(CNN) Millions of years ago, precious gem stones from the heart of southern Africa washed westward along the Orange River and emptied into the Atlantic Ocean.

While some swept up on the beaches along the Namibian coast , spurring a diamond rush in 1908, others came to rest on the ocean floor. For a little while at least.

Today, six ships comb the ocean, sucking sediment from the seabed. The immense vessels are operated by Debmarine Namibia, a joint venture between the Namibian Government and diamond giant De Beers.

Last year the marine diamond mining company produced 1.378 million carats of diamonds, at a time when the country's land operations are waning.

To ramp up production, Debmarine Namibia plans to construct a $142 million ship-cum-tanker, which it says will be the world's largest custom-built diamond mining vessel , measuring 577 feet long. It hopes this new vessel will join the fleet by 2021.

This type of vehicle -- called a crawler ship -- has a 280-ton mechanical arm that moves in a horizontal arc, dredging material from just beneath the sea floor, at depths of around 400 feet.

Diamonds are then sifted from the dredged gravel in a sophisticated treatment plant onboard the ship. The gravel is returned to the ocean and the gems are securely sealed in containers, loaded into steel briefcases, and flown by helicopter to shore.

No human hands touch the diamonds during the entire production process at sea.

Gems in a haystack

Debmarine Namibia has a license to operate off the coast of Namibia until 2035 within a 2,316 square mile area -- just under half the size of Jamaica.

But, while the ships mine 24 hours a day, 365 days a year, they're not scouring every last square mile, explains Otto Shikongo, CEO of Debmarine Namibia.

"You only mine areas which are mineable and profitable," Shikongo tells CNN. "It doesn't mean that every place that you find diamonds you go mine."

He says Debmarine Namibia has depleted a total of 50 square miles since production began in 2002, just two percent of the license area.

"The resource is patchy and not homogenous," he says, adding that the future of the mining will depend on their understanding of the seabed and technological advances.

"It's not the same as a land-based resource which you can see with your eyes ... this one is 120 meters [393 feet] under the water," he says.

Every so often Debmarine Namibia sends out unmanned, autonomous vehicles -- much like underwater drones -- to survey the seabed using sonar technology.

The team also makes use of a two-person submarine to examine the geology of the seafloor.

Next, a 12,000 ton exploration vessel scoops large samples from areas that are believed to hold diamonds.

To date these combined technologies have identified a mineralized area -- or an area containing diamonds -- of 617 square miles. This makes up just over a quarter of the total license area.

The hope is to discover more diamond-containing areas through further exploration and sampling, explains Shikongo.

Debmarine Namibia's submarine examines the geology of the seabed.

Survival of the fittest

While marine diamonds may be difficult to find, they're certainly worth the hunt.

Shikongo explains how nature ensured that only the "fittest" diamonds survived the journey along the Orange River, while weaker, imperfect stones were destroyed.

"Because the diamonds went through a high energy process, almost like a tumbling effect, only the best, high quality diamonds survived and made it to the sea," he says.

As a result, Shikongo estimates that 95% of diamonds recovered from the sea are of "gem quality," compared to just 40-60% of diamonds from land operations.

Employees grade and store rough diamonds at the Namibian Diamonds Trading Company in Windhoek, Namibia.

Environmental cost?

But, in the search for these precious gems, thousands of tons of sediment is dredged up and then dumped overboard.

Marine scientists argue that seabed mining degrades the marine environment, potentially impacting marine species.

"The waters off the coast of Namibia are an important area for a high diversity of resident and migratory species, such as sharks, whales, dolphins and seals," Kirsten Thompson, a marine scientist from the University of Exeter, tells CNN over email.

"Marine mining removes parts of the seabed with heavy machinery and habitat recovery from this type of disturbance can take decades."

Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Thoroughly untamed: Extending 500 kilometers between the old German colonial town of Swakopmund and the Angolan border of Namibia's coastline, the Skeleton Coast is virtually uninhabited.

