The Formation Of The Solar System And The Hadean Earth Flashcards
What is the age of the solar system?
4567Ma
What is used to date the solar system?
Meteorites such as the Allende meteorite can provide information about the chemical composition of the Universe when they were created.
How did the solar system form, according to nebular theory?
The sun and planets formed by gravitational collapse of interstellar gas and dust (molecular cloud) at about the same time.
What is the principle of Uniformitarianism?
A concept that suggests geological processes (erosion, sedimentation and volcanic activity) operated in a similar manner throughout Earth’s history.
How does the surface elevation of the Earth vary- where are the highest and lowest points?
Variations are due to tectonic activity, erosion, volcanic processes and sedimentation over millions of years. The highest points are mountain summits (such as Everest) and the lowest points include deep oceans (Challenger deep)
How can we study the Earth’s interior?
Seismic waves, volcanic activity, density and gravity measurements, Earth’s magnetic field and meteorite composition
Why study meteorites?
They provide evidence of the age of our solar system and it’s chemical composition
What is the internal structure of the Earth?
Solid inner core, molten outer core surrounded by the mantle, encased in the crust
What are the key differences between the internal layers (e.g., chemical and mineral composition, density etc)?
More metals within the core, and more silicates within the mantle due to separation of densities, they’re also immiscible.
What are the differences between oceanic and continental crusts?
The thickness (7km v 30km), composition (basaltic vs granite) and density (oceanic density higher)
What is the Moho and how does it vary?
The boundary between the Earth’s crust and the underlying mantle, it varies with crustal thickness and tectonic activity
Why is the inner core solid?
Extremely high pressure
What are the 3 principle subdivisions of the Precambrian and the age of the boundaries between them?
The Hadean (4567Ma-4000Ma)
The Archean (4000Ma-2500Ma)
The Proterozoic (2500Ma-541Ma)
What defines the start and end of the Hadean?
The Hadean begins with Earth’s formation and ends when the last rock can be dated back to.
What proportion of earth history does the Hadean represent?
13%
What is the age of the Earth?
4567Ma
How did the early Earth grow in size(what are the stages)?
Planetary accretion leading to planetesimal formation, runaway growth leading to planetary embryo forming due to gravitational attraction
What is a planetesimal?
Objects up to 100km in diameter, formed by accretion which go on to form planets
What processes caused dust and condensing material to accrete into planetesimals? How did planetesimals grow into the inner planets of the solar system?
Gravitational attraction, which then lead to the runaway growth of planetesimals into planetary embryos
When and why did the Earth’s interior core and mantle separate? What was the source of heat that lead to melting of the Earth?
Collisions of the early Earth lead to lots of energy being released which was hot enough to form a molten magma Earth, the metals and silicates within then separated due to metals having a higher density and the material being immiscible.
What is the age of formation of the moon?
Approximately 4500Ma (67 million years younger than Earth)
How did the moon form?
A giant impact between Earth and Theia (another protoplanet), which vaporised the mantles of both bodies, however the debris remained in circumterrestrial orbit of Earth, which accreted to form the moon
What is the age of oldest zircon and where are they found?
The oldest known zircons are 4.404 billion years old and were found in the Jack Hills of Western Australia.
What was the composition of the Hadean crust?
Primarily basaltic, high-temp minerals and high volcanic activity
What was the tectonic style of the Hadean earth and early Archean? What is meant by a ‘stagnant lid’?
Hadean Earth only contained one tectonic plate, a single shell, which is referred to as a ‘stagnant lid’
By the end of the Hadean, the Earth had a primitive atmosphere and early oceans. Contrast these with the oceans and atmosphere today. What were the major gases in the early atmosphere? What gas was not present that is common in the current atmosphere?
The Hadean atmosphere had high levels of greenhouse gases such as CO2, CH4, CO and H2O, in much higher concentrations than can be found today. There was no oxygen present yet. The early oceans went through cycles of being warm (allowing carbonated rocks to form) then becoming icy as Earth cooled, before another collision caused heating again.
When did liquid water form at the Earth’s surface?
The presence of quartz inclusions in zircons, tell us they must have formed from pre-existing basalt melting in the presence of liquid water, so water was liquid during the early Hadean (4.4 Ga)
What was the fate of the early atmosphere of the Earth?
Cooling and condensation, chemical reactions, development of life, the great oxygenation event and atmospheric escape
What was the character of the Hadean landscape?
High levels of volcanic activity, many impacts and large volumes of water
What was the role of impacts in the early Earth?
Maintained higher enough temperatures for liquid water, which then cooled molten rock so form carbonated rocks in the ocean, which then lead to oceans becoming icy, so impacts were needed to raise the temperature again
