While space may be considered the "last frontier," there are others, such as oceanographers, underwater archaeologists, and treasure hunters who would say the oceans, seas, lakes, and lagoons are the real "final frontier" when it comes to discovering what makes planet earth, tick.

In water masses around the world, there have been discoveries of ancient cities, sunken war ships and planes, pirate treasure, mysterious walkways, prehistoric bones, exotic microorganisms, and much more.

Links to ancient artifacts and the stories they have to tell are a direct link to the planet's history and how it has affected its inhabitants. Access to relics from the past to the present is a timeline filled with invaluable knowledge that fills in the blanks and provides new insight into how people have lived on earth for thousands of years.

Space exploration is definitely a frontier of its own to be explored as are the secrets held in the watery depths just waiting to be discovered.

25 USA: A 14,500-Year-old American Mastodon, Florida

At Page-Ladson, the oldest southeastern archaeological site, the discovery of mastodon bones and tusks, as well as well-preserved dung, has taken scientists by surprise. For years, the belief was people inhabited North America 13,000 years ago. After carbon dating of the material of the mastodon was completed, it has been verified that people were inhabiting the area 14,500 years ago. This is a significant discovery. The site, located in the Aucilla River, was first reported in the 1980s and has been researched and excavated extensively.

24 Europe: The HMS Stubborn - She Lived Up to Her Name, Malta

The WWII submarine was aptly named as it served its part in history from the day of its first mission to its last mission in 1945. The HMS Stubborn began her commission in February 1943 when ordered to search for the missing HMS Vandal. In April of that year, she was sent on her first war patrol.

The sub continued patrolling the waters and engaging and attacking the enemy until August 1945 when, after completing 10 war patrols, the sub was decommissioned.

23 USA: Final Resting Place for a 1946 Corsair Plane, Hawaii

Resting at the bottom of the ocean in the waters of Oahu are the remains of what looks like at first glance is a giant whale. Upon closer examination, divers can clearly see the engine, wings, and cockpit of what has been identified as a vintage 1946 airplane. The Corsair - Chance Vought F4U - was on a training mission when it ran out of fuel. Luckily, the pilot was able to eject but the plane made its way to its watery grave where it serves as a reminder of the past as well as an interesting diving destination.

22 Europe: 9,500-Year-Old Lost City of Dwarka, India

In 1963 just off the coast of India, oceanographers discovered the remains of an underwater city, which has been identified as Dwarka, which was noted as being lost in 574 A.D in historical documents. Archaeological research has been on-going but limited due to the harsh conditions of the sea. Fragments of underwater structures, ridge-like structures, beads, inscriptions, pottery, and metal objects of iron, bronze, and copper have been recovered.

In the nearby Gulf of Cambay, another site was discovered that measures five miles in length and two miles in width and abundant with ancient artifacts including sculptures, jewelry, standing walls, and human bones. Carbon dating shows the artifacts to be estimated at 9,500 years old.

21 USA: To Infinity and Beyond and Back - Apollo 11 Engine, Florida

In 1969, the Apollo 11 mission made history as it was the first manned mission to the moon. On July 20, 1969, Neil Armstrong and Buzz Aldrin landed the lunar module on the planet. Armstrong's first words upon stepping on the moon's surface - "That's one small step for man, one giant leap for mankind" - have gone down in history signifying America's success in planetary exploration.

The two F-1 engines were recovered in 2013 by Jeff Bezos, CEO of Amazon.

20 Europe: Caesarea Sunken Treasure, Israel

In 2015, divers on an underwater adventure came across a gold coin in the waters near Caesarea National Park. Upon looking closely at the engravings, it was apparent the coins were more than a modern coin lost in the sea.

The proper authorities were notified, and the result was the recovery of an estimated 2,000 coins dating to the 10th and 12th centuries along with other period relics. So far, the find is estimated as "priceless."

19 USA: The Olympic II and the Titanic were Ship Mates, California

The Star of France, later renamed the Olympic II, sits idly beside the Titanic in this 1912 photo. The ship was built in 1877 in Ireland and initially served as a merchant vessel traveling the high seas. In 1905, she was sold and continued as a transport vessel until 1925. In 1933, the ship was purchased and renamed the Olympic II used for fishing. In 1940, the Olympic II was violently struck by the Sakito Maru, a Japanese freighter. Within three minutes, the ship sank and eight crew members of the Olympic II perished in 100-feet of water in the Pacific.

