the lead with Project Mohole. A team of engineers drilled through the bed of the Pacific Ocean, at a location near Guadalupe in Mexico, until they reached 600 feet deep. The mantle is easier to access this way, since it lies a lot closer to the sea floor. However, Project Mohole had to be abandoned eight years later since their funding was cut. They never reached the mantle.
Next, it was the Soviet's turn to dig down deep. On May 24, 1970, a group of researchers began to drill down into the earth below the Pechengsky District, a sparsely populated region on Russia's Kola Peninsula.
Their goal was simple: to see how far into the earth's crust they could penetrate. They were determined to do better than the Americans had. Confident that they had enough funding to keep them going, they prepared to dig.
The Soviets hoped to reach a depth of some 49,000 feet under the Earth's surface. The plan was set into motion, with the team using specialist equipment. They used the Uralmash 4E, and later the Uralmash-15000 series drilling rig.
The boreholes were drilled forking off from a central hole. While they slowly made their way down into the deep depths of the earth, the Americans were making some significant progress of their own. The game was on!
In 1974, the Lone Star Production Company was drilling for oil in Washita country in Western Oklahoma. In the process, they created the "Bertha Rogers hole." Over a period of just over a year, the team managed to reach 31, 441 feet, the equivalent of six miles below the surface of the Earth.
While Lone Star did not find what they were looking for, they had dug the deepest manmade hole on the planet. It remained this way for five years, until June 6 1979. This was the day that one of the Kola boreholes, SG-3, claimed the title. By 1983, the hole, just nine inches in width, had reached the astonishing depth of 39,000 feet.
With this milestone achieved, workers on the Kola Peninsula temporarily put down their tools. They took 12 months off in order both to give themselves a break and to give people a chance to visit the incredible site. They resumed work the following year but soon encountered some complications which meant that the work could not continue.
Determined not to let this defeat them, the researchers abandoned the previous borehole and started again, this time from a depth of 23,000 feet. By 1989, the drilling had reached a record 40,230 feet - an incredible 7.5 miles. This filled the workers with optimism again and they became confident that the hole would pass 44,000 feet by late 1990.
Still more incredible, it was estimated that the hole would reach its target of 49,000 feet by as early as 1993. The workers didn't know it yet, but they were about to discover something quite amazing lurking beneath this remote Russian tundra. As the drill inched ever closer to the Earth's centre, it was met with an unexpected change.
Researchers were more or less correct about what the temperature would be for the first 10,000 feet down. However, when they went beyond this point, they found that the temperature shot up considerably and at a much faster rate. By the time the drilling had begun to reach its target, the hole had heated up by 180°C (356°F) - a whole 80°C (176°F) hotter than they had anticipated.
In addition to this, the researchers discovered that the rock at these depths was far less dense than they had thought it would be. This meant that it reacted with the temperature in unpredictable ways. The team knew that there was no way that the equipment would be able to survive these conditions, so they had to abandon the project. It was now 1992 - 22 years after drilling had commenced.
The researchers had discovered some incredible things before they had to seal up the hole, which is now referred to as the "Kola Superdeep Borehole." When they had reached around four miles in-depth, they came across some tiny fossils of marine plants. They were extremely well preserved considering the fact that they had been buried below miles of rock. The rock in question was believed to be over two billion years old.
At the farthest reaches of the Kola Superdeep Borehole, and even more exciting discovery was made. Up until this point, it had been predicted by scientists, after measuring seismic waves, that rock under our feet shifts from granite to basalt at around two to four miles beneath the surface. However, on the Kola Peninsula, they found that this wasn't the case.
Instead, they found only granite at the deepest point of the borehole. As a result, after doing some extensive research, they came to the conclusion that metamorphic differences in the rock were the reason for any changes in seismic waves, rather than a shift to basalt.
They also discovered flowing water several miles beneath the Earth, at depths that no one had ever predicted water might be. While some have jumped on this with comments that this provides us with evidence of biblical floods, there is actually a scientific explanation for this. It is believed that this has happened as the result of strong pressure forcing oxygen and hydrogen atoms out of the rock. Following this, the newly formed water became trapped beneath the surface.
The timing of the Kola Superdeep Borehole's closure coincided with the fall of the Soviet Union and by 1995, it had been shut down and would remain that way permanently. Today, the site itself is said to be an environmental hazard, but it is possible to see some of the relics from the experiment in the nearby town of Zapolyarny. To this day, it remains the planet's deepest man-made point.
The race to the centre of the Earth doesn't end here. Representatives from the International Ocean Discovery Program continue to delve deep below the sea floor, in the hope of unearthing more exciting secrets.
