Stony corals form a type of calcium carbonate called aragonite from ions brought to the ocean by rivers that have broken down terrestrial rocks.

Coral reefs are built by thousands of coral polyps—tiny animals whose mouths both consume food and expel waste.

Watch a time-lapse of staghorn coral polyps—a type of hard coral—over several weeks in an aquarium, slowly forming the foundational component of a coral reef.

The first coral reefs formed hundreds of millions of years ago from the carbonate skeletons deposited by hard corals.

The three types of coral reefs—fringing, barrier, and atoll—are categorized by where they form.

Deep water corals—located throughout the world's ocean basins at depths beyond 200 meters (660 feet)—slowly build small coral gardens in the dark with the help of underwater worms.

Coral reefs get their colors from zooxanthellae—microorganisms that line corals' digestive tracts and provide them with sugars in exchange for a home within this protective tissue.

Artificial coral reefs have been 3D printed from nontoxic, biodegradable terracotta clay, which coral polyps have used as a foundation for rebuilding marine ecosystems.

An analysis of fossilized reefs from northern Africa and Germany suggests that shallow water corals and photosynthetic algae formed the mutualistic partnership seen today between 419 and 359 million years ago.

Over 1 million fish, marine mammals, and invertebrate species depend on coral reefs for habitats, camouflage, and food.

As immobile animals, corals and the organisms that live on them have evolved a suite of chemical compounds to prevent disease and ward off predators they cannot outrun.

Niagara’s bedrock holds 440-million-year-old coral fossils

The Lockport Dolomite that caps Niagara Falls is composed of fossilized coral reefs from a tropical sea that once covered the region 440 million years ago.

Through coral IVF, researchers have collected coral eggs and sperm from healthy reefs, grown baby corals in lab pools, and then released them to help repopulate damaged or lost reefs.

Coral polyps reproduce via broadcast spawning, where entire reefs simultaneously release reproductive cells for about one hour, once a year.

Climate change threatens coral reefs by disrupting the symbiotic relationship between corals and algae due to rising ocean temperatures.

Synthetic pheromones may protect coral reefs by attracting their predators

Researchers in Australia and Japan have developed these nontoxic chemicals to attract crown-of-thorns starfish, which consume corals that make up the Great Barrier Reef. As of 2026, synthetic pheromones have been shown to be effective in lab trials, and future field trials will attempt to lure starfish into areas for mass removal.

Overview: All about coral reefs

Coral reefs aren’t just vibrant underwater landscapes; they are also some of the most biologically diverse ecosystems on Earth. The National Oceanic and Atmospheric Administration (NOAA) offers a comprehensive guide that explores coral reefs in...

Fossils form in environments where dead organisms can be rapidly buried

Such landscapes enable corpses to be encased by terrain before significant decay occurs. They are most commonly found in river deltas and sinking coastal regions, where sediments accumulate over time until geological forces expose the areas to erosion, revealing embedded fossils.

Speleothems are diverse mineral formations that form in air-filled caves

Speleothems like stalactites and stalagmites form when water deposits minerals after a cave rises above the water table and fills with air. These formations preserve the mineral deposits, which may serve as climate proxies, for as long as a million years.

Geode formation begins with trapped gas bubbles in igneous or sedimentary rock

Over thousands or millions of years, water seeps into the cavity created by the bubble and deposits minerals, which slowly build and crystallize into quartz, agate, amethyst or other crystals.

View a collection of glass sculptures of corals threatened by fishing and deep-sea mining.

When diving and snorkeling in environments containing reefs, avoid touching reefs, anchoring on them, or using sunscreen with active ingredients harmful to marine life.

Roman concrete lasts longer than modern recipes—and even gets stronger

Today's concrete is made by binding ingredients, including chalk and silica sand, at high temperatures. Unfortunately, it weakens when exposed to salt water. This article explores how and why scientists are studying ancient Roman concrete, which grows stronger when exposed to salt water.

