How Do We Know Dinosaurs Existed Millions of Years Ago?

Dinosaurs are one of the most famous groups of animals to have ever lived. They are universally known and featured in countless books, films, and television shows. One of the most common questions is, “How do we know dinosaurs existed millions of years ago?” and “How long ago did they live?” 

There’re many different ways that scientists can estimate the age of rocks and fossils. These methods range from relative dating (i.e., determining if one rock layer is older or younger than another) to absolute dating (i.e., pinpointing when something occurred).


Unsplash

Fossils, the Remains of Prehistoric Life

Fossils are the remains of prehistoric life. They can be found in sedimentary rock layers. Fossils are the best evidence of prehistoric life from millions of years ago, making them very important when studying the history of Earth and its creatures. 

Fossils can also date a sedimentary rock layer because they’re deposited at a specific period and cannot move around on their own once buried in rocks below ground level. This evidence helps us determine how old certain fossils are—and by extension, how long ago they lived.

Dating Methods

Dating fossils is one of the essential tools paleontologists have to determine the age of dinosaurs and their prehistoric neighbors. Learn the basics.

1. Relative dating 

Scientists based this technique on the principle that you can determine an object’s age by comparing it to similar objects found in the same place. What makes something old can be different kinds of evidence, but no matter what kind, it tells us one thing: the longer something happened, the harder it is to find evidence that proves it. 

Relative dating is a method used by paleontologists and other scientists to figure out whether something happened before or after something else; it doesn’t tell us exactly how old something is. It works by looking at the differences between a recent event and an older one.

One great example of this is cave painting. Cave paintings have been dated thousands of years old and are found in the same caves as mud paintings. It’s clear that cave paintings are much older than mud paintings because they came first. Mud paintings are like modern-day finger painting, but cave paintings involve more skill, practice, and a good eye for designs and patterns. 

2. Absolute dating 

This absolute dating method assumes that every material contains certain isotopes (atoms with different numbers of neutrons) that decay over time at a known rate (called half-lives). For example, if we knew how long ago an organism died and had a sample of its remains within ten years of its death, we could determine its age by measuring how much carbon-14 was left in its body compared with the amount present today.

3. Radiometric dating 

Radiometric dating generally involves measuring traces of radioactive materials incorporated into rocks when they were formed. By calculating these rates against known models for uranium accumulation over time (known as radiometric dating), geologists can estimate when two rocks separated from each other—even if these occurred millions or even billions of years ago.

4. Stratigraphic dating 

Paleontologists based this method on the principle that different rock layers were formed at different times. Dinosaur bones have been unearthed worldwide, and the evidence from these fossils can tell us a lot about how old they are. This information comes from a branch of science called stratigraphy. 

Stratigraphy is the study of rock layers or strata. When you go out into the field to look for fossils, you observe stratigraphic layers and how they’re laid down in sequence. The basic idea is simple: the lower layers are older than the upper layers. 

This sequence works because different types of sediment get deposited at different rates depending on what kinds of environments exist at the time. For example, if a river floods and dumps a load of sediment into an area, it’ll slowly settle in layers over time. 

Like a lake, a slower-moving body of water will create layers too. Still, those will form more gradually over an extended period because less energy is involved in their formation. The fossils within these rock layers help us date them by providing markers for relative age. 

For example, if fossils are found in a layer of sedimentary rock, and they’re similar to those found in another layer above it, then we know that the two layers must have been deposited around the same time.

5. Biological dating

During the Jurassic period (200 million years ago), dinosaurs roamed the Earth. Birds are descended from those dinosaurs—their ancestors are the fossilized bones that paleontologists search for today. But how do paleontologists know that?

Using fossils as a dating tool is called “biological dating,” and it’s based on the fact that different species of plants and animals appeared at different times in Earth’s history. By comparing the age of fossils found in a particular stratum with those of other layers, geologists can determine when they were formed.

When a layer is exposed at the surface, it undergoes chemical alteration by water and air. That chemical change is then reflected in any previously deposited layers beneath it, which you may preserve for future generations to find and interpret. The chemical changes become increasingly pronounced over time, making it possible for scientists to accurately date sedimentary rock layers thousands of years old or more.

6. Potassium-argon dating 

Tiny dinosaur bones are fun to find, and it’s neat to imagine prehistoric creatures running around on the same Earth we walk on today. It’s a little harder to believe that those bones were once part of a living creature from so long ago. The idea that things could be millions of years old can seem impossible. Yet there’re ways to figure out the age of ancient things, and that’s where potassium-argon dating comes in.

How does it work? This isotopic system measures the amount of potassium-40 in a sample, a radioactive isotope with a half-life of 1.25 billion years. When an atom of this element decays, it becomes argon-40, which has a half-life of 50 billion years—so even though it’s not radioactive itself, it gives scientists an idea about how old the sample is based on when the potassium-40 decayed into argon-40.

Every rock has some amount of potassium-40 in it, depending on its type: granite contains about 0.01% potassium-40, while basalt has 3%-14%. The closer this ratio is to 40, the further away from the Earth’s surface the rock sample is derived. Scientists use the technique to estimate the ages of rocks that they study.

7. Dendrochronology 

While dinosaur bones provide plenty of clues about the prehistoric giants, there was a time before they were even discovered when scientists were having trouble proving their existence. But thanks to a method known as dendrochronology, we can now determine how long ago certain species of dinosaurs lived by examining the rings of trees that existed simultaneously. 

As each tree grows, its trunk creates a pattern of growth rings that are affected by weather conditions like the amount of rainfall or temperature. By looking at patterns in these tree rings, scientists can see similarities between ring patterns from ancient trees and those surrounding them today. 

This method stems from the principle that trees have annual growth rings. Geologists can determine when a tree died by counting back from the outermost ring to find the year when it was formed.

They then compare those similarities to similar growth patterns in fossilized dinosaur skeletons, which provides evidence for the ages at which dinosaurs existed. Since fossilized bones can indicate what species a dinosaur is, it also gives us clues about related species and how they live.

We can now use dendrochronology to look at ancient dinosaurs and other animals that lived alongside them, such as giant tortoises and saber-toothed tigers. It’s even been used to help us understand the lives of our early ancestors—we know now that Neanderthals had been around for more than 100,000 years before modern humans developed languages. 

8. Radiocarbon dating 

Radiocarbon dating is a technique scientists use to learn when organisms (plants, animals, or even humans) die. It uses the naturally-occurring radioisotope carbon-14 (also known as radiocarbon), which forms in the upper atmosphere. Because it’s unstable, carbon-14 decays at a constant rate into nitrogen-14. 

Scientists use the ratio of carbon-14 to carbon-12 and carbon-13 in a sample and its surroundings to figure out how long ago the organism died. Scientists can use this technique to determine how long ago fossilized organisms were alive since a fossil is an imprint or trace of an organism that died in the past. 

Fossilization usually occurs when an organism is buried quickly by sediment or volcanic ash before it has a chance to decay away. Moreover, fossils are typically formed under conditions without oxygen (anoxic), so there’s no risk of carbon-14 escaping through decay by bacteria. Once the organism is trapped in rock, it will remain there for millions of years.

Conclusion

Dinosaur fossils are the remains of living things that have been preserved for thousands and millions of years. Scientists use various methods to date these fossils, including relative, absolute, and radiometric dating methods. These methods rely on sedimentary rock layers’ geometric patterns and continuity.