About 4.568 billion years ago the most unique planet in our solar system was born.
Not too close or too far from the sun. With enough mass to hold onto its oceans, a protective magnetosphere to block harmful solar radiation and, eventually, an atmosphere with oxygen to breathe.
The Earth is the only place we know of with life (so far). It gave rise to some of the most awesome creatures you could ever imagine. And, as far as we know, the only species intelligent enough to ask: but how did this all get here?
This is perhaps one of the greatest stories ever told.
The story of how the Earth formed.
How Earth Formed – Step by Step
Step 1: The Birth of our Solar System
Our story begins in a vast cosmic cloud of dust and gas – the solar nebula. 4.6 Billion years ago on a quiet arm in the Styx of the Milke Way galaxy, this cloud, under the relentless pull of gravity, collapsed in on itself. (See when the solar system formed.)
And in the centre, under crushing forces, a star was born. Our sun.
Around it, a sea of swirling dust, gas and ice. And somewhere in that crazy and cataclysmic celestial nursery, a planet with a very special destiny began its journey – the Earth.
See exactly how the solar system formed.
Step 2: Formation of Proto-Earth
In the chaos of the young solar system, particles collided and stuck together, forming larger bodies. Among these was the proto-Earth, a young planet in the making, growing through violent impacts and the accumulation of matter.
See exactly when Earth formed as well as how we know when Earth formed.
Step 3: Birth of the Moon
One of the most pivotal moments in Earth’s history was its hypothesised colossal collision with a Mars-sized body, affectionately nicknamed “Theia”. (There were lots of other planet-sized bodies around Earth in the early solar system. And the Earth wouldn’t be able to sustain life if it hadn’t collided with thousands if not millions of other bodies during its birth.)
According to the Great Impact Theory, the cataclysmic collision event with “Theia” cast a cloud of debris into orbit, which eventually coalesced to form our Moon.
This newly formed Earth-Moon system then began a complex dance. The Moon’s gravitational pull influenced Earth’s rotation, leading to longer days and stabilising the tilt of our planet’s axis, a key factor in developing our climate. Not to mention influencing the Earth’s tides – all vital for creating life.
Step 4: The Molten State of Early Earth
But Earth was no paradise, yet.
As the early Earth continued to grow through constant bombardment, its surface was a fiery ocean of magma. Radioactive decay and the heat from relentless impacts kept the planet in a molten state (literally a ball of lava floating in space), for millions upon millions of years. A far cry from the blue and green orb we know today.
This is the start of the period in Earth’s history known as The Hadean (named after Hades, the Greek god of the underworld or hell). A time when the heart was a lava ball for some 500 million years.
And, like any good ball of lava, the Hadean Earth didn’t allow any normal rocks to form on its surface. It simply melted them away. Over and over again.
That’s why none of the first continents are left on the surface of the Earth today. As soon as some rocks had boiled up and started cooling, the molten planet would have just melted them and subsumed (reabsorbed) them.
To this day, no intact rocks survive from the Hadean – only a few microscopic fragments in one specific place in Australia. (Note: some people believe that there are some Hadean rocks in Canada, but that’s disputed since tests show they’re much younger, originating from the Archaen era).
Step 5: Differentiation and Formation of Earth’s Layers
In this molten state, heavier elements like iron and nickel sank towards the planet’s core.
Lighter silicates rose to form the mantle and crust. This process, known as differentiation, gave Earth its layered structure – a core, mantle, and crust.
This inner structure would be vital for creating the magnetosphere that would protect Earth’s atmosphere. Mars, for example, doesn’t have layers and a core, that’s why its atmosphere (which it definitely had once) got blown away into space.
The layers would also be vital for creating one of the most fundamental geological processes that allow Earth to harbour life. Plate tectonics.
Step 6: Formation of the First Oceans and Atmosphere
Eventually, the Earth began to cool. Water vapour from volcanic outgassing condensed to form the first oceans. Though they would have been extremely toxic. So rich in heavy metals, it couldn’t have sustained life until plate tectonics kicked in.
What’s more, Earth’s early oceans would have been covered in an extremely thick layer (hundreds and hundreds of meters) of deadly liquid carbon.
