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Hello, welcome to Up and Atom.
I'm Jade.
Did you know that the Sun gets brighter
and hotter over time?
In about 5 billion years, it will be so big
that it'll engulf Mercury, Venus and potentially even Earth.
Sad.
It naturally follows then that billions of years ago,
the Sun was dimmer.
Let's jump back about 3.5 billion years.
On cosmic timescales, our Sun was just a baby
shining at only about 3/4 of the brightness it is today.
But what does a smaller dimmer Sun mean for Earth?
Well, it means it wouldn't be as warm as it is today.
In fact, 3.5 billion years ago,
the Earth should have been below freezing temperatures.
In scientific terms, it would have been a snowball Earth.
But you know what else was happening
about 3.5 billion years ago?
Life.
Around this time, life was beginning to form on our planet.
And what is that generally believed that needs to be present
for life to exist?
Oh, wait.
(clock ticking)
(gasping)
Liquid water.
Have you spotted the problem?
How could liquid water exist on a snowball Earth?
Or did life somehow managed to form
under the cold harsh conditions of a snowball Earth?
As Dr. Malcolm says...
- Life finds a way.
- But how did you find your way?
Let's go digging for some answers.
Zircon grains and features in emergent crust
indicate that billions of years ago
the Earth actually did have liquid water.
So these aren't really zircon grains
because they're difficult to acquire,
but let's just pretend that they are.
By studying the chemistry of ancient zircon grains
found in Western Australia,
scientists have found that it's likely they formed
in the presence of liquid water.
On top of that, ancient rock
in the Barberton Greenstone Belt in South Africa
exhibits water-like ripples in the sandstone.
Another piece of evidence for liquid water.
So the general consensus among scientists
is that 3.5 billion years ago,
the Earth did have liquid water
and was actually pretty toasty.
As a consequence, life was able to evolve and flourish
on our young little planet.
But this brings up another interesting question.
How could the Earth have been warm
while the young Sun was faint?
This is called the faint young Sun paradox,
first introduced by astronomists Carl Sagan
and George Mullen in 1972.
How was the Earth warm enough
to sustain life and liquid water
when the Sun wasn't giving off enough heat?
I would never in a million years have guessed the answer.
The most likely answer that scientists agree on
is volcanoes and green house gases.
Greenhouse gases, fine, but volcanoes?
This is a weird answer, right?
But that's the cool thing about science,
you wind up with the most unexpected answers.
It turns out that the early Earth
had a lot of tectonic activity.
Slabs of the Earth, upper mantle and crust,
collided with one another causing earthquakes,
mountain ranges and volcanoes.
When a volcano erupts or releases gas,
it emits a ton of greenhouse gases,
including carbon dioxide.
As we know from human emissions,
carbon dioxide can drastically change the climate
and warm the Earth,
especially when released in high amounts.
Billions of years ago
during what we now call the Archean Eon,
it's believed that volcanic activity
was much more common than it is today.
If there were a lot more erupting volcanoes,
a lot more carbon dioxide and greenhouse gases
would be released keeping our young Earth nice and toasty.
But there's more.
Have you ever wondered how all the land on Earth formed?
Honestly, before making this video
I had never even thought about it.
It wasn't even like I was like, "Oh, how did that happen?
I don't know."
The question had never even entered my mind.
And the answer is partly, volcanoes again.
Lots of the land shaping out continents
was formed through tens of thousands of volcanic eruptions.
Each one releasing magma from the Earth's mantle
and lower crust
and cooling to form exposed land at the surface.
This process happened over billions of years.
And back in the Archean Eon,
it's estimated that only two to 3%
of the Earth surface was land
compared to the almost 30% we have today.
So what does this have to do with anything?
Well, have you ever noticed how,
if you wear black on a hot day,
it tends to make you even hotter?
This is because black is good at absorbing the Sun's heat.
You to wear white on a hot day
because it reflects more sunlight.
You probably know from experience
that some surfaces absorb or reflect
more sunlight than others.