Hide Caption 1 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Eerie destination: It's named for the animal bones scattered across its strands as well as the many ships that have wrecked here over the centuries. Hide Caption 2 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Surf's up: Skeleton Coast boasts strong currents and several spectacular breaks that attract a small, but steady community of surfers. Hide Caption 3 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Ship skeletons: This wreck near Walvis Bay is one of the hundreds of doomed ships whose wooden or metal skeletons litter the area. Hide Caption 4 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Recent victim: The wreck of fishing trawler Zeila which was stranded near Henties Bay in 2008. Hide Caption 5 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Adventure sports: The only way to explore the northernmost part of the Skeleton Coast between Mowe Bay and the Kunene River is by joining a mobile tented safari with permission to travel in the restricted zone. Hide Caption 6 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Activity center: Founded in 1892 as the primary seaport for German Southwest Africa (later Namibia), the breezy coastal town of Swakopmund is now the southern gateway to the Skeleton Coast. Hide Caption 7 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Surf fishing: Upwelling of nutrients by the cool Benguela Current help to make offshore Namibia one of the world's richest fishing grounds, with Torra Bay one of the the area's main fishing camps. Hide Caption 8 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Bird life: Flocks of as many as 50,000 greater flamingos flourish in the shoreline's lagoons, estuaries and salt pans during the long migrations across the continent. Hide Caption 9 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Seal colony: The most common mammal along the Skeleton Coast, Cape fur seals live in colonies, with very large groups at Cape Cross and Angra Fria on the northern shore. Hide Caption 10 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Iconic creatures: The coast is home to the rare and endangered desert lion, sometimes seen stalking and feasting on marine creatures. Hide Caption 11 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Unique population: The Hoanib Research Centre strives to protect and conserve these noble beasts of the desert coast. Hide Caption 12 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Desert elephants: Smaller than their inland cousins, the elephants of the Skeleton Coast have other adaptations for their unique environment including longer legs and wider feet that ease walking on sand. Hide Caption 13 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Wild cat: The tuft-eared caracal cat is one of the many rare animals that inhabit this part of the Namibian coastline. Hide Caption 14 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Exceptional creatures: In addition to desert-dwelling lions and elephants, the Skeleton Coast is home to cheetahs as well as the tuft-eared caracal cat. Hide Caption 15 of 16 Photos: Namibia's Skeleton Coast: A journey through the 'end of the earth' Safari camps: Hoanib Skeleton Coast Camp is one of only a handful of classic safari camps or lodges along the entire length of the coast. Hide Caption 16 of 16

But Shikongo says Debmarine Namibia continually monitors its footprint.

According to Shikongo, the company's environmental monitoring program found that it takes between two to 10 years for the seabed, and associated marine life, to recover.

However, in rockier terrains natural recovery could take more than 10 years.

Thompson adds that diamond mining can impact ocean life through increased ship traffic, noise, light and pollution, and is just one of many activities degrading the marine environment.

"Marine species are already experiencing profound changes due to climate change and other human-related activities, such as fishing, plastic pollution and shipping," she says.

"Some species and habitats are simply not resilient enough to cope with these multiple stresses simultaneously."

Offshore mining is increasingly important for the diamond industry in Namibia, as land-based production begins to tail off.

"Land operations have been there since 1908," explains Shikongo. "So these resources are not finite as we know and as time goes ... production tends to taper down."

Debmarine Namibia commenced marine mining operations in 2002, with a haul of approximately 500,000 carats . At the time, sister company Namdeb's land operations were producing around a million carats.

But over the years the tables have turned and marine operations now account for close to 75% of total diamond production in the country, according to Namibia's Chamber of Mines

With all eyes on the Atlantic, the question remains: How soon will we exhaust this precious underwater resource?

Shikongo believes there are probably enough stones scattered across the Atlantic seabed for Debmarine Namibia to continue mining for at least the next 20 years.

The only challenge is finding them.