Reliving the last day of the dinosaurs | Science News for Students

Reliving the last day of the dinosaurs

Geologic sites are telling the story of the asteroid impact that abruptly changed life on Earth
Jun 13, 2019 — 6:45 am EST
an illustration of an asteroid impacting the Earth

A massive asteroid hit the Earth 66 million years ago. The explosive collision rattled the planet and changed its climate. The devastating changes it triggered abruptly wiped out the dinosaurs — and most other living species.

solarseven/iStock/Getty Images Plus

Let’s travel back 66 million years to a balmy day in what is now Texas. A herd of 30-ton alamosaurs graze peacefully in a steamy marsh. Suddenly, a blinding light and a scorching fireball envelops them.

It is the last thing these dinosaurs see.

Fifteen hundred kilometers (900 miles) away, an asteroid moving at 50 times the speed of sound has just slammed into the Gulf of Mexico. The space rock is huge — 12 kilometers (7 miles) wide — and white hot. Its splashdown vaporizes a portion of the Gulf’s water and much of the limestone below.

The aftermath is history: a monstrous crater, major extinctions and the end of dinosaurs. In fact, the impact forever changed the course of life on Earth. With dinosaurs gone, mammals rose to dominate the land. New ecosystems formed. From the ashes, a new world arose.

But what really happened on that very violent, very last day of the Cretaceous (Kreh-TAY-shuus) Period? As scientists peer underground in the Gulf of Mexico and elsewhere, new details are emerging.

Mystery crater

The fossil record clearly shows a major extinction at the end of the Cretaceous. Dinosaurs that had walked the Earth for tens of millions of years vanished suddenly. Why remained a mystery for many years.

Then in the 1980s, geologists noticed a distinct layer of rock in many places around the world. The layer was very thin, generally no more than a few centimeters (several inches) thick. It always occurred at exactly the same place in the geologic record: where the Cretaceous ended and the Paleogene Period began. And everywhere it was found, the layer was packed with the element iridium.

Iridium is extremely rare in Earth rocks. It is, however, common in asteroids.

The iridium-rich layer was all over the Earth. And it appeared at the same moment in geologic time. That suggested that a single, very big asteroid had struck the planet. Bits of that asteroid had flown into the air and traveled around the globe. But if the asteroid was so big, where was the crater?

“Many felt it must be at sea,” says David Kring. “But the location remained a mystery.” Kring is a geologist at the Lunar and Planetary Institute in Houston, Texas. He was part of a team that joined that search for the crater.

Chicxulub map
The Chicxulub crater is now buried partly under the Gulf of Mexico and partly under the Yucatán Peninsula.
Google Maps/UT Jackson School of Geosciences

In about 1990, the team discovered that same iridium-rich layer in the Caribbean nation of Haiti. But here it was thick — a half-meter (1.6-feet) thick. And it held telltale signs of an asteroid impact, such as drops of rock that had melted, then cooled. Minerals in the layer had been shocked — or altered — by sudden, intense pressure. Kring knew the crater must be nearby.

Then an oil company revealed its own odd find. Buried under Mexico’s Yucatán Peninsula was a semicircular rock structure. Years before, the company had drilled into it. They thought it must be a volcano. The oil company let Kring examine the core samples it had collected.

As soon as he studied those samples, Kring knew they had come from a crater made by the asteroid’s impact. It stretched more than 180 kilometers (110 miles) across. Kring’s team named the crater Chicxulub (CHEEK-shuh-loob), after the Mexican town now near an above-ground site at its center.

Into Ground Zero

an image of the Schrodinger Impact Crater on the moon
The Schrodinger Impact Crater on the moon has a peak ring surrounding its center. By studying the peak ring of the Chicxulub crater, scientists hope to learn more about crater formation on other planets and moons.
NASA's Scientific Visualization Studio

In 2016, a new scientific expedition set out to study the 66-million-year-old crater. The team brought a drill rig to the site. They mounted it on a platform that stood on the seafloor. Then they drilled deeply into the seabed.

For the first time, the researchers were targeting a central part of the crater called the peak ring. A peak ring is a circular ridge of crumbled rock inside an impact crater. Up until then, scientists had seen peak rings on other planets and the moon. But the one within Chicxulub is the clearest — and perhaps only — peak ring on Earth.

