ESS 101 EXAM Guide Questions and Answers
100% Correct. 2025/2026 Update
nebular hypothesis
1. supernova and formation of primordial dust cloud
2. condensation of primordial dust forms disk shaped nebular cloud rotating counter-clockwise.
3. proto sun and planets begin to form
4. accretion of planetesimals and differentiation of planets and moons (4-6 billion years ago).
5. existing solar system takes shape.
Evidence of nebular hypotheses
1. Planets and moons revolve in a counter-clockwise direction (not random)
2. almost all planets and moons rotate on their axis in a counter-clockwise direction.
3. planetary orbits are aligned along the suns equatorial plane (not randomly organized)
4. observations from Hubble telescope and radio astronomy indicate that other planetary systems
are forming from condensed nebular dust.
Terrestrial Planets
Close to the sun, dense, small/rocky, silicate minerals, metallic cores
Twelve earths would fit across the diameter of Jupiter.
Jovian Planets
Far from the sun, low density, large, gaseous (hydrogen, methane)
,Why does the earth and terrestrial planets have so little molecular hydrogen comprising
their respective atmosphere, yet the primordial dust cloud was mostly comprised of
hydrogen gas?
Hydrogen gas and helium gas escapes to space when put in our atmosphere.
Jupiter, saturn, and neptune maintain molecular hydrogen gas in the atmosphere because they
have high density.
Differentiated Earth
1. Iron Nickel Core (outer core liquid)
(inner core solid)
2. Fe-Mg silicate mantle
3. Fe-Mg-Al Silicate Crust (Ocean and Continental)
4. Oceans
5. atmosphere
How is the earth compositionally zoned?
Along a density gradient
How did the earth become compositionally zoned?
1. Accretion of planetesimals
2. initial heating due to kinetic energy of colliding planetesimals and compressional heating.
3. additional heating from radioactive decay.
4. iron catastrophe: melting temp of iron reached and dense iron nickel sink to core and lighter
materials are displaced outwards (including silicate rock of mantle and crust, ocean waters and
,atmospheric gases)
5. earth becomes compositionally zoned based on density (densest iron nickel in core-least dense
materials comprise the atmosphere) 500 mil yrs after the initial accretion process.
6. convective overturn in asthenosphere, mantle and outer core still occur today.
Why did the earth heat up and then rapidly cool during the differentiation process?
When earth was solid-heat gain was greater than the heat lost to space. This means that the
internal temperature rises until it exceeded the melting temp of oxygen and nitrogen until
exceeded iron nickel catastrophe. Earth is completely molten and then compositionally zoned.
When earth was liquid- convection-hot gas rises , after it became molten, the earth rapidly cooled
off and solidified.
Why does earth possess little evidence of its early accretion history?
Because of weathering, plate tectonics, moon has no atmosphere and biosphere.
Emissions from degassing of the earth during its differentiation.
h2o, co2, h2, he, n2
Where did molecular H and He escape to?
space
When did oxygenation of the atmosphere occur?
later following evolution of marine algae and plants that use photosynthesis to convert co2 to o2
as a part of their life processes.
What layers of the earth can be directly observed?
, crust and uppermost mantle.
Evidence of initial composition of the solid earth based on meteorite studies. There are two
major classes of meteorites that dominate collected samples. Carbon based meteorites are
much rarer, but indicate that the prescursor of life was present early on.
1. Metallic meteorites (iron nickel density 9.0-10 gm/cm3)
2. chondritic meteorites: Fe-Mg silicate, rocky, density is 3.0-3.3)
3. carbonaceous chondrites (rare)
What is earths average density?
5.5 g/cm3
How can average density of earth be inferred?
Based on gravitational properties and its effect on known masses such as orbiting satellites.
Density of earths crust?
2.6-3 g/cm3
density of uppermost mantle?
3.0-3.3 g/cm3
Based on the density information, what can you infer about the density of the lower mantle
and the earths core?
Density must be higher than the average.
What does the presence of the Earth's magnetic field provide evidence for?
