Most of Earth remains poorly explored, and the answer depends on what you mean by “discovered.” Roughly 71% of the ocean floor has never been directly mapped with modern instruments. Somewhere around 86% of the planet’s plant and animal species have not yet been formally described by science. Entire mountain ranges sit buried beneath Antarctic ice, and continent-sized structures deep in the mantle are still only vaguely understood. The question is less “how much is undiscovered” and more “which parts, and why.”
The Ocean Floor
The seafloor is the most obvious gap in our knowledge of Earth’s physical surface. As of 2024, directly mapped area had reached about 28.5%, with the bulk of that work done using multibeam echo sounders that bounce sound waves off the bottom to build detailed depth maps.1Frontiers in Marine Science. Status of global seafloor mapping effort and priority areas for future mapping That means more than 70% of the ocean floor has only been characterized by satellite-derived gravity data, which gives you a rough outline of major features but misses anything smaller than a few kilometers across. Seamounts, fault scarps, hydrothermal fields, and submarine canyons can all hide in those gaps.
The problem is sheer scale. The ocean covers about 361 million square kilometers, and mapping it with ship-mounted sonar is slow and expensive. A single research vessel might survey a few thousand square kilometers per day under good conditions. The Seabed 2030 initiative, which aims to map the entire ocean floor by decade’s end, has made real progress, but the pace of new coverage would need to accelerate dramatically to hit that target. Polar waters present additional challenges: ice cover limits ship access, and the geometry beneath ice shelves is especially hard to reach.
Antarctica’s continental shelf is a case in point. Researchers have recently used gravity-anomaly inversions to model the bathymetry beneath ice shelves, revealing previously unknown deep troughs that could allow warm ocean water to reach glacier grounding lines.2Scientific Reports. Bathymetry of the Antarctic continental shelf and ice shelf cavities from circumpolar gravity anomalies and other data Under the Filchner-Ronne Ice Shelf, new seismic measurements have uncovered a sill between Berkner Island and the mainland that could redirect ocean circulation in the cavity, along with deep troughs near glacier grounding lines that weren’t in previous charts.3Journal of Geophysical Research: Oceans. A New Bathymetry for the Southeastern Filchner‐Ronne Ice Shelf: Implications for Modern Oceanographic Processes and Glacial History These aren’t minor details. The depth and shape of cavities beneath ice shelves directly affects how fast glaciers melt and, by extension, sea-level projections. The fact that we’re still finding major features under Antarctic ice in the 2020s says a lot about how incomplete our picture of the seafloor remains.
Species We Have Not Yet Named
If “undiscovered” means species that science hasn’t described, the numbers are staggering. One widely cited estimate predicts roughly 8.7 million eukaryotic species on Earth, of which about 86% have not been formally described. In the ocean, the proportion is even higher, at around 91%.4PLOS Biology. How Many Species Are There on Earth and in the Ocean? That figure covers complex organisms like animals, plants, and fungi. It does not include bacteria, archaea, or viruses, where the unknowns are vastly larger still.
Where are all these missing species? Many are insects in tropical forests, particularly canopy-dwelling beetles and other small arthropods that live in hard-to-reach microhabitats. One study of Australian tropical rainforest bark beetles found that sampling additional locations and canopy layers yielded new species more effectively than switching collection methods, suggesting the issue is geographic coverage, not technique.5Insect Conservation and Diversity. What can an analysis of Australian tropical rainforest bark beetles suggest about the missing millions of Earth’s insect species? Others are nematodes and other tiny invertebrates in deep-sea sediments. In the deep Mediterranean alone, researchers estimate that about 66% of species (excluding bacteria) remain undiscovered, with nematode worms likely the largest group of unknowns.6PLOS ONE. Deep-Sea Biodiversity in the Mediterranean Sea: The Known, the Unknown, and the Unknowable
An important nuance: the deep sea is not necessarily the richest frontier for new species. Species diversity actually tends to be lower in the deep ocean than on continental shelves, because the deep-sea floor is relatively uniform. Deep-sea species tend to have large geographic ranges and good dispersal ability, which means fewer species overall but spread across enormous areas.7Current Biology. Marine Biodiversity, Biogeography, Deep-Sea Gradients, and Conservation Coral reefs and tropical coastal waters likely harbor a higher concentration of undescribed species per square kilometer than the abyssal plains do. The deep sea’s advantage is size: it covers so much territory that even low per-area diversity adds up to many unknown species in absolute terms.
