From rocks, stars and asteroids – this is how we answered the question: when did the Earth form? With a glimpse of the Hadean Epoch
Fire, molten cores and cosmic collisions. Our planet, Earth, was born in an amazing period of solar system formation, a few million years after our sun first ignited.
It’s a complex and dynamic world. As far as we know, the only place where you can reach out and touch life, at least for now. And its history spans billions of years – see exactly how Earth formed.
Understanding how and when Earth formed not only tells us about our own origins but also forms the basis of our understanding of science. And it gives us a glimpse into planetary formation and evolution in the entire universe.
When did Earth Form?
The Earth formed approximately 4.54 billion years ago. Just a few tens of millions of years after the sun formed from a swirling mass of debris that collapsed under its own gravity and ignited our star around 4.6 billion years ago. Also see when the solar system formed.
Born from awesome cosmic collisions (known as planetary accretion) the early Earth would have been a floating ball of magma. With oceans of lava, no discernible landmasses and no air to breathe. Get the full picture of how Earth formed.
And it would have stayed that way for almost half a billion years, during the period known as the Hadean (named after Hades), before finally cooling enough to begin its evolution into the world we know today.
How do we Know When the Earth Formed?
Scientists determine the age of Earth with a range of processes.
Firstly, we can use telescopes to observe other stars, solar systems and planets as they form. This lets us draw conclusions about how our own solar system formed.
Then, we use radiometric dating – a process that measures the decay of radioactive elements in rocks. (Which act as a natural clock, ticking away since the Earth’s formation.)
By dating meteorites, parts of the Earth itself and even the moon, which we’ve seen all form at roughly the same time when we observe other solar systems forming, scientists can estimate the age of the Earth.
Get the full picture with a complete breakdown of how we know when the Earth formed.
So, how old is the Earth then?
Earth is about 4.54 billion years old. To comprehend such a vast span of time, geologists divide it into eons and eras. The first period of Earth’s history is known as the Hadean (4.5–4 billion years ago), followed by the Archaen (4–2.5 billion years ago). Then comes the Proterozoic (2.5bn –542 million years ago) and finally the Phanerozoic (540 million years ago – today).
How Exactly did the Earth Form?
In simple terms, Earth formed through the process of accretion. See how our solar system formed.
Initially, Earth was one of the rocky bodies that formed inside the solar nebula (a cloud of gas and dust swirling around our newborn sun). Particles collided and stuck together, gradually building larger bodies – planetesimals.
The early Earth was one of these. And, over time, planetesimals collided to form protoplanets. Then as more material accreted, the process led to the formation of planets, including the Earth.
The young Earth went through a phase of intense heat and melting, allowing heavier elements to sink to the centre, forming its core, while lighter materials formed the crust. This is what gave us plate tectonics and our magnetosphere – crucial to the evolution of life.
See exactly how the Earth formed.
What was the early Earth like?
Scientists believe the earliest body we might call proto-Earth may have been only a 10th of its current size. And that it would have taken at least 10 or so mega collisions with other protoplanet-sized objects to build its current mass. (See the research here.)
Earth in the Hadean would be almost unrecognisable. The entire planet would have had a molten surface – hence the reference to Hades (“hell” from Greek mythology). It would have had a crushing atmosphere of hydrogen and helium – no oxygen. And, over time, volcanic outgassing introduced water vapour, carbon dioxide, and other gasses.
The Moon likely formed when another Mars-sized body collided with Earth, ejecting debris that eventually coalesced into our Moon (known as the Moon-forming Giant Impact). And then a barrage of asteroid impacts known as the Late Heavy Bombardment would have struck around 4 billion years ago, reshaping the Earth’s surface.
Over time, Earth’s magnetic field (our protection from deadly solar radiation) would have formed. As well as plate tectonics, the movement of Earth’s surface that creates continents and oceans.
The most amazing thing, though, is that even in that first hellish time of Earth’s birth, the basic elements for life were already present.
Watch: Some Awesome Documentaries on the Earth’s Formation
The Whole History of the Earth and Life
One of my personal favourites, this non-commercial, mainly YouTube-only documentary is a project by Japanese creator @KarouGreenEmerald, based on the research findings of the Tokyo Institute of Technology’s Professor Shigenori Maruyama and the Hadean Bioscience Project, which proposes some new theories on the formation of Earth, development of life, evolution as well as some future-casting.
History of the Earth
National Geographic’s 2011 Yavar Abbas documentary gives a pretty exciting overview of how the solar system and Earth may have formed. (Again, no purchase links for this title.)
Birth of the Earth
Episode 9 of Season of National Geographic’s Naked Science. (Sorry, I can’t find it available for purchase anywhere.)
Earth’s Formation
An 18-minute look at the planet’s birth by YouTube channel @HistoryoftheEarth.
Catastrophe Episode 1
Another 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.