We can see this effect in a cool way
in this picture I found on Reddit.
A perfect leaf shape melted in the snow.
How did this happen?
The dark leaf absorbed more heat from the Sun
than the ice around it,
heated it up and melted the ice below it.
The measure of a surface's ability to reflect light
is called albedo.
The more light it reflects the higher its albedo.
The word sounds so much like libido, it's weird.
A white T-shirt has a higher albedo than a black T-shirt.
This leaf had a lower albedo than the ice around it.
Different areas of the Earth surface
have different albedos.
For instance, white deserts have a pretty high albedo
reflecting lots of sunlight,
and oceans have a pretty low albedo
absorbing lots of sunlight.
Since the surface of the Earth during the Archaean Eon
would primarily be composed of water
and dark black rock from volcanoes,
it would cause the planet to have a much lower albedo
than it does now.
As such the Earth would have the ability
to absorb more sunlight and heat up.
In short young Earth had a lower albedo than older Earth
so it could absorb more of the Sun's limited rays.
So there it is.
We've solved the paradox.
Early Earth was able to sustain liquid water
and therefore life because volcanic activity
led to more greenhouse gases
and decreased the albedo of the Earth.
Volcanoes get a pretty bad rap,
but if it weren't for them you might not be here today.
And now perhaps the most important question of all,
who cares?
What was the point of this entire video?
Well, understanding the early Earth and Sun
isn't just important for understanding
how life on our planet evolved,
but for understanding how life might evolve
on other planets too.
Let's look at our nearest neighbor, Mars.
Sitting at an average temperature
of a cool negative 60 degrees Celsius,
Mars is currently a cold harsh place.
If the Sun was fainter in the past,
it's expected that Mars would have been even colder
billions of years ago.
However, we've found river channels
and crater lakes on Mars.
So just like Earth, Mars may have once been a warm planet
with liquid water.
And if Mars had liquid water
could life once have existed on the red planet too?
Answering this question might take a little perseverance.
As of February 18th, 2021,
NASA's Perseverance rover is the ninth mission
to land on Mars.
Perseverance landed in the Jezero Crater
with the goal of searching
for signatures of early life on Mars.
Through collecting core rock samples,
scientists hope that Perseverance will allow
for the first ever samples of Mars
to be brought back to Earth to be studied,
allowing us to learn if we had any living cosmic neighbors
in the past.
Ultimately the more we understand about the relationship
between the early Earth and Sun,
and the atmospheric and geological processes involved,
the more we can understand about ourselves,
life and other potentially habitable worlds.
If you enjoyed this episode
and are fascinated by space and the solar system in general
may I recommend a book?
I've been listening to "The Planets"
by professor Brian Cox and Andrew Cohen.
It's about the history of our solar system
and why the planets are the way they are.
We tend to think of our solar system
as kind of always being the way it was
but it was actually very chaotic
and so much of how it is, is just random chance.
Like the size of Mars
is largely due to the orbits of Saturn and Jupiter,
Mercury, Earth, Venus and Mars
all formed in pretty much the same way
yet because of the fragility of the solar system,
they all turned out so differently.
It made me even more amazed
at the fact that Earth just happens to be right for life.
It's also an amazing feat of humanity
that we were able to figure out so much
from basically studying rocks.
If you'd like to learn
about the interconnectedness of our solar system
and how we came to be here
you can listen to "The Planets" for free
by signing up with Audible,
using the link audible.com/upandatom.
Audible is an audio book service
with thousands of titles, guided fitness,
sleep tracks, and more.
I read a lot to make these videos.
So sometimes it's nice to just sit back
and let someone read to you,
in the car, on a walk, wherever.
If you'd like to support the channel
and make time for more learning in your life,
sign up to Audible with the link audible.com/upandatom
for a free 30-day trial
where you'll receive your first audio book completely free.
I really would recommend "The Planets"
but of course it's totally up to you.
Thanks for tuning in and I'll see you in the next episode.
Bye.
(upbeat music)