Deep sea fish rely on a molecular strengthener to prevent being crushed

Trimethylamine N-oxide (TMAO) stabilizes hydrogen bonds and prevents water and proteins within organisms from being misshapen under immense pressure. Compounds called piezolytes protect cellular membranes from being crushed in regions like the Mariana Trench, where pressures are 1,100 times greater than surface atmospheric pressure.

Gastroliths, or ‘stomach stones,’ help animals digest plants in their stomachs

Most often used by birds and reptiles, gastroliths help break down the cellulose of plant cells, which can resist decomposition from stomach acid alone. Over time, gastroliths become smooth and are regurgitated before being replaced by larger stones.

Asteroids are artifacts of water's presence in the solar system

Asteroids contributed to planet formation and carried water from the solar system's outer reaches toward the center. They were also early providers of the necessary elements and conditions for life to evolve on Earth.

Layers in sediment cores hold clues to Earth’s past climate

By analyzing materials such as pollen and algae within the layers of these cores, which are collected from lakes and oceans, scientists can learn what the environment and climate were like when that layer formed.

Volcanic activity can lead to the formation of fertile soils

Ejected rock can introduce key minerals found in fertilizers, including iron, magnesium, and potassium, to improve soil quality. Ash and basalt crystals can be easily absorbed into soils, infusing them with sulfur, oxygen, chlorine, phosphorus, calcium, and other critical elements.

Decommissioned oil rigs have been repurposed into artificial reefs that serve as nursery habitats for fish, corals, sponges, and other invertebrates in the decades since their installation.

Minerals, crystals, rocks, and gems explained

Have you ever wondered what differentiates a mineral from a rock or a crystal from a gem? This three-minute video from the American Museum of Natural History elaborates on the unique properties and compositions that separate minerals, rocks,...

Water is naturally tinted with a slight blue, but sediments and organics can alter its color

The innate coloration comes from water absorbing red light in the visible spectrum more than green or blue, giving shallow waters in some parts of the Caribbean their turquoise hue. If sand is light, it can be churned up by turbulent water, clouding its appearance. Plankton and other organisms can color water by affecting how the rest of the spectrum is absorbed or reflected.

'Coral Castle,' Florida's self-built monument to a lost valentine

Latvian Ed Leedskalnin moved to the US shortly after his teenage fiancée ditched him. He quickly began work building a romantic tribute to this tragic episode via massive oolitic limestone. Working mostly at night, the Latvian cultivated an air of mystique as bystanders grew curious over his methods. Today, the castle stands as a bittersweet monument to unrequited love.

Learn about endoliths, the polyextremophiles that thrive inside rocks

These organisms include species that live in Antarctica, where they perform photosynthesis using light and water that makes it through pores in sandstone. Others residing in Earth's crust can survive temperatures reaching 60 degrees Celsius (140 degrees Fahrenheit) while generating energy through chemical reactions involving nutrients and gases trapped in rocks.

38 thought-provoking facts about the ocean

Coral produces its own sunscreen, tsunamis move at 500 miles per hour, one of the loudest sounds ever recorded came from an ice quake, and other interesting facts collected from sources such as National Geographic and NASA.

The Southern Ocean's powerful circular current isolates organisms in its environment

The spiralling current churns up nutrients across the frigid waters, leading to the evolution of fantastical organisms, including century-old starfish and colossal squid, and unique adaptations, including the icefish's clear blood and organic antifreeze, over the past 30 million years.

Salt is harvested from briny ocean water and underground deposits

Mostly sodium chloride, this compound is produced for human use by collecting seawater in shallow pans and allowing the Sun to evaporate the water until crystals remain. Underground rock salt is mined, crushed, and purified from deposits left behind by ancient seas that have dried-up.

Multiple species exhibit convergent evolution by developing crab-like features

Various organisms that appear to be different types of crabs, such as porcelain crabs and coconut crabs, have been shown to belong to distinct decapod lineages whose predecessors resemble shrimp or lobsters. Environmental pressures and other factors have caused these species to develop similar characteristics, which nature has shown are beneficial to survival.