One of the scientists’ goals was to learn more about how peak rings form. They had plenty of other questions, too. How did the crater form? What happened just after? How quickly did life within it recover?

A scientific expedition in 2016 drilled into the Chicxulub crater to collect rock cores and study what happened during and after impact and formation of the crater.

Sean Gulick helped lead the expedition. As a geophysicist at the University of Texas in Austin, he studies physical properties that shape the Earth.

The expedition drilled more than 850 meters (2,780 feet) into Chicxulub. As the drill spun deeper, it cut a continuous core through the rock layers. (Imagine pushing a drinking straw down through a layer cake. The core collects inside the straw.) When the core emerged, it showed all the rock layers the drill had gone through.

The scientists arranged the core in long boxes. Then they studied every inch of it. For some analyses, they just looked at it very closely, including with microscopes. For others, they used laboratory tools such as chemical and computer analyses. They turned up many interesting details. For example, the scientists found granite that had splashed to the surface from 10 kilometers (6.2 miles) below the Gulf floor.

a photo of a core drilled from the Chicxulub crater
This core drilled from within the Chicxulub crater came from 650 meters (2,130 feet) below the sea floor. It holds a jumble of melted and partially melted rock, ash and debris.

Along with studying the core directly, the team also combined data from the drill core with simulations that it made using a computer model. With these, they reconstructed what had happened on the day the asteroid struck.

First, explains Gulick, the impact made a dent 30 kilometers (18 miles) deep in the Earth’s surface. It was like a trampoline stretching down. Then, like that trampoline bouncing back up, the dent instantly rebounded from the force.

As part of that rebound, shattered granite from 10 kilometers below exploded upward at more than 20,000 kilometers (12,430 miles) per hour. Like a splash, it blasted tens of kilometers high, then collapsed back into the crater. That formed a circular mountain range — the peak ring. The final result was a wide, flat crater about one kilometer (0.6 mile) deep, with a peak ring of granite inside it that’s 400 meters (1,300 feet) high.

“The whole thing took seconds,” Gulick says.

And the asteroid itself? “Vaporized,” he says. “The iridium layer found all over the world is the asteroid.”

an animated illustration showing how the Chicxulub crater probably formed after the asteroid impact
This animation shows how the Chicxulub crater likely formed in the seconds after the asteroid hit. The darker green represents the granite beneath the impact site. Notice the “rebound” action.
Lunar and Planetary Institute

No-good, very bad day 

Close to the crater, the air blast would have reached 1,000 kilometers (621 miles) per hour. And that was just the beginning.

Joanna Morgan is a geophysicist at Imperial College London in England who co-led the drilling expedition with Gulick. She studies what happened immediately after the collision. “If you were within 1,500 kilometers [932 miles], the first thing you would see was a fireball,” says Morgan. “You are dead quite soon after that.” And by “quite soon,” she means instantly.

From farther away, the sky would have glowed bright red. Huge earthquakes would have rocked the ground as the impact rattled the entire planet. Wildfires would have ignited in a flash. The asteroid’s mega-splash would have triggered towering tsunamis that radiated across the Gulf of Mexico. Droplets of glassy, melted rock would have rained down. They would have glowed in the darkening sky like thousands of tiny shooting stars.

a photo of a core from the Chixculub crater sliced in half
David Kring and another member of the expedition examine a rock core collected from the Chicxulub crater. 

Inside the drill core, a layer of rock just 80 centimeters (31 inches) thick records those first days and years after the impact. Scientists call this the “transitional” layer because it captures the transition from impact to aftermath. It holds a jumble of melted rock, glassy droplets, silt washed in by tsunamis and charcoal from forest fires. Mixed in are smashed remains of the last Cretaceous inhabitants.

Thousands of kilometers away from Chicxulub, huge waves sloshed back and forth in Earth’s lakes and shallow seas — like a bowl of water when you slam your fist on the table. One of those shallow seas extended north from the Gulf of Mexico. It covered parts of what is now North Dakota.

There, at a site called Tanis, paleontologists made an amazing discovery. A layer of soft rock 1.3 meters (4.3 feet) thick chronicles the very first moments after impact. It’s as clear as a modern crime scene, right down to the actual victims.