18 Europe: Marianas Trench - Deepest Place on the Planet, Mariana Island

If you've ever thought about exploring the deepest place on the planet, the Marianas Trench would be at the top of the list. In 1875, scientists aboard the HMS Challenger used a device to record the depth to be five miles. It was measured again in 1951 by the HMS Challenger II at seven miles. In 1960, the first manned mission. on was undertaken by Navy Lt. Don Walsh and Jacques Piccard. The descent to the ocean floor took five hours.

The trench is dark and freezing with extreme pressure indicating lifeforms consist mainly of microscopic inhabitants able to withstand the extreme conditions.

17 USA: A Treasure Trove Aboard the SS Central America, South Carolina

Divers hit the "jackpot" when the SS Central America was recovered. The 280-foot wooden-hulled steamship lined with copper sheathing and touting 3-masts sunk on September 12, 1857, when it came face to face with a hurricane. The steamship was a busy vessel during the California Gold Rush era as it was used to carry large parcels of gold.

When it went down, it was loaded to the gills with gold ingot and Double Eagle coins. Because the cargo was so massive, when it was lost, it had a negative effect on the economy at that time. The location of the ship was confirmed in 1988 at 7,200-feet with recovery efforts for the cargo, which included numerous artifacts, being a continuous project.

16 Europe: Untouched 8th Century BC City Thonis-Heracleion Found, Egypt

After 1,200 years, the mystery of what happened to the city of Thonis-Heracleion was revealed by archaeologist Frank Goddio. Thonis-Heracleion dates to the 8th century BC and was a major shipping port. The theory is the city was faced with cataclysmic conditions that resulted in its being submerged into the Mediterranean where it had lain untouched. The site is an archaeologist's dream come true.

Numerous discoveries have been made including buried ships, 16-ft. statues, inscribed stones, anchors, gold coins, and much more.

15 USA: An Authenticated Pirate Ship: The Whydah Gally, Massachusetts

"Yo ho ho and a bottle of rum" might be what the crew aboard the pirate ship captained by Sam Bellamy was singing when they captured the Whydah Gally during its maiden voyage in 1715. The ship was built as a slave ship, but the pirates had other ideas and turned the 100-foot ship into a pirate ship.

In 1717, the ship sank in sight of land during a heavy storm. Divers discovered the vessel in 1984 and its cargo, which had remained pretty much intact, contained gold coins, silver, weapons, muskets, gold belt buckles, and the ship's bell with the name of the ship inscribed on it, which served as proof in identifying the ship. Over 200,000 artifacts have been recovered from the ship.

To date, it is the only positively identified and authenticated pirate ship to be recovered.

14 Europe: Astronomical Mechanism Found at the Antikythera Shipwreck, Crete

One of the most bountiful shipwrecks that produced some of the oldest relics was first discovered by sponge divers in 1900 near the island of Antikythera near Crete. The ship dates to the First Century BCE and was used to transport artwork to Rome. Numerous pieces have been found including full-size bronze statues, glassware, pottery, tankards, jewelry, human bones, and parts of the ship. One piece is referred to as the "Antikythera mechanism", which has been determined to be an elaborate and sophisticated astronomical device.

Recent searches indicate that there is an estimated 7 to 9 bronze statues buried under boulders to be uncovered and placed in the Athens National Museum.

These unusual looking sea inhabitants have been referred to as "chocolate cookie dough" creatures due to their "chocolate" dots covering their leathery beige skin. There are over 1200 species of the pliable three-row sea cucumber. Although it is relatively docile, the sea cucumber does have toxins that are lethal to small invertebrates and if threatened, could be problematic if the toxin comes in contact with the eyes.

Most sea cucumbers inhabit the ocean floor, but a few thrive near the surface. Recently, all-white (albino) sea cucumbers have been discovered off the coast of Mexico.

12 Europe: Bimini Road, Bahamas - Is it the Road to Atlantis?

Beneath the emerald-green waters of the Bahamas lies a length of stone road reaching 1/2-mile that many believe led the way to the lost city of Atlantis. The stone pathway, known as the Bimini Road, was first discovered in 1968 by Joseph Mason Valentine, a subsea archaeologist along with his diving team.

