Dinosaurs dying at the end of the Cretaceous Period. Volcanism is thought to be one of the main causes of the dinosaurs dying out.
Click on image for full size
Courtesy of NSF

K-T Extinction (Why Did the Dinosaurs Go Extinct?)

Why did the dinosaurs go extinct? No one knows for sure, and scientists have come up with a number of theories to explain why the dinosaurs suddenly died out about 65 million years ago.

The most prominent theories about the cause(s) of the dinosaurs’ demise are based on the fact that scientific evidence shows us that at the time the dinosaurs died out, the Earth experienced increased volcanism as well as a number of major collisions with asteroids or comets. This extinction event is referred to as the the Cretaceous-Tertiary Mass Extinction or the K-T Extinction (because it marks the boundary between the Cretaceous Period, which is often abbreviated with the letter K, and the Tertiary Period), and it wasn't just the dinosaurs that went extinct--roughly two thirds of all of the plant and animal species on Earth disappeared.

Most scientists believe that increased volcanic activity may have introduced dust particles into the atmosphere, causing a drop in photosynthesis (and plant growth). This would have weakened the Earth’s ability to support the ecosystems that thrived in the Cretaceous Period, and scientists believe that the problem was made much worse when one or more large asteroids impacted the Earth, throwing a massive cloud of dust and toxic chemicals like sulfuric acid into the atmosphere. It is commonly thought that this event poisoned the Earth’s atmosphere for years, making plant and plankton growth impossible and fatally disrupting food chains worldwide.

There are other factors that may have contributed to the dinosaurs’ extinction. For instance, during the Cretaceous Period, we know that the oxygen levels in the Earth’s atmosphere were much higher than today. This means that when a large asteroid impacted the Earth, there could have been large firestorms, which would have caused a temporarily increased greenhouse effect that could have killed off a large number of organisms. There is also evidence to suggest that the Earth’s sea levels dropped significantly during the K-T boundary, and although no one knows exactly what caused this, we can see that this could have caused widespread climate changes and contributed to the dinosaurs’ extinction as well.

There are other theories that are less widely accepted; for instance, some scientists believe that the dinosaurs went extinct because mammals became very good at eating the dinosaurs’ eggs. Others believe that there was a supernova explosion near Earth, and the radiation from this explosion poisoned the majority of life on Earth. No one knows for sure the reason the dinosaurs died out - it is a source of scientific debate. There are many scientists around the world still conducting research in order to test different theories and answer this question.

Last modified March 25, 2010 by Jennifer Bergman.

You might also be interested in:


Photosynthesis is the name of the process by which autotrophs (self-feeders) convert water, carbon dioxide, and solar energy into sugars and oxygen. It is a complex chemical process by which plants and...more

Biomes and Ecosystems

Biomes are large regions of the world with similar plants, animals, and other living things that are adapted to the climate and other conditions. Explore the links below to learn more about some of the...more

Earth's Greenhouse Effect

Energy from the Sun can enter the atmosphere, but not all of it can easily find its way out again. This is a natural process called the greenhouse effect. Without any greenhouse effect, Earth’s temperature...more

The Scientific Process

How does scientific research actually work? How do scientists actually come up with explanations for the things that happen around us? The first step in the scientific process occurs whenever a scientist...more

New Blow for Dinosaur-Killing Asteroid Theory

The enduringly popular theory that the Chicxulub crater holds the clue to the demise of the dinosaurs, along with some 65 percent of all species 65 million years ago, is challenged in a paper to be published...more

Revisiting Chicxulub

For decades, scientists have accumulated ever-larger datasets that suggest an enormous space rock crashed into the ocean off the Yucatan Peninsula more than 65 million years ago, resulting in the Cretaceous-Paleogene...more

The Archean

The Archean is the name of the age which began with the forming Earth. The duration of the Archean, 2.8 billion years, is more than half the expected age of the Earth. We don't know much about this period,...more

Salts included in the Earth's early ocean

We all know that salt is a big part of the ocean water today. Two things help scientists figure out what chemicals may have been part of the Earth's early oceans. Igneous rocks are made of iron, aluminum,...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA