Formation of the Solar System The Nebular Hypothesis

Formation of the Solar System

The Nebular Hypothesis • States that the sun and the planets condensed at about the same time out of a rotation cloud of dust and gas (SOLAR NEBULA) • The solar nebula began to increase in temperature and rotation and flatten into a disk. • The sun consists of 99% of all matter that was contained in the solar nebula.

The Orion Nebula 1500 LY from Earth

Accretion • One theory that describes how asteroids and planets formed. • As material moved around our young Sun (protosun), the dust grains collided and began sticking together to form larger rocks. • Those rocks collided with other rocks and were held together by gravity or broken off into pieces. • Eventually these rocks combined into larger and larger bodies, and eventually formed the plantets.

Formation of Planets • PLANETESIMALS- Small bodies from which planets originated in early formation • PROTOPLANETS- Formed from collisions between planetesimals and through the force of gravity. • Planetesimals and protoplanets formed by ACCRETION

Formation of Solid Earth

Earth was HOT !!!!! • 3 SOURCES OF ENERGY CONTRIBUTED –Energy from planetesimal collisions –Energy produced by weight of outer layer on inner layers –Radioactive materials very abundant when Earth formed and emit high-energy particles

DIFFERENTIATION • Denser materials ( like molten iron) sank to the center of the Earth and less dense materials forced to the outer layers. • Earth formed three distinct layers.

EARTH’S ATMOSPHERE • Atmosphere formed because of differentiation • Less dense gases, H and He • rose to the surface • Earth’s gravity was too weak to hold onto gases • Earth’s magnetic field not fully developed

Outgassing frequent volcanic eruptions releasing H 2 O vapor, CO 2, N, Methane (CH 4), Sulfur dioxide (SO 2), and ammonia(NH 3) This formed our new atmosphere

And then………. • Radiation from sun cause ammonia and water vapor to break down • H- escaped to space • O- formed ozone O 3 that shielded Earth from UV radiation from sun

Earth’s present atmosphere • Organisms developed such as cyanobacteria and early green plants (using CO 2, releasing O 2 ) • Amount of O 2 increased (2 billion yrs ago this increased rapidly) • Composition of atmosphere 2 billion years ago similar to present day

EARTH’S OCEANS • Theory: icy bodies like comets collided with Earth and the water from them became part of our atmosphere • Earth cooled vapor formed water and collected • First ocean likely fresh water • Over millions of years runoff from rainwater dissolved chemicals from rocks and carried them to oceans • Water cycle through evaporation increased salinity in the oceans over time.

Ocean’s effects on atmosphere • Affect temperature by dissolving CO 2 and affected early climate helping to heat the atmosphere • The concentration of CO 2 in the atmosphere has increased and decreased over time causing warmer and cooler climates