The question of what percentage of Earth has been explored has no single, simple answer because the word “explored” has multiple definitions depending on the domain being measured. Exploration can mean basic surface mapping, the physical presence of a human, or the comprehensive scientific survey of biological and geological features. While Earth’s surface is known, the planet’s vast oceans and subterranean regions remain largely unknown. Understanding the exploration status of our world requires breaking down the planet into its distinct components and applying different measures of discovery to each one.
Establishing the Metrics of Exploration
The perceived percentage of Earth explored changes dramatically based on the required level of detail. If “explored” is defined as basic cartographic knowledge—meaning the surface has been remotely sensed and mapped—the planet is nearly 100% explored. Satellite technology has provided a foundational image of almost every square meter of the surface, establishing the general topography of continents and the shape of the ocean floor. This high percentage plummets when the definition shifts to comprehensive scientific exploration.
A more rigorous definition requires physical presence, detailed biological inventories, and deep geological sampling. Under this standard, which accounts for the composition of the environment and the life it holds, the Earth is far less than fully known. For instance, a satellite can map a forest canopy, but it cannot catalogue the microscopic life in the soil or the biodiversity within the trees. Therefore, a figure representing detailed scientific exploration would be significantly lower, likely less than 20% of the planet’s total volume.
Terrestrial and Cartographic Assessment
The exploration status of the Earth’s landmass is overwhelmingly complete in terms of surface mapping. High-resolution satellite imagery and remote sensing technologies, like LiDAR, have produced digital elevation models and visual maps covering over 97% of the globe. These tools allow for the observation of surface features with resolutions as fine as 0.3 to 15 meters per pixel in many areas, providing nearly total cartographic coverage of the continents.
Even in isolated land regions, such as parts of the Amazonian rainforest, remote polar ice fields, or arid deserts, the basic contour and vegetation cover are known. The remaining gaps in terrestrial knowledge are often confined to specialized environments, like deep cave systems that branch far beyond human access. While the land surface is mapped, the comprehensive biological and geological surveying of these landscapes is an ongoing process that still requires extensive fieldwork.
The Vastness of the Deep Sea
The ocean represents the largest domain of the planet that remains fundamentally unexplored, covering over 70% of the Earth’s surface. A primary metric for ocean exploration is bathymetry, the measurement of the seafloor’s depth and topography. Only slightly more than 23% of the ocean floor has been mapped with high-resolution sonar technology, such as multibeam echo sounders.
This means that nearly 77% of the abyssal plains, oceanic trenches, and underwater mountain ranges are known only through low-resolution satellite data that estimates depth by measuring gravitational variations on the sea surface. An international effort, the Nippon Foundation-GEBCO Seabed 2030 Project, aims to achieve 100% high-resolution mapping of the ocean floor by the year 2030. The process is slow and costly; it has been estimated that a single ship would require nearly 1,000 years to map the entire ocean basin.
Beyond mapping the topography, biological and physical exploration of the deep ocean is even more limited. The extreme pressure, complete lack of light, and frigid temperatures make direct exploration incredibly difficult. While remotely operated vehicles (ROVs) and human-occupied submersibles have visited various deep-sea ecosystems, vast expanses of the water column and the deep ocean floor have never been observed directly. For example, the deepest point in the ocean, the Challenger Deep, has only been visited by a handful of expeditions.
Subterranean and Deep Crust Unknowns
The exploration of the Earth beneath its surface is severely restricted by mechanical and thermal limitations. The solid crust, which is the planet’s outermost layer, extends for tens of kilometers, but human physical penetration is measured in mere kilometers. The most ambitious drilling project ever undertaken, the Kola Superdeep Borehole in Russia, reached a maximum depth of 12,262 meters, or about 7.6 miles.
This depth represents only about one-third of the estimated thickness of the continental crust in that region, which is a fraction of the distance to the mantle below. Despite this limited penetration, scientific drilling has revealed a largely unexplored region known as the deep biosphere. This subterranean zone of life, which exists within the pores and cracks of the rock, is estimated to have a volume approximately twice that of all the world’s oceans.
Microbial life has been sampled at depths of up to five kilometers in the continental crust and 10.5 kilometers below the ocean floor, surviving in extreme conditions without sunlight. This hidden world of bacteria and archaea represents a massive portion of Earth’s total biomass and diversity. The physical and biological exploration of this deep, hot biosphere is arguably the least explored domain on the entire planet.