The Birth of Planet Earth
About 4.7 billion years ago, dust and rocky blocks gravitated around the Sun and
formed spherical bodies of variable size (Fig. 2.1). Our home planet, Planet Earth,
must have begun to be formed with the accretion of dust and large blocks that
collided and agglomerated together. This agglomerated sphere attracted more
material from the stellar system and its gravitational forces generated heat so the
material began to melt. As melting occurred, particle differentiation began,
therefore the heavier components such iron (Fe), magnesium (Mg) and nickel (Ni)
sank into a magma pool towards the center of the planet while a silicate liquid
made up essentially of silicon (Si), aluminum (Al) and sodium (Na) rose towards
the surface.
There are many similarities between our planet and others in distant galaxies,
called exoplanets, because they are planets located beyond our solar system that
are orbiting around other stars. In terms of similarities, we could consider a planet’s density. In our own solar system, for instance, Mercury (5.42 g/cm
3 ), Venus
(5.25 g/cm
3 ) and Earth (5.52 g/cm
3 ) have similar densities when compared to that
of Mars (3.94 g/cm
3 ). The average density of a planet depends on its mass. The
bulk density of a planet is the ratio of the mass of a planet compared to its volume.
The variation in density between planets of similar size is related to a change in the
Fig. 2.1 The schematic representation infers the creation of planet Earth from our Solar Nebula.
The major-element compositional distribution with their relative abundance is shown (after White
2013)
24
2 Our Haven, Planet Earth
About 4.7 billion years ago, dust and rocky blocks gravitated around the Sun and
formed spherical bodies of variable size (Fig. 2.1). Our home planet, Planet Earth,
must have begun to be formed with the accretion of dust and large blocks that
collided and agglomerated together. This agglomerated sphere attracted more
material from the stellar system and its gravitational forces generated heat so the
material began to melt. As melting occurred, particle differentiation began,
therefore the heavier components such iron (Fe), magnesium (Mg) and nickel (Ni)
sank into a magma pool towards the center of the planet while a silicate liquid
made up essentially of silicon (Si), aluminum (Al) and sodium (Na) rose towards
the surface.
There are many similarities between our planet and others in distant galaxies,
called exoplanets, because they are planets located beyond our solar system that
are orbiting around other stars. In terms of similarities, we could consider a planet’s density. In our own solar system, for instance, Mercury (5.42 g/cm
3 ), Venus
(5.25 g/cm
3 ) and Earth (5.52 g/cm
3 ) have similar densities when compared to that
of Mars (3.94 g/cm
3 ). The average density of a planet depends on its mass. The
bulk density of a planet is the ratio of the mass of a planet compared to its volume.
The variation in density between planets of similar size is related to a change in the
Fig. 2.1 The schematic representation infers the creation of planet Earth from our Solar Nebula.
The major-element compositional distribution with their relative abundance is shown (after White
2013)
24
2 Our Haven, Planet Earth