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.