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Ch. 28.3 Formation of the Ch. 28.3 Formation of the Solar SystemSolar 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 SunFormation 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 PlanetsFormation 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 EarthFormation 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 EarthThe 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 AtmosphereThe 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 OceansThe 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.