An interesting tidbit about the discovery was in 1938 psychic Edgar Cayce predicted there could be a discovery near Bimini with evidence of ancient temples in 1968 or 1969. Eerie, since 30 years later that's what some believe has happened.

Another point of interest; the name Bimini appears throughout ancient Egyptian as "Baminini." While there are those who believe the perfectly formed slabs of stones are a result of nature others are convinced the road leads to Atlantis.

11 USA: Locomotive Graveyard, New Jersey

An unusual find in New Jersey waters is shrouded in mystery. In 1985, a boat captain doing ocean floor surveying discovered the train graveyard with two vintage Planet Class 2-2-2 T model steam engines sitting idly on the ocean floor just waiting to make their next destination. The engines are at a depth of 90-feet and well-preserved considering it's estimated they have been in the ocean since the 1850s. The assumption is the trains must have fallen off a transport ship during a severe storm.

10 Europe: Truk Lagoon - The Motherload of WWII Artifacts, Federated States of Micronesia

The divers experienced a visual history lesson about World War II when an expedition led by Jacques Cousteau in 1969 to Truk Lagoon (now known as Chuuk Lagoon) revealed the sites historic significance. The lagoon played host to Operation Hailstone on February 16/17, 1944 when American planes launched an aerial attack on anchored ships. Truk Lagoon was a major naval base with an extensive infrastructure for the Japanese Imperial Navy, which meant it was heavily fortified. Because of this, the base had earned the nickname "the Gibraltar of the Pacific."

Over the ensuing days, the Japanese fleet lost an estimated 10 warships, over 30 supply vessels, 275 aircraft, light cruisers, and destroyers, and an estimated 4,500 military personnel during the two-day strike. Along the ocean bottom are remnants of the ships, its cargo such as tanks, automobiles, motorcycles, guns, radios, medical equipment, and human bones. The site has been designated as the Truk Lagoon National Monument.

9 USA: Stonehenge-Mysterious Above and Below Water, Lake Michigan

This is Stonehenge in England, now, imagine a smaller yet similar rock structure under the waters of Lake Michigan. In 2007, underwater archaeologist Marc Holly from the Northwestern University of Michigan discovered the unusual structures while on a research expedition. The position of the Lake Michigan Stonehenge "circle" is pretty clear that it is man-made.

Also found was a large boulder with a carving of a mastodon clearly depicted. This added even more mystery to the site. Estimates dating the site are at 9,000 years.

8 Europe: The Vasa - Shortest Maiden Voyage on Record, Sweden

The ship is a real beauty. Sunk in 1628 in Stockholm Harbor, the well-preserved ship was raised in 1961, restored, and put on display in its own museum. The Vasa has had an interesting journey that took over 300 years from her initial sinking just minutes after leaving port on her maiden voyage to her recovery in 1961. The warship was a prized possession and one the king wanted to be the best of the best. When it sunk so quickly, the blame was put on the designer.

The recovery and restoration of the Vasa was an on-going project for many years to maintain the 17th-century warship that was 98 percent preserved. In 2017, the Vasa was named as a top ten attraction in the world.

7 USA: Queen Anne's Revenge, North Carolina

Pirates were busy along the east coast of America and this artifact is another example of how treacherous the ocean could be back in the day. In 1718, the Queen Anne's Revenge, captained by no other than Blackbeard himself, set up a blockade in Charleston Harbor. He intentionally ran the ship aground off the North Carolina shoreline. The ship wasn't found until 1996 by Intersal, Inc. and has provided researchers with more than 250,000 artifacts, including over 30 cannons, which proves Blackbeard was a pirate to be reckoned with on the high seas.

6 Europe: Most Visited Underwater Museum: SS Thistlegorm Wreckage, Red Sea

The SS Thistlegorm was a 400-foot battleship sunk by Japanese bombers during WWII. The attack was a surprise catching the crew off guard. When found in 1955 by Jacques Cousteau, the ship's cargo was mostly still intact. The ship carried equipment such as military tanks, trucks, jeeps, Norton motorcycles, guns, ammunition, and even Stanier BF locomotives, which were on the deck and ultimately thrown into the Red Sea.

Today, the SS Thistlegorm is touted as one of the world's most visited underwater museums for divers.