100% Correct. 2025/2026 Update
nebular hypothesis
1. supernova and formation of primordial dust cloud
2. condensation of primordial dust forms disk shaped nebular cloud rotating counter-clockwise.
3. proto sun and planets begin to form
4. accretion of planetesimals and differentiation of planets and moons (4-6 billion years ago).
5. existing solar system takes shape.
Evidence of nebular hypotheses
1. Planets and moons revolve in a counter-clockwise direction (not random)
2. almost all planets and moons rotate on their axis in a counter-clockwise direction.
3. planetary orbits are aligned along the suns equatorial plane (not randomly organized)
4. observations from Hubble telescope and radio astronomy indicate that other planetary systems
are forming from condensed nebular dust.
Terrestrial Planets
Close to the sun, dense, small/rocky, silicate minerals, metallic cores
Twelve earths would fit across the diameter of Jupiter.
Jovian Planets
Far from the sun, low density, large, gaseous (hydrogen, methane)
,Why does the earth and terrestrial planets have so little molecular hydrogen comprising
their respective atmosphere, yet the primordial dust cloud was mostly comprised of
hydrogen gas?
Hydrogen gas and helium gas escapes to space when put in our atmosphere.
Jupiter, saturn, and neptune maintain molecular hydrogen gas in the atmosphere because they
have high density.
Differentiated Earth
1. Iron Nickel Core (outer core liquid)
(inner core solid)
2. Fe-Mg silicate mantle
3. Fe-Mg-Al Silicate Crust (Ocean and Continental)
4. Oceans
5. atmosphere
How is the earth compositionally zoned?
Along a density gradient
How did the earth become compositionally zoned?
1. Accretion of planetesimals
2. initial heating due to kinetic energy of colliding planetesimals and compressional heating.
3. additional heating from radioactive decay.
4. iron catastrophe: melting temp of iron reached and dense iron nickel sink to core and lighter
materials are displaced outwards (including silicate rock of mantle and crust, ocean waters and
,atmospheric gases)
5. earth becomes compositionally zoned based on density (densest iron nickel in core-least dense
materials comprise the atmosphere) 500 mil yrs after the initial accretion process.
6. convective overturn in asthenosphere, mantle and outer core still occur today.
Why did the earth heat up and then rapidly cool during the differentiation process?
When earth was solid-heat gain was greater than the heat lost to space. This means that the
internal temperature rises until it exceeded the melting temp of oxygen and nitrogen until
exceeded iron nickel catastrophe. Earth is completely molten and then compositionally zoned.
When earth was liquid- convection-hot gas rises , after it became molten, the earth rapidly cooled
off and solidified.
Why does earth possess little evidence of its early accretion history?
Because of weathering, plate tectonics, moon has no atmosphere and biosphere.
Emissions from degassing of the earth during its differentiation.
h2o, co2, h2, he, n2
Where did molecular H and He escape to?
space
When did oxygenation of the atmosphere occur?
later following evolution of marine algae and plants that use photosynthesis to convert co2 to o2
as a part of their life processes.
What layers of the earth can be directly observed?
, crust and uppermost mantle.
Evidence of initial composition of the solid earth based on meteorite studies. There are two
major classes of meteorites that dominate collected samples. Carbon based meteorites are
much rarer, but indicate that the prescursor of life was present early on.
1. Metallic meteorites (iron nickel density 9.0-10 gm/cm3)
2. chondritic meteorites: Fe-Mg silicate, rocky, density is 3.0-3.3)
3. carbonaceous chondrites (rare)
What is earths average density?
5.5 g/cm3
How can average density of earth be inferred?
Based on gravitational properties and its effect on known masses such as orbiting satellites.
Density of earths crust?
2.6-3 g/cm3
density of uppermost mantle?
3.0-3.3 g/cm3
Based on the density information, what can you infer about the density of the lower mantle
and the earths core?
Density must be higher than the average.
What does the presence of the Earth's magnetic field provide evidence for?