Not every underwater expedition is an attempt to reach the centre of the Earth. One particular group who also decided to brave the depths of the deep blue had a slightly different aim. Dropped into the cold waters of the Antarctic in a two-man submersible, this crew wanted to go deeper under the waves near the South Pole than any other expedition in human history has ever done. Once they were down there, they discovered something that no human had ever set eyes on until then.
Two years of meticulous research had gone into finding the perfect time and location in order to make this immense dive. This was crucially important since we don't know a huge amount about the Earth's ocean floor. We have a much better insight into other planets.
In fact, we have managed to map the surfaces of Mars in much greater detail than the ocean floor. To give you some perspective, the average distance between Mars and Earth is 140 million miles, while the average depth of the ocean is just over 120,000 feet, the equivalent to around 2 miles.
First of all, the scientists had to work out where the best place to begin the descent would be. After some careful consideration, they came up with an appropriate location, "Iceberg Alley." It is called this for a reason, a good one at that.
This alley forms a channel that is very close to one of the Antarctic Peninsula's northernmost points. This is a stretch of sea which is surrounded by chunks of shifting ice of varying sizes. This meant that ensuring that the boat reached the right spot was quite a challenge.
A documentary has been made about this incredible expedition and according to executive producer, James Honeyborne, they were met with various obstacles along the way. He explained to the BBC that making it through Iceberg Alley was just like being in a "giant game of Space Invaders."
Another concern was that the submarines the crew was using might not be able to withstand the strain of the deep water. As they descended into the water, these concerns melted away. They were immediately distracted by the breath-taking ecosystem of strange creatures they met below the surface.
Beneath the waters of the Antarctic lies an abundance of weird and wonderful sea creatures. "Within a square yard there is more life in the deep of the Antarctic than there is in the reefs of the Barrier Reef of Australia," one member of the dive team, Mark Taylor told LADbible.
There is a crucial reason for this. These sea creatures are surrounded by the matter which is referred to as marine snow, which, according to the University of Southampton's Dr. Jon Copely, "thicker than [he's] seen it anywhere else in the world's oceans."
What is marine snow, you may be asking? Marine snow is essentially organic material that falls in a continuous shower from the upper part of the ocean down to the seabed. It transfers nutrients and energy from the parts of the sea that receive sunlight to the parts that don't, therefore it is an important source of food for these creatures.
Another huge importance of food for the creatures this far down in the Antarctic is krill poo. Krill are tiny crustaceans whose excrement turns the seafloor into a muddy habitat which is perfect for sustaining life. The creatures this far down in the ocean are some of the most bizarre creatures there are.
One of the more strange creatures that inhabit the deep depths of the Antarctic is a strange relative of the common starfish, known as the Antarctic Sunstar. The researchers gave it the slightly sinister, but very fitting nickname: "Death Star."
The Death Star can have up to 50 arms and can become bigger than a dinner plate. The skin on its arms is covered with little pincers, and the moment anything touches them, they snap shut. Passing krill often fall victim to these deadly pincers.
The Death Star provides an example of just how strange and diverse the creatures are in Antarctica. Few fish are able to survive in the cold waters of the South Pole which means that invertebrates such as the Antarctic end up taking their place at the top of the food chain.
Diving in the sea is almost like looking through a window to the past. It gives you an idea of what life in the seas was like before humanity ever existed. "It's the animals without backbones that dominate and that dominate as predators," said Dr. Copley. "And that's how the oceans were more than 250 million years ago."
Another strange creature living in the Antarctic ocean is the ice dragonfish or Cyrodraco antarcticus. This fish has adapted some incredible features in order to ensure its survival in the ice-cold Antarctic conditions.
For example, its blood contains proteins that act like antifreeze in order to prevent it from icing up. Unlike human blood, their blood is clear since they have no need for haemoglobin to carry oxygen around its body.
There was, in fact, more to this expedition than simply discovering what fascinating creatures lay lurking in the depths of the Antarctic. Finding out more about exactly how life Antarctic Ocean survives could also play an important role in ongoing conservation efforts in and around the South Pole.
"On these dives, we watched the everyday lives of Antarctic deep-sea animals, helping us to understand them much better than studying specimens collected by nets or trawls from ships." Dr. Copley explained to the BBC. "And [it's] helping us to investigate how our own lives are connected to this remote yet fragile environment."
There continues to be a lot of mystery surrounding the oceans, including the parts of the Ocean that are fairly accessible. Dr. Copley hopes that this expedition will help towards changing that. "Sending people a kilometre deep into the ocean around Antarctica for the first time shows that there is no longer any part of our blue planet that is inaccessible to us if we can find the will to go there."
There's something hugely profound about going to a place that is so difficult to reach. "What we're doing now is an exploration in the purest sense," Dr. Copley stated. "If we all share in the exploration of our planet, then... we'll all feel involved in its stewardship for the future."