Download Chapter 28.3

Ch. 28.3 Formation of the
Solar System
• The solar system includes the sun and all
bodies revolving around the sun.
• Nebular theory—the entire solar system
formed at the same time. Sun and planets
condensed out of the same spinning
nebula.
Formation of the Sun
• Solar nebula—the cloud of dust and gas
that developed into our solar system.
• A shock wave hitting the nebula caused it
to start contracting 4 or 5 billion years ago.
• The sun formed in its center.
• 99% of the nebula’s matter became the
sun.
Formation of the Planets
• Planets formed in the outer regions of the
nebula, from small bodies called
planetesimals.
• They joined together through collisions to
form protoplanets.
• Protoplanets condensed into existing
planets and moons.
• The four inner planets contain high
percentage of heavy elements like iron.
• They couldn’t accumulate lighter gasses
because of their weak gravity and the
stripping action of the solar wind.
• The outer planets could maintain their
lighter gases, due to greater gravity and
further distance from the sun.
• They are known as gas giants.
Formation of the Earth
• Newly-formed earth was very hot due to…
• Retained heat from planetesimals
collisions.
• Heat from compression of outer layers on
inner layers.
• Radioactive decay heat.
The Solid Earth
• Heavier elements (mostly iron) flowed to
the center of the hot molten earth.
• Lighter, less dense elements forced to
outer layers.
• Eventual development of three distinct
layers…a dense iron/nickel core, a thick
rock layer called the mantle, and a thin
solid crust of less-dense materials.
The Atmosphere
• As the developing earth accumulated
mass and increased gravity, it attracted a
first atmosphere of hydrogen and helium
from the surrounding nebula.
• This was lost due to weak gravity and the
solar wind.
• A second atmosphere of mostly CO2 and
water vapor came from the earth’s interior
due to volcanic eruptions (outgassing).
• Sunlight converted ammonia gas into
nitrogen, and when green plants
appeared, photosynthesis caused oxygen
to slowly increase.
• An ozone layer developed and served as a
UV shield.
The Oceans
• When the earth cooled enough, water
vapor began to condense (3 to 3.5 billion
years ago).
• Rainfall filled up the ocean basins.
• Ocean water absorbed much CO2.
• By 1.5 billion years ago, the atmosphere
was similar to today’s.