Paleontologist Robert DePalma has been excavating this late-Cretaceous layer for six years. DePalma is the curator of the Palm Beach Museum of Natural History in Florida. He’s also a graduate student at the University of Kansas in Lawrence. At Tanis, DePalma unearthed a jumble of marine fish, freshwater species and logs. He even found what appear to be pieces of dinosaurs. The animals look like they were violently torn apart and tossed around.

By studying the site, DePalma and other scientists have determined that Tanis was a riverbank near the shore of the shallow sea. They believe that the remains at Tanis were dumped within minutes of the impact by a powerful wave called a seiche (SAYSH).

Seiches don’t travel long distances as tsunamis do. Instead, they’re more local, like giant but short-lived ripples. The massive earthquake after the impact likely triggered a seiche here. The huge wave would have radiated across the sea, tumbling fish and other animals ashore. More waves buried everything.

a photo of a bunch of tektites, glassy globs and drops of rock
These tektites are droplets of glassy rock that were melted, blasted into the sky and then rained down after the impact. Researchers collected these in Haiti. Similar tektites come from North Dakota at the Tanis site.
David Kring

Mixed into the debris at Tanis are little beads of glass called tektites. These form when rock melts, gets blasted into the atmosphere, then falls like hail from the sky. Some of the fossilized fish even had tektites in their gills. While taking their last breaths, they would have choked on those beads. 

The age of the Tanis deposit and the chemistry of its tektites are an exact match for the Chicxulub impact, DePalma says. If the creatures at Tanis really were killed by the effects of the Chicxulub impact, they are the first of its direct victims ever found. DePalma and 11 co-authors published their findings April 1, 2019, in the Proceedings of the National Academy of Sciences.

Big chill

The asteroid didn’t just vaporize itself. The strike also vaporized sulfur-rich rocks beneath the Gulf of Mexico.

When the asteroid hit, a plume of sulfur, dust, soot and other fine particles shot well over 25 kilometers (15 miles) into the air. The plume quickly spread around the globe. If you could have seen Earth from space then, Gulick says, overnight it would have transformed from a clear blue marble to a hazy brown ball.

On the ground, the effects were devastating. “Just the soot by itself would have basically blocked out the sun,” Morgan explains. “It caused very rapid cooling.” She and her colleagues used computer models to estimate just how much the planet cooled. Temperatures plunged by 20 degrees Celsius (36 degrees Fahrenheit), she says.

For about three years, much of Earth’s land surface stayed below freezing. And the oceans chilled for hundreds of years. Ecosystems that had survived the initial fireball later collapsed and vanished.

Among animals, “Anything bigger than 25 kilograms [55 pounds] would not have survived,” Morgan says. “There was not enough food. It was cold.” Seventy-five percent of Earth’s species went extinct.

a fossilized fish tail seperated from its owner in a seiche
This fossilized fish tail from Tanis, in North Dakota, was ripped off its owner by a violent sloshing wave called a seiche. Earthquakes in the moments immediately after the asteroid impact triggered that seiche.
Robert DePalma

From crater of death to cradle of life

Yet some species were suited to survive the devastation. The tropics stayed above freezing, which helped some species there endure. The oceans also didn’t cool as much as the land had. “Things that survived best were ocean-bottom dwellers,” says Morgan.

Ferns, which are tolerant of darkness, led the recovery of plants on land. In New Zealand, Colombia, North Dakota and elsewhere, scientists have discovered rich pockets of fern spores just above the iridium layer. They call it the “fern spike.”

There also were our small, furry mammal ancestors. These creatures didn’t need much to eat. They could withstand cold better than could large reptiles, such as the dinosaurs. And they could hide for a long time, if needed. “Small mammals could burrow or hibernate,” Morgan points out.

Even within the Chicxulub crater, life came back surprisingly quickly. The intense heat of the impact would have sterilized much of the area. But Christopher Lowery found signs that some life returned within just 10 years. He studies ancient marine life at the University of Texas in Austin.

In rock cores from the 2016 drilling expedition, Lowery and his colleagues found fossils of single-celled creatures called foraminifera (For-AM-uh-NIF-er-uh). These tiny, shelled animals were some of the first life to reappear in the crater. Lowery’s team described them in the May 30, 2018 issue of Nature.