The Microbial Majority
When you move from animals and plants to microbes, the word “undiscovered” takes on a different meaning. Scientists have a name for the problem: microbial dark matter. In most environments, only somewhere between 0.1% and 1% of microorganisms have been successfully grown in lab cultures, which historically was the main way new species were identified.8PubMed. The bright side of microbial dark matter: lessons learned from the uncultivated majority Genetic sequencing has opened a window into this invisible world, but even with modern DNA-based methods, a large fraction of what turns up is unrecognizable.
In ocean surveys, almost half of the eukaryotic gene sequences recovered from global sampling expeditions showed no similarity to any known protein.9Nature Communications. A global ocean atlas of eukaryotic genes Across a range of habitats, between a quarter and just over a third of unique microbial taxa found in a given environment could not be matched to anything in existing catalogs.10The ISME Journal. A network approach to elucidate and prioritize microbial dark matter in microbial communities Soil, which sits right under our feet, is particularly rich in unknowns. A large-scale genomic analysis of soil samples found that about 78% of the bacterial and archaeal groups recovered were previously uncharacterized.11PubMed Central. A genomic catalogue of soil microbiomes boosts mining of biodiversity and genetic resources
This isn’t a matter of failing to look. Even the Tara Oceans expedition, which sampled 210 ocean stations worldwide and generated a microbial gene catalog of over 40 million entries, only scratched the surface of oceanic microbial diversity.12Scientific Data. Viral to metazoan marine plankton nucleotide sequences from the Tara Oceans expedition The challenge is that microbes evolve fast, occupy every conceivable niche, and many cannot survive outside their native conditions. You can sequence their DNA from environmental samples, but understanding what they do and how they fit into ecosystems is a separate, slower process.
Hydrothermal Vents and the Deep-Sea Floor
Hydrothermal vents are among the most dramatic habitats on Earth, supporting entire food webs in total darkness through chemical energy. Yet we have found only a fraction of them. A global estimate based on the relationship between vent-field frequency and the rate at which tectonic plates spread apart suggests that roughly 900 vent fields on oceanic spreading ridges remain undiscovered. That’s comparable to the total number found during 35 years of searching. Nearly half of the missing ones are predicted to lie along slow-spreading ridges, where the vents tend to be farther apart and harder to locate.13Deep Sea Research Part II: Topical Studies in Oceanography. Where are the undiscovered hydrothermal vents on oceanic spreading ridges
Each undiscovered vent field potentially harbors species that live nowhere else. Vent ecosystems are often isolated from one another by hundreds of kilometers of barren seafloor, which means individual fields can develop unique communities over time. Finding them matters for more than just biological cataloging. Vent fields are of interest to deep-sea mining companies looking for metal-rich sulfide deposits, and conservation decisions about which areas to protect are hard to make when you don’t know where half the vents are.
Under the Antarctic Ice Sheet
Antarctica hides an entire landscape that, for most practical purposes, is undiscovered terrain. Ice several kilometers thick covers a continent roughly the size of Australia and Europe combined. We know from radar and seismic surveys that mountain ranges, deep valleys, and what appear to be river-carved features lie beneath the ice. A recent satellite-derived elevation map of Antarctica’s subglacial topography captured previously unresolved features at scales of 2 to 30 kilometers, revealing patterns of roughness and geomorphology that had been invisible in older models.14PubMed. Complex mesoscale landscapes beneath Antarctica mapped from space
The Gamburtsev Subglacial Mountains, buried deep beneath East Antarctica, have an alpine-style topography that has been pieced together from ice-surface morphology rather than direct observation of the rock itself. The landscape beneath the ice controls where basal melting happens, how subglacial water flows, and how stable the ice sheet is over long time scales.15The Cryosphere. Alpine topography of the Gamburtsev Subglacial Mountains, Antarctica, mapped from ice sheet surface morphology It also shapes the search for “oldest ice,” cores of ancient ice that could contain climate records going back millions of years.
