[♪ INTRO]
Another year of the pandemic has come and gone.
A lot of science news this year has been focused on the vaccines,
new variants, and the rest of our ongoing collective misfortune.
But science has carried on -- and there have been plenty of amazing discoveries
this year that had nothing to do with COVID.
We think they deserve the spotlight too, so here are three science stories
you might have missed this year.
Since the 1980s, scientists have been pretty sure that dinosaurs died out
during a mass extinction event caused by a roughly 10 kilometer meteorite
hitting the Earth’s surface around 66 million years ago.
We’ve even found the likely scene of the crime: a crater about 180 to 200 kilometers
in diameter on the Yucatan peninsula of Mexico, called Chicxulub.
But where that meteorite came from has continued to be a puzzle.
It came from space, but we’re trying to be more specific than that.
We know from studying the crater that the object was likely made up of carbon,
along with other elements.
Previous research had pointed to the breakup of the Baptistina asteroid family.
So, it would be one of 2500 smaller asteroids that formed
after a large asteroid broke up 160 million years ago.
But the Baptistina asteroids were made of iron and magnesium silicates.
Also, the timing of the Baptistina breakup didn’t quite fit.
The other option was that it was just a normal background asteroid
that just happened to hit the Earth.
But mathematically, an asteroid from the main asteroid belt made out of carbon
is only going to hit Earth once every 3.5 billion years,
which would be basically once in the entire history of life.
Now, comets are more likely to be carboniferous.
But a comet the right size hitting Earth is even less frequent,
like, once every 4 to 11 billion years.
So, it’s been a pretty weird mystery.
But this year, astronomers at Harvard did the math and realized that a
carboniferous comet from the edge of the solar system could have been knocked off
course by Jupiter, changing its orbit and sending it toward the sun.
When it got close to the sun, gravitational forces could have broken it apart,
sending pieces flying into Earth’s orbital path.
And the more objects crossing into Earth’s orbit,
the more likely one is to actually hit the Earth.
Sure enough, their model predicts carboniferous objects threatening Earth
at just about the right time and frequency to have made the Chicxulub crater.
This is also consistent with other carboniferous impact craters
in South Africa and Kazakhstan.
So these astronomers might have actually figured out
where the comet that killed the dinosaurs came from.
And 2021 wasn’t just a big year for ancient critters.
It was also a big year for ancient art.
Several discoveries this year brought us some of the earliest known
examples of hominin art.
In Israel, archaeologists discovered a wild ox bone
with six nearly parallel incisions dating back 120,000 years.
Now, I know that a bone with straight lines carved into it may not seem like art,
but anthropologically, it’s a reflection of what’s called symbolic mediated behavior.
These are practices where something takes on a meaning more than just
functional use that depends on collectively shared beliefs.
Funeral practices, decorative jewelry or clothing, cave painting,
and engraving are all considered symbolic behaviors.
These practices are important in human history, because they reflect the development
of organized thinking and communication between members of a group.
Now, the researchers can’t say for sure what the incisions mean,
because they don’t match any previously discovered patterns.
But whatever it represented, this bone is the oldest known example of symbolic
representation from the Middle East, suggesting that collective symbolic
meaning developed in the region earlier than scientists had thought.
And in the Tibetan Plateau, archaeologists discovered the oldest
known art made on an immobile rock surface.
They found impressions of hand- and footprints made in soft limestone
that dated back to between 169,000 and 226,000 years.
They were able to rule out that the handprints ended up there through everyday
movement or from someone using their hands to stabilize themselves.
The impressions were made intentionally.
And what’s more, they were made by children.
That’s right, these are basically the two hundred thousand year old version of the
concrete stepping stone with your handprint in it that is still in your parents’ backyard.
If that’s not adorable, I don’t know what is.
Before this discovery, the oldest handprint art was paintings that used hands as
stencils dating back 40,000 years, and these impressions are way older than that.
And maybe more importantly, it may reflect that the earliest artists were actually kids,
or at least that kids of the time may have used art
and creative expression when they played.
Ancient hominins. They’re just like us!
And we didn’t just learn about modern human development this year.
We also learned more broadly about mammal development.
Traditionally, somewhere between 20% and 92% of our DNA
has been thought of as non-functional.
It’s often been maligned as “junk DNA”.
And the junkiest of our DNA are transposons,
also called transposable elements, or TEs.
These segments of DNA make up around 50% of the human genome.
They jump around to different places on the genome, and as far as we’ve known for a
long time, they don’t do much else except sometimes cause problems when they land.
A few transposable elements have taken on new, more helpful functions over time,
helping to determine how and when other parts of the genome get used.
But it’s not totally clear if that regulation is helpful,
or hurtful, or even makes any difference at all.
So this year, scientists took a closer look at a specific TE.
It’s known to regulate the expression of a gene called Cdk2ap1.
That gene is involved in embryonic cell replication,
and when and how embryos implants in the uterus.
They bred some mice that had the gene, but were missing the TE regulating it.
And half of the resulting mouse pups died at birth.
Normally, Cdk2ap1 becomes more active around 24 hours before embryo implantation.
When that gene isn’t working, embryos can’t implant correctly,
causing serious complications for the parent and offspring.
Now, other mammals don’t have this same TE, but the researchers did find analogous
sections of DNA in seven other mammal species, including humans.
And all of them seem to switch on before embryo implantation.
This is the first time that scientists have reported a TE
being critical to mammalian development.
But if mice can’t survive without it, that suggests they need the TE
to help switch on Cdk2ap1, which in turn is required for implantation.
And that is pretty compelling!
Plus, it has implications for human fertility.
A huge number of miscarriages in humans don’t have a clear genetic reason.
It’s possible that the answer may actually lie in a transposon,
just like with the knockout mice.
So it turns out that DNA that was once trash, might actually be treasure.
Thanks for watching this episode of SciShow, which was brought to you today
and for all of 2021 by the generous support of our patrons.
If you’d like to get involved next year, you can get started at patreon.com/scishow.
We have some great perks for you there, and also, we will be eternally grateful.
[♪ OUTRO]