In fact, says Kring, life may have bounced back extra rapidly here. “Surprisingly, recovery within the crater was faster than some other places farther from the crater,” he notes.

a map showing a circle of sinkholes, called cenotes, created around the southern edge of the Chicxulub crater
Viewed from above, a semicircle of sinkholes (blue dots) called cenotes marks the southern edge of the buried Chicxulub crater on the Yucatán Peninsula.
Lunar and Planetary Institute

Lingering heat from the impact may have supported a hotbed of microbes and other new life. As at hydrothermal vents in today’s oceans, hot water flowing through the fractured, mineral-rich rock within the crater could have supported new communities.

The crater, initially a place of violent death, became a cradle for life. The Cretaceous Period was over and the Paleogene Period had begun.

Within 30,000 years, a thriving, diverse ecosystem had taken hold.

Still life with crater

Some scientists debate whether the Chicxulub impact acted alone in wiping out the dinosaurs. Halfway around the planet, in India, a massive outpouring of lava also may have played a role. Yet there is no doubt about the Chicxulub asteroid's devastating impacts, nor the gaping crater it gouged into Earth’s surface.

Over millions of years, the crater disappeared beneath new layers of rock. Today, the only above-ground sign is a semicircle of sinkholes that curves across the Yucatán peninsula like a gigantic thumbprint.

Those sinkholes, called cenotes (Seh-NO-tayss), trace the rim of the ancient Chicxulub crater hundreds of meters below. The buried crater rim shaped the flow of underground water. That flow eroded the limestone above, making it crack and collapse. The sinkholes are now popular swimming and diving spots. Few people who splash in them might guess that they owe their cool, blue waters to the fiery end of the Cretaceous Period.

The vast Chicxulub crater has all but disappeared from view. But the impact of that single day continues 66 million years later. It changed the course of life on Earth forever, creating a new world where we and other mammals now flourish.

a photo of a Mexican cenote, a cavern and a sinkhole with a pool of water at the bottom
Along the buried rim of the Chicxulub crater, water-filled sinkholes similar to these — called cenotes — formed where the rock eroded.
LRCImagery/iStock/Getty Images Plus

Power Words

(more about Power Words)

Alamosaurus     A genus of enormous, long-necked sauropod dinosaurs that lived in the late Cretaceous. The name comes from the sandstone deposits in New Mexico where their fossils were first found. The size of their vertebrae suggest these could have been one of the biggest dinosaurs in North America.

asteroid     A rocky object in orbit around the sun. Most asteroids orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.

atmosphere     The envelope of gases surrounding Earth or another planet.

Caribbean     The name of a sea that runs from the Atlantic Ocean in the East to Mexico and Central American nations in the West, and from the southern coasts of Cuba, the Dominican Republic and Puerto Rico down to the northern coasts of Venezuela and Brazil. The term is also used to refer to the culture of nations that border on or are islands in the sea.

cenotes     (in geology) The name for sinkholes in limestone rock found throughout Mexico’s Yucatán Peninsula.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemistry     The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) Chemistry also is used as a term to refer to the recipe of a compound, the way it’s produced or some of its properties. People who work in this field are known as chemists.

Chicxulub     The name given an asteroid (or possibly a comet) that crashed into Earth around 66 million years ago. It left a crater more than 180 kilometers (110 miles) wide near the town of Chicxulub in what is now Mexico. The collision released an immense amount of energy — equivalent to billions of atom bombs the size of those dropped on Japan during World War II. This event changed the planet’s climate and is widely believed to have triggered a mass extinction of species — including the end of the dinosaurs.

colleague     Someone who works with another; a co-worker or team member.

computer model     A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

core     Something — usually round-shaped — in the center of an object. (in geology) Earth’s innermost layer. Or, a long, tube-like sample drilled down into ice, soil or rock. Cores allow scientists to examine layers of sediment, dissolved chemicals, rock and fossils to see how the environment at one location changed through hundreds to thousands of years or more.

crater     A large, bowl-shaped cavity in the ground or on the surface of a planet or the moon. They are typically caused by an explosion or the impact of a meteorite or other celestial body. Such an impact is sometimes referred to as a cratering event.

