How we know what’s deep inside the Earth, despite never traveling there

Scientists investigate Earth's interior by studying seismic waves

Scientists investigate Earth's interior by studying seismic wavesBelow Earth's atmosphere lies the crust, which extends to the Mohorovičić discontinuity between five and 20 miles below Earth's surface. Below the crust lies the mantle, the liquid-metal outer core, and the solid inner core, which surpasses 5,200 degrees Celsius (9,392 degrees Fahrenheit).

Earth's inner structure is a dynamic system of layers in constant, slow motion

From the crust to the core, each of Earth's layers—some solid, some liquid—plays a role in generating its magnetic field, moving tectonic plates, and cycling matter. These details are determined through modeling since humans have only drilled 12 kilometers underground.

As of 2025, humans have only dug 0.2% the way to Earth's center

The Kola Superdeep Borehole revealed two billion-year-old fossils and underground water, but the immense temperature and pressure prevented further tunneling. Beyond those depths, scientists know of Earth's interior by analyzing how seismic waves move.

Take a journey to the Earth's core

This animated video takes you on a journey through the different layers of the Earth's core, with insight into what makes up each shell. Earth's outer core, which is about 1,400 miles thick, is made up of liquid iron and nickel at a blistering...

Heat slowly moves through Earth's mantle like softened wax

Energy trapped during Earth's formation and released via the radioactivity of elements is carried by convection currents towards the surface, while cooler, denser material sinks. The planet's core is almost as hot as the sun's surface.

Earth's core is leaking precious metals, including gold

Earth's core, containing 99.999% of all known gold, is leaking trace amounts of precious metals into the mantle. Advanced isotopic methods have detected this leakage at volcanoes in Hawai'i, providing new insights into the movement of material beneath Earth's surface.

View the internal structure of the sun and its puzzling surrounding atmosphere

From the stellar core to the surface, the sun's density decreases from more than 10 times that of lead to 0.00001% that of air, while temperatures drop from millions to thousands. Temperatures increase from the sun's surface to the outermost layer of its atmosphere—the corona—a phenomenon whose explanation is still under investigation.

Variations in rock types contribute to uncertainty in earthquake predictions

Different rock types can withstand different amounts of stress before breaking and melt at different temperatures within Earth’s interior, preventing uniform modeling. The planet’s uneven mass distribution also creates variations in gravitational force, complicating mantle movement.

Explore the deepest parts of the ocean

The deeps of the Earth's oceans are some of the most extreme environments on the planet. Take a trip 36,000 feet to the deepest parts of the sea in this informative, 10-minute animated video.

How diamonds form in the deep earth

Deep within Earth's mantle, diamonds form from carbon-bearing fluids. The formation of these beautiful gemstones, the only direct samples we have of the mantle, helps scientists uncover how carbon functions deep inside our planet. Understanding this complex process aids in the exploration for new diamond deposits.

What makes the Earth shake?

Researchers are demystifying the science of earthquakes—from their origins deep within the Earth to the scales that measure their strength. This article, which was part of a series of weekly reports from Cornell University, serves as a guide to...

How neutron stars resemble Earth, including harboring an atmosphere and 'mountains'

These stars maintain an atmosphere of hydrogen, helium, and carbon at approximately 2,000,000 degrees Celsius (3,600,000 degrees Fahrenheit), only a few thousandths of a millimeter thick, which envelops "mountains" about a millimeter high. Its interior consists of an inner and an outer crust surrounding inner and outer cores, all held together by enormous gravitational forces despite spinning multiple times a second.

A look at hydrothermal vents, where barophiles and hyperthermophiles survive boiling water

Discovered in 1977 during an exploration of the Galapagos Rift, these seafloor openings spew hot magma and chemicals that heat seawater to hundreds of degrees. Without the sunlight found at depths of less than 1,000 meters (3,281 feet), extremophiles in these environments convert released chemicals into energy to survive, alongside surviving extreme pressures.

Travel through deep time with this interactive Earth

Explore key moments in Earth’s transformative history as continents drift and climate fluctuates over 4.6 billion years. The Smithsonian presents a series of interactive snapshots of the earth. From its toddler years during the Hadean period, when its surface was mostly molten, to the mostly unidentifiable landmasses of the future earth, 100 million years from now.

Earth's core is about 2.5 years younger than its surface according to relativity

Due to differences in where objects are located within gravitational fields, time will run at different rates, which has major impacts on technology that relies on synchronization. For example, GPS satellites run about 38 microseconds faster every day than clocks on Earth's surface, resulting in GPS discrepancies of about six miles, were it not for software corrections.

Explosive volcanic eruptions happen when magma pressure overcomes rock strength

Magma usually stays underground because of a balance between its upward pressure, the weight of the Earth’s crust above, and the crust’s rock strength. Landslides can reduce crust weight, while built-up gas pressure can strengthen magmastatic pressure.

