Not only have we mapped the entire ocean floor globally, we have also sent instruments, and probes deeper into the Earth than mainstream science suggests. MUCH deeper.
During these explorations over the years, we confirmed the presence of other intelligent life, including non-sentient life. But here's the kicker, it's native to Earth, as far as we can determine...
This is where it will get weird for you.
One of these ecosystems of life inhabits a region under the Earth's surface called the Asthenosphere. This zone is about 3 layers away from Earth's inner core. It is a partially molten region, with many pockets of solid "bubbles" that act as caves essentially, ranging in size from a few feet, to city, and country sized.
One of the species is SILICON based. Able to form 4 covalent bonds like carbon, it's the next best supporter of "life". That's about all the two have in common though. The beings discovered here thrive in temperatures ranging from 1000°c - 3500°c. Anyone that took grade school chemistry knows that silicon crystallizes in a diamond cubic crystal structure. You'd also know that macro structures will resemble their micro, and nano constituents. We've recorded these naturally occurring structures both underground, and deep under the hottest hydrothermal vents. Some of these structures appear to have been modified as dwellings.
There are simple creatures under the surface that we have estimated to have life cycles of millions of years, due having ultra-slow metabolisms. Some of these are chemosynthetic, and break down things like rock, or even molten rock. Basically they can, and do eat magma. There are also sentient beings...
These beings are not humanoid, as most ET's are depicted. Think of the body structure of an octopus, but much larger, and with like a head and 4 extra appendages attached to the top, and not so soft, and not at all translucent. No observable mouths, two eyes. Their form of locomotion has been observed, but it is not understood. The reason it isn't understood, is because they appear to be able to move through molten, and solid matter, at least what appears to be solid matter to us...
They have vehicles that can enter/leave the planet's atmosphere. Their composition appears to be some kind shape-changing exotic alloy that we have not yet identified. They have some kind of covering over their entire bodies. Not clothing, more like a transparent "shell" for lack of a better description. We believe this is due to the fact that silicon crystallizes when introduced to oxygen, so a silicon-based lifeform would need to either evolve natural protections against oxygen, or devise them technologically.
Communication has been established, and they are not hostile. They do however wish to be left alone for the most part.
OK, ready for more? There's another sentient species we've discovered. It's aquatic, and humanoid.
This aquatic species has been here for hundreds of thousands of years. They are hyper-intelligent, and have technologies that cause a lot of "unexplained" phenomena that we humans witness. A good portion of UFO sightings are their craft, which also traverse underwater (USO) at impossible speeds.
I have not seen anything of the silicon species except images of dead ones (captured and then intentionally exposed to high levels of oxygen), and data that would mean nothing to the average Joe on reddit. I have however seen this aquatic species in action, up-close.
I'm going to be intentionally vague here, but I worked for NOAA for a better portion of my career. This organization is actually pretty small, and lots of people know each other, and share data. The team I lead used multibeam echosounders fitted to vessels, to map the seafloor in astounding detail.
The information I'm disseminating here has been cultivated over decades of being around scientific "big wigs" in various related fields, and holding a prominent position myself after a few job changes. This information is not as protected as some of you may think. In fact, most of the upper-level politicians are aware, as NOAA and similar organizations are government funded/controlled. Militaries are aware as well, and most obviously the Navies of developed countries.
The control mechanism isn't "don't tell anyone or we'll kill you", it's more "don't tell anyone or we'll make you suffer in other ways(financially, socially etc), and no one will believe it anyways". So these things get out all the time, but they end up on conspiracy boards, because obviously no one believes them.
The aquatic species is more than likely to blame for historical mermaid sightings. They don't have a single tail fin like mermaids portrayed in media, they have two separate limbs that are not quite legs, but not quite fins. Imagine like two elephant trunks replacing where legs would go on a human, and you're close. I use elephant trunks as an example, because there are actually openings on the bottoms of these appendages, kind of like mouths, but they are actually used for propulsion through the water at high speeds.
We are still very in the dark about their biology, especially how they are able to exist freely at such depths and pressures. From what I've been told, the Russians were the first to encounter them, with early skirmishes ending fatally for some Russian Navy divers. Many submarine crews have had encounters, and gathered hard data on sonar, video, and audio. The audio recordings tell us they emit sounds that share similar markers to the noises that dolphins make to communicate.
More on their appearance; Humanoid with trunk-like appendages at the bottom of the torso. Milky white skin, completely black eyes, including the sclera. Hairless, extremely thin compared to the average human. Arms end with hands that look like a flipper, with 3 digits instead of 5 like us. Their mouths are very wide, and very thin, like a slit going from ear to ear, but they don't have external ears like we do, and from my personal observations, they likely have otoliths, a structure present in the inner-ears of most fish, that give them the ability to "hear", though it's closer to bone conduction.
We don't know how they see. From an environmental standpoint, they should be nearly, or completely blind, but they definitely aren't. This may be the aide of technology at play, or this could just be part of their natural evolution, as contradictory to their environment as it may be.
- They have weapons. And they have used them on humans countless times. Most recently, 14 sailors were killed while onboard a very mysterious, deep-diving nuclear Russian submarine called the Losharik. This is no ordinary submarine by any means, and why they were operating off the coast of Norway is unknown, as are most things involving Russia. This sub is specially designed for deep-diving. Really deep diving. Like 10 times as deep as the typical American crewed submarine (20,000+ ft).
This is significant, because it was not believed that manned submarines went that deep, American ones certainly do not. So it seems, in the water at least, Russia has us beat in some ways. More on topic, Russia has a particular interest in these beings, and has tried to establish contact with them multiple times over the years. I'm sure I mentioned it above, but Russia encountered them first, under lake Baikal, in Siberia.
Back to the Losharik. Whatever they were really doing, apparently encroached upon the neighborhood/territory of these aquatic species, and they responded aggressively. The official story that Putin delivered was an electrical fire onboard. Now we would hear about naval disasters all the time obviously, even the ones that we aren't supposed to know about. One thing about the oceans, they are large, difficult to traverse (for us) and a great place to hide things.
Think about this as well... What's at the bottoms of our oceans, mostly criscrossing the floor of the North Atlantic? Endless miles of fiber-optic cables that carry a large fraction of the world's internet traffic, including trillions of dollars in financial transactions. There are also cables linking to the sonar listening devices that litter the ocean floor.
Basically they've likely all the information about us as a species that they need. We don't know if either of these civilizations ever plan to integrate with life on the surface, and given how long they've been where they are it seems unlikely. Btw... These are just two species that I'm personally aware of through my tenure. I've heard stories of about a dozen others, mostly non-terrestrial. I've heard RUMORS that there are upwards of 60 species that have/do occupy/visit the earth, but I'm only speaking on data and evidence I've seen personally.
Various species definitely makes sense. It would explain why UFO/USO craft, and the description of their occupants varies so greatly over history. Saucers, tictacs, orbs, cubes, triangles, and countless other forms are still reported daily. Even underwater, the craft we are aware differ drastically. I've seen typical, nondescript egg shapes, perfectly round metallic orbs, and even flat, disk shaped craft. All seemingly unaffected by gravity, the water itself, and pressure. They don't seem to splash or disturb water when making contact. We have no idea how that's possible within our understanding of physics.
So there's a lot that we do know, and a lot that we don't. Whether you believe any of this or not is up to you. I was pointed here by a close friend that I've shared this information with recently.