Cretaceous     A geologic time period that included the end of the Age of Dinosaurs. It ran from roughly 145.5 million years ago until 65.5 million years ago.

curator     Someone who manages a collection of items, for instance in a museum, library or art gallery. This person’s primary job is to design exhibits, organize and acquire collections and do research on the artifacts included in the collection.

debris     Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft.

dinosaur     A term that means terrible lizard. These ancient reptiles lived from about 250 million years ago to roughly 65 million years ago. All descended from egg-laying reptiles known as archosaurs.

ecosystem     A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra. The term can also be applied to elements that make up some an artificial environment, such as a company, classroom or the internet.

element     A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

expedition     A journey (usually relatively long or over a great distance) that a group of people take for some defined purpose, such as to map a region’s plant life or to study the local microclimate.

extinct     An adjective that describes a species for which there are no living members.

extinction     The permanent loss of a species, family or larger group of organisms.

fireball     A lump of rock or metal from space that hits the atmosphere of Earth. Fireballs are meteors that are exceptionally bright and large.

foraminifera     Single-celled organisms (neither plants nor animals) that are abundant in ocean water. They make up the base of the marine food web.

force     Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.

fossil     Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.

freshwater     A noun or adjective that describes bodies of water with very low concentrations of salt. It’s the type of water used for drinking and making up most inland lakes, ponds, rivers and streams, as well as groundwater.

geologic     An adjective that refers to things that are related to Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists.

geologic record     Mineral deposits and fossils that form in rock. Geologists can “read” these minerals to decipher what Earth’s climate and geology was like (such as dry spells, earthquakes or volcanic eruptions) when the rocks’ ingredients were laid down. Fossils and other minerals can signal what life may have existed during that same period.

gills     The respiratory organ of most aquatic animals that filters oxygen out of water. Fish and other water-dwelling animals use gills to breathe.

glass     A hard, brittle substance made from silica, a mineral found in sand. Glass usually is transparent and fairly inert (chemically nonreactive). Aquatic organisms called diatoms build their shells of it.

graduate student     Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).

granite     A type of hard igneous rock, which contains coarse-grained inclusions (essentially mini rocks within a rock) of various minerals, chiefly quartz, feldspar and mica.

hydrothermal vent     An opening at the bottom of the ocean or a lake where hot water emerges from deep inside Earth. The water is rich in minerals and chemicals that can nourish ecosystems of worms, clams, microbes and other organisms.

iridium     Discovered in 1803, its name comes from the Latin for rainbow. It’s a hard, brittle and corrosion-resistant metal in the platinum family. Slightly yellowish, the principle use for this element is as a hardener for platinum. Indeed, its melting point is more than 2,400° Celsius (4,350° Fahrenheit). The element’s atomic number is 77.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

lava     Molten rock that comes up from the mantle, through Earth’s crust, and out of a volcano.

lead      A toxic heavy metal (abbreviated as Pb) that in the body moves to where calcium wants to go (such as bones and teeth). The metal is particularly toxic to the brain. In a child’s developing brain, it can permanently impair IQ, even at relatively low levels.

limestone     A natural rock formed by the accumulation of calcium carbonate over time, then compressed under great pressure. Most of the starting calcium carbonate came from the shells of sea animals after they died. However, that chemical also can settle out of water, especially after carbon dioxide is removed (by plants, for instance).

lunar     Of or relating to Earth’s moon.

mammal     A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.

marine     Having to do with the ocean world or environment.

marsh     A low-lying wetland usually covered with grasses and shrubs, not trees. It’s a prime feeding and nesting ground for waterfowl.

microbe     Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

microscope     An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.

mineral     Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns).

model     A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.

New Zealand     An island nation in the southwest Pacific Ocean, roughly 1,500 kilometers (some 900 miles) east of Australia. Its “mainland” — consisting of a North and South Island — is quite volcanically active. In addition, the country includes many far smaller offshore islands.

Paleogene     That part of the Tertiary Period that ran from 66 million to 23 million years ago.

paleontologist     A scientist who specializes in studying fossils, the remains of ancient organisms.

palm     A type of evergreen tree that sprouts a crown of large fan-shaped leaves. Most

peak ring      An uplifted, circular ring of rock within an impact crater

peninsula     A parcel of land that is that is attached to the mainland but surrounded by water on three sides.

physical     (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

plume      (in geology) Fluids (air, water or magma typically) that move, largely intact, in a feather-like shape over long distances.

pressure     Force applied uniformly over a surface, measured as force per unit of area.

