How was Earth formed?

Big Bang Theory 13.7 billion years ago 13.7 billion years ago Creation of all matter Creation of all matter Hydrogen and Helium first Hydrogen and Helium first More complex elements evolved through time More complex elements evolved through time

The Nebula Hypotheses Nebula - Interstellar cloud of dust, hydrogen, helium, and other ionized gases.

The Nebular Hypothesis The solar system formed from a collapsed nebula 1734 by Emanuel Swedenborg Observations support this idea

Pillars of Creation

Nebulae: step 1 Gas (98%) and dust (2%) Rotates and is held together by gravitational force

Step 2: The Nebula collapses The collapsed mass forms a proto-sun due to gravitational force Contraction increases speed of rotation: collapse

Step 3: sun is formed, disk cleared The disk is “cleared out” due to the immense amount of energy released. Sun is formed Dust and gases cool and condense in defined orbits around the sun

Nebula hypothesis: step 4- planet formation Temperature differences with respect to distance from sun Closer = HOT!, iron and other heavy condense Farther = cooler, hydrogen, water condense material collides and accretes forming planetesimals (small planets)

Evidence: Orion Nebula Third star down on Orion’s belt 100 light years across Reflection of dust and hydrogen

Evidence: Collapsed nebulae discs found in the Orion nebula Gaseous disks are circling proto-suns times larger than our solar system About 153 protoplanetary disks found in the Orion Nebula

EarlyEarly Earth Homogenous Very hot

Bombardment From Space For the first half billion years of its existence, the surface of the Earth was repeatedly pulverized by asteroids and comets of all sizes One of these collisions formed the Moon

Formation of the Moon The Giant Impact Hypothesis - 50 million years after creation of Earth, a planet about the size of Mars collided with Earth First proposed about 30 years ago, but it took calculations by modern high-speed computers to prove the possibility

Formation of the Moon This collision had to be very spectacular! A considerable amount of material was blown off into space, but most fell back onto the Earth

Formation of the Moon Part of the material from the collision remained in orbit around the Earth By the process collision and accretion, this orbiting material coalesced into the Moon The early Moon orbited very close to the Earth

Compositionally distinct layers Physically distinct layers Segregation of elements: gravitational force Remember: the liquid outer core with the Earth’s rotation produces the magnetic field.

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