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We’re covering the gamut of scale on SciShow
News this week,
from fundamental particles to the time when
life started getting bored of being microscopic
and grew much bigger.
We’ll start with the particles, because
physicists just found a new one.
Most of the familiar, mass-having stuff around
us is made of quarks.
Three quarks join up to form a baryon, like
a proton or a neutron.
A proton is made of two up quarks and one down quark,
and a neutron is two down quarks and an up quark.
But there are six varieties of quarks: up,
down, strange, charm, top, and bottom.
And according to the Standard Model, the physics theory that describes how the subatomic universe works,
any of those six are fair game to make a baryon.
On July 6th, CERN scientists announced they
had found a new particle with the catchy name
Xicc++,
made of two charm quarks and one up quark.
And this gives us a new tool to study one
of the fundamental forces that binds our universe together.
The names of quarks don’t really have anything
to do with their properties.
But the important thing here is that the up and
down quarks are much lighter than the other four,
like charm and strange.
We’ve observed some heavier baryons before.
Lambda particles, for instance, can have one charm or one strange quark alongside an up and a down.
But the new CERN particle has two charms,
making it nearly four times heavier than a proton!
The data was gathered last year by the Large
Hadron Collider beauty experiment.
This detector is extra good at measuring particles
that form after smashing protons together,
and their radioactive decay products.
And this is the first time scientists have
confidently observed a baryon containing
two heavier flavors of quark.
Now, this finding doesn’t really shake up
our understanding of particle physics.
The Standard Model predicts the existence
of these baryons, so they weren’t, like,
a huge surprise.
But being able to observe them is really important,
because it gives physicists a new tool
to examine the strong force, the fundamental
force that holds quarks together.
Inside a baryon like a proton, the three light
quarks are pretty evenly balanced and zip
around each other.
If they stray a little too far, the strong
force pulls them back, refusing to let them split up.
When two of the quarks are heavy, physicists
expect that the lighter quark will circle
around them,
kind of like a planet around a binary star
system.
CERN scientists hope that studying these double-charm
particles, learning more about their lifetime
and how often they form, will let them see
if these expectations are true.
And with more data, researchers can keep updating
our theories about the strong force.
As always, there’s still more work to do.
For example, scientists at Fermilab thought
they found a double-charm baryon way back
in 2002.
That finding isn’t as statistically strong
as this new one, though, because the mass
was too light
and it decayed faster than physicists had
expected.
But even though the data doesn’t square
up with this new, more confident finding,
it hasn’t been ruled out completely.
So some researchers are working on a way to
explain both observations.
Going from the very small to the surprisingly
big: Life has been microscopic for most of
history, so why did it get big in the last
few hundred million years?
It may sound like something out of an RPG, but a rangeomorph is a very old form of multicellular life,
dating about 571 million years ago to the
mid-Ediacaran period.
Rangeomorphs were probably animals, but they’re
so primitive and vaguely fern-like that it’s
hard to be sure.
They have no mouths, no guts, no side-to-side
symmetry, and certainly no squishy fish cheeks.
They aren’t the earliest animals, if they’re
animals at all, but they’re some of the
first big ones.
Some of them stayed under ten centimeters
tall, but others could get up to two meters.
And a study out this week in Nature Ecology
and Evolution suggests a reason why:
they may have been among the first organisms
to change their size and shape because of
changing ocean chemistry.
These researchers studied the shapes of rangeomorph
fossils and developed computer models to simulate
their growth with different amounts of nutrients.
And the simulations suggested that where nutrients
were hanging around probably affected rangeomorph
size and shape a lot.
Scientists call this ecophenotypic plasticity.
It’s why trees grow differently in a dense
forest or an open field,
or why one mollusk might have a different
shell shape depending on where it grows up.
This makes a lot of sense, because rangeomorphs
might have fed by absorbing nutrients directly
from seawater into their branched bodies.
So if nutrients like oxygen or organic carbon
were more available in slightly higher-up
water, for example,
the simulated rangeomorphs grew
taller and thinner.
That way, they could maximize the amount of
nutrients they could grab from the ocean.
Ocean chemistry was changing a bunch in the
Ediacaran,
so this kind of growth flexibility probably
helped rangeomorphs survive.
And the researchers think that at least one
of these big nutrient shifts might have let
organisms that were living side-by-side with rangeomorphs
grow bigger than ever before.
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