Proceedings of the National Academy of Sciences     A prestigious journal publishing original scientific research, begun in 1914. The journal's content spans the biological, physical, and social sciences. Each of the more than 3,000 papers it publishes each year, now, are not only peer reviewed but also approved by a member of the U.S. National Academy of Sciences.

range     The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (in math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

seiche     A temporary disturbance or oscillation in the water level of a lake or other enclosed body of water, especially one caused by changes in atmospheric pressure.

silt     Very fine mineral particles or grains present in soil. They can be made of sand or other materials. When materials of this size make up most of the particles in soil, the composite is referred to as clay. Silt is formed by the erosion of rocks, and then usually deposited elsewhere by wind, water or glaciers.

sinkhole     A body of water that forms when a patch of ground opens up, revealing a rocky cavern below. That rocky structure then accumulates rainwater because there no opening below that allows the water to easily exit. Some sinkholes develop naturally. Others can result from the overpumping of any groundwater that may have collected in the rocky underground cavern. Sinkholes can be as small as a meter across or as large as a big lake.

soot     Also known as black carbon, it's the sometimes oily residues of incompletely burned materials, from plastics, leaves and wood to coal, oil and other fossil fuels. Soot particles can be quite small — nanometers in diameter. If inhaled, they can end up deep within the lung.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

spore     A tiny, typically single-celled body that is formed by certain bacteria in response to bad conditions. Or it can be the single-celled reproductive stage of a fungus (functioning much like a seed) that is released and spread by wind or water. Most are protected against drying out or heat and can remain viable for long periods, until conditions are right for their growth.

sulfur     A chemical element with an atomic number of sixteen. Sulfur, one of the most common elements in the universe, is an essential element for life. Because sulfur and its compounds can store a lot of energy, it is present in fertilizers and many industrial chemicals.

tektite     A small glassy object formed by the cooling of melted rock. These may develop when an asteroid strikes Earth, melting rocks and blasting that melted material high into the air. The solidifying glassy materials can be as large as several centimeters in diameter.

transition     The boundary where one thing (paragraphs, ecosystems, life stage, state of matter) changes or converts into another. Some transitions are sharp or abrupt. Others slowly or gradually morph from one condition or environment to another. 

tropics     The region near Earth’s equator. Temperatures here are generally warm to hot, year-round.

tsunami     One or many long, high sea waves caused by an earthquake, submarine landslide or other disturbance.

vaporize     To convert from a liquid to a gas (or vapor) through the application of heat.

volcano     A place on Earth’s crust that opens, allowing magma and gases to spew out from underground reservoirs of molten material. The magma rises through a system of pipes or channels, sometimes spending time in chambers where it bubbles with gas and undergoes chemical transformations. This plumbing system can become more complex over time. This can result in a change, over time, to the chemical composition of the lava as well. The surface around a volcano’s opening can grow into a mound or cone shape as successive eruptions send more lava onto the surface, where it cools into hard rock.

wave     A disturbance or variation that travels through space and matter in a regular, oscillating fashion.


Journal: R. A. DePalma et al. A seismically induced onshore surge deposit at the KPg boundary, North Dakota. Proceedings of the National Academy of Science. Vol. 116, April 23, 2019, p. 8190. doi: 10.1073/pnas.1817407116.

Journal: C.M. Lowery et al. Rapid recovery of life at ground zero of the end-Cretaceous mass extinction. Nature. Vol. 558, June 14, 2018, p. 288. doi: 10.1038/s41586-018-0163-6

Meeting: D.A. Kring et al. Probing a post-impact hydrothermal system in the Chicxulub crater with core recovered by the IODP-ICDP Expedition 364. Geological Society of America Annual Meeting. October 24, 2017. Seattle, Washington.

Meeting: C. Lowery et al. The recovery of life at ground zero. Geological Society of America Annual Meeting. October 24, 2017. Seattle, Washington.

Meeting: J. Morgan et al. The release of climatic gasses by the Chicxulub impact. Geological Society of America Annual Meeting. October 24, 2017. Seattle, Washington.

Meeting: S. Gulick et al. First day of the Cenozoic: processes recorded within the Chicxulub Crater at IODP-ICDP site M0077. Geological Society of America Annual Meeting. October 24, 2017. Seattle, Washington.

Other abstracts also at: Geological Society of America Annual Meeting, Seattle, October 2017: Session P3: IODP-ICDP Expedition 364 to Chicxulub Crater.