Stated clearly presents
The scientific saga of Dr. Mary Schweitzer
and her discovery of soft tissue inside a dinosaur bone!
In 2003 a team of paleontologists finished excavating an incomplete, yet extremely well-preserved T. rex skeleton.
During transport the animal's femur, its thigh bone, had to be broken in two.
While the bone was eventually put back together, pieces that had fallen out were kept separate and then sent to
Doctor Mary Schweitzer for dissection and analysis.
After applying a mild acid to the fragments to remove hard minerals,
a diverse collection of soft material could be seen under the microscope.
It included what looked like cells and tiny blood vessels.
They were very degraded but similar to those commonly found inside fresh bone.
Chemical analysis further revealed what looked like animal proteins.
Dr. Schweitzer was shocked.
According to our understanding at the time,
unless treated with chemicals, the way that leather is, for example,
and then further sealed for preservation, soft tissue was predicted to completely deteriorate,
even under the best of circumstances,in less than 1 million years.
This t-rex leg bone, however, was thought to be millions of years old.
What did this discovery of soft tissue mean?
To Dr. Schweitzer, and to many other researchers, there were three main possibilities.
Number 1: The fossil might be far younger than previously thought, maybe even less than 1 million years old.
Number 2: The fossil could have been recently contaminated by microbes that produced the soft structures after the bone had fossilized,
a substance known as biofilm.
Option number 3: There might be a previously unknown
natural mechanism capable of preserving soft tissue far longer than 1 million years.
Having studied paleontology throughout her career,
Dr. Schweitzer immediately knew that option number 1 was least likely.
The fossil had been found in a set of rock layers known as the Cretaceous,
ancient sediments laid down between 145 to 66 million years ago.
Our understanding of the age of these rocks is founded on thousands of data points
telling us how rock layers form on the careful study of the rise and fall of various ecosystems
in the animal groups in the fossil record and on the clear results of hundreds of experiments on radiometric dating.
Many overlapping radiometric dating methods have been used to confirm the age range of Cretaceous rocks
and the results have been independently checked by laboratories around the globe.
To successfully argue that her single discovery means that the fossil is actually young
she would have to ignore everyone else's careful observations.
Given the extreme imbalance of evidence, it seemed to her, and to other well-informed thinkers,
that option number one was not plausible.
Early on, her colleagues argued that option number two was most likely.
As is the custom in science, papers were published critiquing Dr. Schweitzer's work.
Many of them suggested that what she had found was actually biofilm.
After closer examination, several years of debate
and many papers published back and forth, however,
the scientific community is now largely convinced:
The soft tissue that Dr. Schweitzer found IS authentic. It did come from the original T. rex.
This left informed thinkers to suspect that option number three was most likely, but how?
What natural process or collection of natural processes
could allow soft tissue to remain intact for over 66 million years?
Nobody had an answer but Dr. Schweitzer was determined to figure it out.
As luck would have it, when first uncovering her discovery, she randomly attended a lecture
on brain disease which focused on the destructive power of free iron particles on living tissue.
Iron is extremely common in our blood.
Normally, however, it's trapped safely inside hemoglobin
a blood protein that uses iron to capture oxygen in the lungs and deliver it throughout the body.
While iron is safe and highly useful inside hemoglobin, loose iron particles can wreak havoc on our cells.
In a process called cross-linking,
iron can trigger a series of chemical reactions, eventually causing proteins and other cellular structures
to unravel and fuse together in a tangled useless mess.
In living animals, cross-linking is bad.
In dead tissue, however, Dr. Schweitzer knew that cross-linking leads to preservation.
Chemicals that we use to turn delicate animal skins into tough durable leather
do so by cross-linking proteins.
Formaldehyde, the chemical used to preserve soft tissue in museum specimens,
also uses cross-linking to do its work.
When Dr. Schweitzer examined the soft tissue from her dinosaur fossil
she found that it was saturated in iron crystals.
When the T. rex had died, blood must have begun to decompose, releasing iron from hemoglobin.
As iron spread through tissue and bone it initiated cross-linking.
The soft tissues most affected would have been preserved like leather for a long period of time.
Tissues that were both cross-linked and sealed safely inside hard bone were double protected,
allowing them to survive for millions of years until present day.
Based on the evidence, her explanation seemed reasonable, but, being a trained scientist,
Dr. Schweitzer was not satisfied until she found a way to test her idea.
To do so, she designed an experiment.
Ostriches are among the closest living relatives to dinosaurs.
Their bones are rich in blood vessels, just like those found in the fossil.
She obtained an ostrich femur and extracted the vessels using a series of acid and enzyme treatments.
At room temperature, one group of blood vessels was placed in a watery iron-free solution.
She wanted to find out how long the vessels took to decompose.
A second batch was placed in a solution of iron rich hemoglobin.
The vessels in normal solution turned to mush in just three days,
quickly destroyed by microbes and other natural chemical reactions.
After two years, vessels soaked in iron rich hemoglobin remained completely intact.
No signs of degradation could be found.
Now, of course, two years is a far cry from 66 million years.
Further experiments may reveal that there is more to this mystery, but Mary Schweitzer's discovery
has opened us up to a new understanding of how decomposition works in large animals.
Furthermore, her story is a beautiful example of how good science is done.
She began by making an observation;
presented that observation to the scientific community, for their feedback and critique;
she then came up with an explanation, or hypothesis, for the observation;
and finally, using her creativity, she designed an experiment to test that hypothesis.
Now that we know soft tissue can be preserved naturally, far longer than previously imagined,
researchers have began looking for, and finding, soft tissue in the fossils of many different species.
The study of these ancient structures
is helping increase our understanding of how extinct animals
once lived and evolved on our planet.
I'm John Perry and that is the scientific saga of Dr. Mary Schweitzer, stated clearly.
Special thanks to Dr. Mary Schweitzer.
She spent a lot of time with me on the phone and back and forth in email with me as I was studying for and
writing this script. Thank you Mary for all of your assistance
Dr. Schweitzer's work is continuing.
You can follow what she's up to at molecularpaleo.wordpress.ncsu.edu
This animation was funded by viewers like you, who contribute to us on patreon.com/statedclearly. I really appreciate all the support
you've given me. I really could not continue doing them without you.
Last but not least, we have dinosaur t-shirts available. You can find a link to order yours down in the video description.
So long for now. Stay curious.