Our Universe 3D Page #2

and ignites matter,

continuing the process of star birth.

In some cases,

the collected mass isn't big enough,

and the young sun fails to

keep a nuclear reaction running.

The result is a brown dwarf,

an astral body

in between a sun and a huge planet.

But if the ignition succeeds,

another chain reaction is triggered,

one that may ultimately lead

to the creation of life.

The gravity of the newborn sun sets

the matter around it in motion.

Nearby portions of the nebula are pulled in,

and begin to spiral around the sun.

A protoplanetary disc is formed.

As the matter whirls about,

a process of accretion begins.

This is an effect of zero gravity that

causes particles to cling together.

That way,

bigger masses of material start to form.

As these become larger,

they grow into asteroids.

Directed by the sun's

gravitational attraction,

the asteroids move

around at high speed.

They crash into each other repeatedly,

resulting in the formation

of even bigger masses of rock.

Eventually, some of them grow large enough

to have a significant gravitational pull,

and, therefore,

pick up more and more material.

Over time,

this process leads them to become planets.

Some of these planets even develop

an atmosphere by collecting particles of gas

floating through the surrounding space.

And our Earth was made the same way.

After a core had formed from materials

of our sun's protoplanetary disc,

the young Earth was constantly bombarded

by asteroids and other celestial bodies.

Back then, Earth was much closer to the sun,

and was very, very hot.

Its surface was made of

one big ocean of lava.

There was no solid crust, no land,

not even water,

just heat, lava and fire.

Comets kept crashing

into that brooding surface,

raising the temperature with every hit.

Eventually, the young planet suffered

a massive collision with something huge,

another planet in the making.

The impact was so severe,

it ripped off a part of the Earth's mantle.

The debris then formed a ring around Earth.

Again through the process of accretion,

this rubble formed the moon

over the course of millions of years.

Earth, on the other hand, was thrown into a

furious rotation by that horrendous impact.

It was spinning so fast,

a day lasted only six hours.

After hundreds of millions of years,

it gradually slowed down again.

Also, the contents of the sun's

protoplanetary disc were finally used up,

having formed the other planets and moons.

Accordingly,

the astral bombardment decreased,

so the surface could cool off.

This led to the formation

of a solid crust of stone.

Still, there were frequent

volcanic eruptions.

They spat out lava and gases,

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