Timeline of the Nebular Theory
o About 15 billion years ago the universe
was formed from a primordial atom
that consisted of all the matter and
energy that exists today.
o About 4.6 billion years ago shockwaves
caused the solar nebula (dust and gas
that developed into our solar system)
to contract.
o As the solar nebula condensed its
temperature increased and began
glowing, forming the protosun (the
protostar for our solar system).
o The protosun continued to become
hotter and hotter until hydrogen
started fusing into helium, at which
time the sun (a typical star) was
formed.
o 1% of the material that is not part of
the sun began to condense and form
small bodies of matter called
planetesimals.
o The planetesimals joined together
through collisions and the force of
gravity to form larger bodies called
protoplanets. Protoplanets acted like
giant magnets, pulling more
planetesimals towards themselves.
o The four planets close to the sun
(Mercury, Venus, Earth and Mars)
contain heavier elements, such as iron.
o The four further planets (Jupiter,
Saturn, Uranus, and Neptune) are made
of lighter elements like hydrogen and
helium and frozen gases like ammonia.
o Some of the protoplanets became
moons, small bodies that orbit the
planets
o The solar system consists of our sun
and all the bodies that orbit it
o When Earth first formed it was very
hot. Gravity pulled heavier elements to
the core (made of iron nickel).
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The lighter elements remained in the
outer layers like the crust. This is
what created the layers of Earth!
Earth’s first atmosphere was lost to
solar wind.
About 3.5 billion years ago Earth’s
second atmosphere was formed, a
result of out-gassing from volcanic
eruptions which released mostly water
vapor and carbon dioxide. Sunlight
turned water vapor and ammonia into
nitrogen and hydrogen.
Earth’s oceans were formed about 3
billion years ago when water vapor
condensed and it rained. The oceans
absorbed much of the carbon dioxide
of the early atmosphere.
About 1.5 billion years ago Earth’s
third atmosphere was created after
cyanobacteria and early plants
developed. These organisms took
carbon dioxide and turned into oxygen.
Some oxygen combined into ozone,
creating the ozone layer which shields
organisms from UV radiation.