Subglacial lakes are another notable feature. Hundreds have been identified from radar surveys, and geostatistical modeling has been used to estimate their total distribution across the continent, though results suggest some earlier predictions overestimated their extent.16Journal of Geophysical Research: Earth Surface. Antarctic Topographic Realizations and Geostatistical Modeling Used to Map Subglacial Lakes These lakes, sealed from the atmosphere for potentially millions of years, are targets for astrobiological research. If life persists in them, it would tell us something about the limits of biology in extreme isolation.
Earth’s Deep Interior
The most inaccessible part of the planet is directly below you. The deepest borehole ever drilled barely reached 12 kilometers, about 0.2% of the way to Earth’s center. Everything we know about the mantle and core comes from indirect methods, mostly from the way seismic waves from earthquakes bend and slow as they pass through different materials.
Two of the most mysterious structures in the deep Earth are the large low-velocity provinces, or LLVPs, which sit in the lower mantle beneath Africa and the Pacific Ocean. These are continent-sized zones where seismic waves slow down, indicating material that differs from the surrounding mantle in composition, temperature, or both.17Scientific Reports. Unique composition and evolutionary histories of large low velocity provinces They are nearly antipodal, sitting roughly on opposite sides of the planet, and likely represent chemically distinct, denser material.18PubMed. Structure and dynamics of Earth’s lower mantle Their origin is debated. Some researchers think they formed from subducted oceanic crust that accumulated over billions of years. Others propose they are primordial material left over from Earth’s formation. Neither idea is settled.
Water stored in the mantle is another frontier. The mantle transition zone, a layer stretching from about 410 to 660 kilometers deep, may hold the equivalent of between 0.2 and one full ocean’s worth of water, locked into the crystal structures of high-pressure minerals.19Oxford Academic (National Science Review). The role of water in Earth’s mantle The lower mantle could hold even more, though estimates there are poorly constrained. This water isn’t liquid; it’s bonded at the atomic level into rocks. But its presence affects how the mantle flows, how volcanoes erupt, and how plate tectonics operates. The idea that there may be more water inside Earth than in all the surface oceans is still being tested, and the deep mantle remains one of the most uncertain parts of the picture.
Life Underground
The deep terrestrial biosphere, the ecosystem of microbes living in rock and groundwater far below the surface, is a relatively recent scientific discovery. Organisms have been found thriving at depths of several kilometers, surviving on chemical energy from rock-water reactions rather than sunlight. Analysis of subsurface groundwater samples from four continents has identified core microbial populations that appear globally, suggesting a connected deep biosphere with its own characteristic community structure.20PubMed Central. A global deep terrestrial biosphere core microbiome
The total biomass of subsurface life is thought to be a substantial fraction of all life on Earth, but estimates keep shifting as sampling improves. Only a tiny number of sites have been drilled deeply enough to collect biological samples, and most of those are in places where boreholes were sunk for mining, oil, or geological research, not for biological exploration. The gap between where we’ve looked and where life could exist is enormous.
Even the water itself underground holds surprises. Offshore freshened groundwater, pockets of fresh or brackish water trapped in sediments beneath the continental shelves, has a global estimated volume of about one million cubic kilometers. It mostly sits within 55 kilometers of the coast and down to about 100 meters of water depth, and was recharged by rainwater during ice-age sea-level lows when those shelves were dry land.21Reviews of Geophysics. Offshore Freshened Groundwater in Continental Margins In a world increasingly stressed for freshwater, this resource is largely unmapped and barely tapped.
Caves and Subterranean Biodiversity
Caves are among the least explored habitats on land. They host specialized species, many of them blind, unpigmented, and found nowhere else, that have adapted to permanent darkness over millions of years. Cataloging cave-restricted species is painstaking work: researchers physically enter each cave, often crawling through tight passages, and systematically collect specimens. A global assessment identified at least 26 subterranean biodiversity hotspots, defined as sites with 20 or more cave-restricted aquatic or terrestrial species.22Oxford Academic. Patterns and Drivers of Subterranean Biodiversity Hotspots across the Globe The actual number of hotspot caves is certainly higher because vast karst regions in tropical Asia, Africa, and South America have barely been surveyed for cave fauna.