How scientists study Earth's geocorona, the farthest portion of the planet's exosphere

Seen via ultraviolet radiation scattered by neutral hydrogen in the region, observations by the ESA/NASA Solar and Heliospheric Observatory indicate that the geocorona extends roughly 50 times Earth's diameter above its surface. At this distance, the geocorona extends beyond the Moon's orbit.

NASA uses extreme Earth environments to prepare for space exploration

Analog missions in volcanic terrains and craters mimic Martian and lunar environments. Crew members operating in these missions, including at sites in Utah, Nevada, Arizona, and Hawai'i, test suits and specialized space instruments under simulated conditions.

The weight of Earth's atmosphere is equivalent to a 33-foot deep, global ocean

Because air is made up of gas molecules with mass, it is not weightless. On the planet's surface, we are effectively living in what is the equivalent of the bottom of an invisible ocean of these particles pressing against us, just as water molecules do when we are submerged.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

What lies inside a black hole remains one of the universe's greatest mysteries

At the center of black holes is a theoretical point of infinite density called a singularity. Alternatively, one theory suggests a black hole's core could form a Planck star—a mind-bogglingly tiny object just a trillionth trillionth trillionth of a meter in size.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Explore the animals that populate the depths of the ocean, from fish and coral in the first few hundred feet, all the way down to the bottom of the Mariana Trench.

Supermassive black holes create pressure waves, detectable as extremely low sounds

Space is largely silent because it lacks a medium for sound waves. Some Mars rovers capture sounds of wind, though the sounds are too low to hear. Through sonification, astronomical data can be translated into hearable sounds for broader engagement.

An in-depth look at Venus, our gassy neighbor

Get to know Venus, one of our closest planetary neighbors. Despite being named for the Roman goddess of love—and the only one named for a woman—Venus is an searingly hot place covered in thick carbon dioxide clouds, volcanoes, and warped mountain ranges. Yet it has a lot to teach us about planet Earth.

Explore the Earth at night from space

See the planet in all its luminosity with this NightEarth app, an interactive spherical globe showing real satellite imagery of Earth. Toggle between views of real-time clouds, aurora borealis activity, and more.

The hypothetical matter that neutron stars' cores may contain, including strange quarks

Models of the extreme pressures and energies in neutron stars suggest conditions resembling those believed to have existed within a fraction of a second after the Big Bang. In these environments, the quarks that make up protons and neutrons in trios may instead form pairs that combine to form one quantum object. (Some readers may experience a paywall.)

Volcanoes 'die' when their supply of magma runs out, if they are shifted away from their underlying magma reservoir, or if they get clogged by collapsing or their magma cooling back into rock.

Neutron stars, the remains of some massive stars after they explode in a supernova, are the densest directly observable objects in the universe.

Stars appear to twinkle because turbulence in the motion of molecules in Earth's atmosphere causes light to bend and wiggle rapidly on its way to the surface—a phenomenon called scintillation.

According to the physics of black holes, our 4D reality may be a hologram—a projection of information coded on a 2D surface on the edge of the universe.

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

Dirty lightning is a thunderstorm created from friction between rising and falling flows of ash and smoke during volcanic eruptions.

The boiling temperature of water decreases with increasing elevation because the molecules need less energy to overcome the lower atmospheric pressure associated with thinner air.

Track the location of the Voyager probes, currently between 13 and 15 billion miles away from Earth.

See the 25 of the best photos of auroras from around the world.

Explore the archaeological treasures of Pompeii, the city buried under volcanic ash when Mount Vesuvius erupted in 79 CE.

After NASA's Voyager 1 captured Earth as a single pixel as it left the solar system in 1990, astronomer Carl Sagan used the image to reflect on humanity's fragility and the responsibility to protect 'the only world we've ever known.'

Visualize the path of every solar eclipse from 1900 to 2099 and see what each looks like when observed from different locations on Earth.

Massive 3D printers have been used to build homes by stacking layers of 'concrete toothpaste,' a fire-resistant material that effectively insulates against outside noise.

Researchers believe the brain consolidates memories, processes emotions, and plans for the future during dream states

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

How the most famous Ebola book, The Hot Zone, which sold 3.5 million copies and was translated into 30 languages, got aspects of the disease so wrong.

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

SpaceX's S-1 or 'prospectus' revealed many previously unknown details about the company, including its unprofitability despite doing $18.7B in revenue in 2025, exactly how many voting shares Elon Musk will have in the company (roughly 85%), and more.

Existentialist writer Jean-Paul Sartre coined the famous phrase 'Hell is—other people' in his play 'No Exit'

In 2018, 26-year-old missionary John Allen Chau was killed by tribesmen after attempting to reach and evangelize on India's isolated North Sentinel Island

Clever Hans was a 1900s horse that was believed to be able to solve math equations, tell time, and read and comprehend German, until a psychology student discovered how he got his answers.