The Place We Call Home: Part Three, Death and Rebirth

The Orion Nebula, a place where stars are born

The birth of our solar system arose from the death of a star. A nebula is formed from clouds of helium and hydrogen left over from the big bang, and more crucially (for us) the heavier elements that are formed in fusion reactions inside a star, and during the colossal explosion at the end of it’s life. It’s well worth taking just a moment to do a quick google search for images of nebulae, they are among the most beautiful things ever photographed.

 

These elements began to form our solar system when a small part of this giant nebula underwent a gravitational collapse. Most of collapsing mass began to form our proto sun at the centre, whilst the rest of the mass flattened to form an accretion disk – out of which came our planets, moons and other small solar system bodies.

A rendition of an accretion disk

These clouds of dust and gas formed rings around the early sun. The heavier elements formed the inner rings of the accretion disk, whilst the volatile elements formed the outer rings. The dust and ice then collide together to form larger clumps known as planetesimals.

 

Through constant collisions these planetesimals gradually formed a potato-shaped proto-Earth. Eventually the core of the proto-Earth heats up and becomes soft. Continuously growing through collisions, the proto-Earth is shaped by gravity into a sphere, and the interior of the Earth separates into a core, and a mantle. The other planets in our solar system were formed in a similar way.

A rendition of Earth's catastrophic collision with Thea

 

Soon after the Earth was formed it suffered a catastrophic collision with another Mars-sized planet called Thea. The debris from this collision is what eventually came together to form our moon.

 

It is through the violent death of a star, and a world of deadly collisions that formed the place we call home. From all this death and destruction came a planet upon which life would eventually flourish. At the start of things however, the Earth was a hell-like furnace of volcanoes and collisions – not the kind of place you would imagine turning into the lush green and blue haven we inhabit today. In the next couple of articles I will explore how the planet slowly became more and more ‘hospitable’, but that would be meaningless without looking into the most interesting events of all; the origin of life.

 

In the early days of our planet, the view from my window might have looked something like this:

A Hadean landscape

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