Weird ways critical minerals are being mined

Critical minerals like lithium, cobalt, and graphite are economically crucial non-fuel resources subject to supply chain risks. To diversify production, scientists developed odd ways to harvest them. This article breaks down the weirdest approaches, including extracting minerals from seawater using algae, phytomining plants, and asteroids.

View a map of the distribution of mineral resources on the seafloor

Polymetallic nodules are found in regions near the middle of the Pacific Ocean, along the eastern coast of South America, and along the western coast of Africa, while cobalt-rich crusts span significant portions of the Pacific tropics east of the Philippines. Polymetallic sulfide deposits occur at tectonic plate boundaries, including areas within national jurisdictions.

Scientists discover what looks like an underwater road

Crew aboard the Exploration Vessel Nautilus discvered a “yellow brick road” that looks it leads to Atlantis. Climage change may affect future ocean studies.

Gladiators followed a mostly vegetarian, high-calcium diet

Analysis of skeletons from a gladiator cemetery at Ephesus by researchers at the Medical University of Vienna found little meat consumption but unusually high calcium levels—likely from drinking wood ash mixed with water to promote weight gain and protect vital organs.

Turning some invasive species into cash crops has helped control their spread

In Mexico, some companies are transforming sargassum seaweed blooms into paper, bricks, and shoes, while in Cambodia, water hyacinths are dried and woven into baskets, rugs, and other crafts. Lionfish and green crabs have been hunted for culinary dishes, with the latter also being used to make crab whiskey in New England.

Exposed concrete led to oxygen depletion within Biosphere 2

Instead of being absorbed by plants through photosynthesis to produce oxygen, significant amounts of carbon dioxide were taken up by the calcium hydroxide in the concrete, trapping the oxygen in calcium carbonate and water. This concrete was sealed before the start of the second B2 mission.

How Oceans were formed

Nonprofit organization American Oceans briefly explains the formation of the oceans, which cover over two thirds of Earth’s surface. They were formed by centuries of rain from the condensation of Earth's original gasses.

Underwater volcanoes significantly contributes to marine extinctions during the Triassic period

An analysis of ocean basins in the Tibetan Plateau helped identify three major periods of volcanism—250-248, 233-231, and 210-208 million years ago—which released significant amounts of greenhouse gases, altering ocean chemistry. The low-oxygen conditions may help explain half of Earth's Triassic extinctions.

Slab pull and ridge push contribute to convection-driven oceanic crust movement

Through ridge push, after magma is projected up from the mantle, it cools and sinks, allowing gravity to help push older oceanic crust away. As this crust sinks into the mantle at deep-sea trenches, it pulls on the trailing crust behind it, accelerating ocean crust movement.

Iron rusts in the presence of water and oxygen because these ingredients enable the metal atoms to release energy and enter a more stable state.

When caught in the mouths of cardinal fish, seed shrimp release glowing, bioluminescent chemicals, which alert predators of the cardinal fish, prompting the shrimp's ejection.

The ratio of stable carbon isotopes in climate proxies provides climate variable data

Measures of the abundance of carbon-13 and carbon-12 can vary in a sample due to environmental and climatic factors. Plants more readily assimilate carbon-12 during photosynthesis, allowing the ratio to serve as a proxy for past conditions that favored plant life.

How chemical bonds between atoms form molecules and large geometric structures

In ionic bonding, one atom transfers at least one electron to another atom, forming two atoms of opposite charge. These atoms attract one another and can stack up in a 3D grid called a lattice. Covalent bonding, where electrons are instead shared, can produce enormous molecules, such as the two found in human chromosome 13, which each contain 37 billion atoms.

Santa Barbara's Channel Islands revealed the oldest skeletal remains in North America

IN 1959, archaeologists found a human femur jutting out from a rock face on Santa Rosa Island. Using the then-new technology of radiocarbon dating, they measured the age of the remains at 13,000 years—the oldest in the continent.