Of course, you wouldn’t have been able to breathe on this version of Earth. There was no oxygen, yet. The first atmosphere would have been hydrogen and helium. And, once it started cooling a bit, maybe some carbon, ammonia and methane.
After some volcanic activity, you’d have some nitrogen, loads of extra carbon and maybe a bit more hydrogen. It would still be billions of years before the Earth had any oxygen to breathe.
Step 7: The Late Heavy Bombardment
While the Earth was initially formed from truly massive collisions, like the one that formed the moon (see step 3), we have to remember it was constantly being pelted by millions upon millions of asteroids and comets, nearly all the time in the Hadean.
In fact, science says that when the Earth was molten, virtually all of its iron would have sunk into the core. Meaning that there should not be iron accessible for us humans to mine on the Earth’s surface today. But there is iron on Earth’s surface. So what gives?
The only explanation is that the iron we use today didn’t come from the Earth. It was delivered here by asteroids and especially comets from the outer solar system after the Earth had cooled enough to stop being a molten ball of lava – and that only happened in the Archaen era.
Earth’s also not supposed to have water, if you consider how the solar system formed. (Earth’s inside the dry part of the Snow Line, meaning there shouldn’t be any water here.) So that too must have been delivered by comets – just imagine, for a second, how many comets it would have taken to deliver all the water in all the oceans to our planet!
But it wasn’t over yet.
Towards the end of Earth’s Hadean and into early Archaen stages (4.1 to 3.8 billion years ago), Earth and its Moon faced a period of intense meteorite activity known as the Late Heavy Bombardment. This era left indelible marks on both bodies, with craters on the Moon still visible as a testament to this turbulent time.
Step 8: Setting the Stage for Life
These initial conditions, though hostile by our current standards, laid the foundation for life.
Violent as the heavy bombardment was, it delivered important minerals, metals and life-giving water to our planet – enough water to fill all our oceans.
And when plate tectonics kicked in, it helped clean the oceans. It pulled all those poisonous heavy metals down into the deep mantle and began clearing away the toxic liquid carbon layers floating atop the oceans, turning them into more hospitable waters.
The immense heat and radiation from inside the Earth, though deadly, was exactly the kind of energy inorganic matter needed to start collecting into organic compounds – the building blocks of life.
And the moon’s gentle, stabilising gravity was just enough to cause tidal wet-and-dry cycles, so those organic compounds could collect together and start building barriers around themselves so the first proto-cells could be born.
The fiery, hellish Hadean Earth might not seem like a very hospitable time. But it was absolutely crucial to preparing the Earth to harbour and sustain the first stirrings of life.
How do we know when the Earth formed?
Scientists determine the origin and age of the Earth through observation and theories we can test. Firstly, we can see quite a few star-forming regions elsewhere in the galaxy and have been studying them for a while.
This allows us to build quite complex models for how things might have come to be. And, of course, we can actually date any rocks we find – on Earth, the moon and even asteroids and meteors. We can even tell the age of the sun just by looking at it closely.
Get the full story about how we know when the Earth formed.
Watch: Some Awesome Documentaries on How Earth Formed
They’re not always 100% accurate because we make new scientific discoveries all the time. But documentaries at least deliver the gist of the information in a fun and engaging way. Just click play, hit full screen if you want to and check out hours’ worth of awesome documentaries on our planet’s birth, right here…
Birth of the Earth
Episode 9 of Season of National Geographic’s Naked Science. (Sorry, I can’t find it available for purchase anywhere.)
The Story of Earth and Life
National Geographic’s 2011 Yavar Abbas documentary gives a pretty exciting overview of how the solar system and Earth may have formed. (Sorry, can’t find purchase links for this title.)
Catastrophe Episode 1
One of my favourites, the Catastrophe series with Tony Robinson is also known as Prehistoric Disasters, and you can find it here on Amazon Prime.
PBS Eons: A Brief History of Geologic Time
Some of the best short science videos are from PBS Eons on YouTube – they’re well-researched and recommended.
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Enjoy the journey of discovery through Earth’s ancient past, geology, big ideas and, of course, awesome prehistoric life.