Cave species are acutely vulnerable to disturbance. A single cave system might be the entire world range of a dozen species. Pollution, changes in water flow, or even heavy foot traffic from tourism can devastate a community that took millions of years to evolve. The paradox is that conservation depends on knowing what’s there, and for most of the world’s caves, nobody has checked.
Hidden Archaeology Beneath the Canopy
Undiscovered Earth also includes the human past. Dense tropical vegetation has concealed entire civilizations from ground-based survey. Lidar, which fires millions of laser pulses from aircraft or drones and builds three-dimensional surface models by measuring their reflections, has transformed archaeology in forested regions. The technology can “see through” tree canopy to reveal earthworks, roads, water-management infrastructure, and settlement platforms that are invisible at ground level.
In the Bolivian Amazon, lidar documented two large settlement sites along with 24 smaller ones, of which only 15 had been previously known. The survey revealed a four-tiered settlement hierarchy with civic-ceremonial architecture, straight causeways, canals, and water reservoirs, indicating organized low-density urbanism that predated European contact by centuries.23Nature. Lidar reveals pre-Hispanic low-density urbanism in the Bolivian Amazon Discoveries like these have rewritten assumptions about how many people lived in tropical lowlands and how complex their societies were. Lidar has made similar finds in Central America, Southeast Asia, and West Africa, uncovering lost cities, agricultural terraces, and defensive structures.24Jurnal Ilmu Pendidikan dan Humaniora. Unveiling the Past: LiDAR Technology’s Role in Discovering Hidden Ar-chaeological Sites Most tropical forests have not yet been surveyed with lidar, so the archaeological map of the world is still filling in rapidly.
How Much Wilderness Is Left
One way to flip the question is to ask how much of Earth’s land surface is still relatively untouched by human activity, places where there’s genuinely uncharted territory in a biological or ecological sense. As of 2013, about 42% of Earth’s land surface was classified as “intact” with a low human footprint. A smaller subset, about 25%, qualified as wilderness with virtually no human pressure.25One Earth. Annual Changes in Global Terrestrial Human Footprint and Assessing Ecosystem Degradation The remaining 58% was under moderate or intense human pressure, spanning over half the area of 11 out of 14 biomes. Those intact and wilderness areas, concentrated in boreal forests, tundra, deserts, and the Amazon basin, are where undiscovered terrestrial species and ecosystems are most likely to be hiding. They are also shrinking year by year.
Microbes in the Stratosphere
Even the sky has an undiscovered frontier. Viable bacteria have been recovered from Earth’s stratosphere, at altitudes up to 26 kilometers, well above the zone where weather happens. Samples collected by high-altitude balloons and NASA research aircraft have yielded isolates from multiple bacterial groups, some of which showed extreme tolerance to desiccation and ultraviolet radiation, with UV survival rates comparable to the famously radiation-resistant bacterium Deinococcus radiodurans.26The ISME Journal. Abundance and survival of microbial aerosols in the troposphere and stratosphere Separate balloon experiments with environmental samples confirmed that cultivation from stratospheric-exposed material was possible, with survival rates of at least 1%.27PubMed Central. Flying microbes-survival in the extreme conditions of the stratosphere during a stratospheric balloon flight experiment
The bacterial communities found at flight altitude resemble those in the lower atmosphere, suggesting that what’s up there got lofted from the surface rather than evolving in place.28PubMed Central. Airborne Bacteria in Earth’s Lower Stratosphere Resemble Taxa Detected in the Troposphere: Results From a New NASA Aircraft Bioaerosol Collector (ABC) But whether any of these organisms actually metabolize and reproduce at altitude, as opposed to merely surviving transit, is still unclear. The stratosphere remains one of the least sampled environments on Earth, and its microbial ecology is almost entirely terra incognita. The implications reach beyond Earth: if life can endure stratospheric conditions, similar organisms could theoretically survive in the upper atmospheres of other planets, a question that drives some of the interest in this research.