Lecture 9: Earth Formation, Hadean, and the Archean

This flashcard set focuses on the formation of our solar system and key events during the Hadean and Archean eons. It covers the origins of the solar system, early Earth formation, and significant geological and biological developments in the periods of the Hadean and Archean Eons.

Nebular Theory

Explanation of solar system formation from a collapsing nebula, leading to the Sun and planets.

Acasta Gneiss

The oldest intact rock.

Archean Eon

A time period in Earth's history, about 4 billion to 2.5 billion years ago, when the first life forms appeared.

Banded Iron Formations (BIFs)

Layers of iron-rich rocks that show evidence of early oxygen production by ancient bacteria.

Accretion

Process of particles colliding and sticking together to form larger bodies like planetesimals and planets.

Big Bang Theory

Leading explanation of universe formation caused by a cataclysmic explosion; ~13.8 Ga

Biochemical Theory

Chemical evolution from simple organic compounds (inorganic model); “Primordial Soup”; currently accepted.

Cyanobacteria

Ancient bacteria that can perform photosynthesis and were some of the first life forms to produce oxygen.

Differentiation

The process where a planet separates into different layers, like a core, mantle, and crust, based on density.

Fusion

A nuclear reaction where small atoms combine to form a larger atom, releasing a lot of energy, like in the sun or nebula.

Giant Impact Hypothesis

Moon formed from debris after a colossal collision with a Mars-sized body; tilted Earth's axis.

Hadean Eon

The earliest time period in Earth's history, about 4.6 to 4 billion years ago, when the planet was forming and cooling down; no rock record.

Hydrothermal vents

Openings on the ocean floor that release hot, mineral-rich water, and can support unique life forms.

Magnetosphere

The region around a planet dominated by its magnetic field, protecting it from solar wind; produced because of the movement of molten iron in the outer core and the solar wind.

Nebula

Slowly rotating and collapsing cloud of dust and light gases; where stars and planets can form.

Nebular Theory

The idea that the solar system formed from a large cloud of gas and dust which collapsed under gravity to form the Sun and planets.

Outgassing

The release of gases from inside a planet to its surface, contributing to the atmosphere; contains material like water and carbon dioxide.

Photochemical dissociation

Process that generates oxygen; the breakup of H₂O molecules into H and O.

Photosynthesis

Process that generates oxygen; the splitting of carbon dioxide into carbon and free oxygen

Precambrian

The time period in Earth's history before complex life appeared, covering the Hadean, Archean, and Proterozoic eons.

Spontaneous generation

The outdated idea that living organisms could arise from nonliving/inorganic (abiogenesis) matter on their own.

Stromatolites

Layered sedimentary structures created by the growth of cyanobacteria (photosynthetic microorganisms) in shallow water; often found in fossil form.

Detrital zircons

From the Hadean Eon; provide the oldest evidence of Earth's crust, revealing insights into the early formation and conditions of the planet.

Early Atmospheres

Primarily hydrogen, helium, and volcanic gases like water vapor, carbon dioxide, nitrogen, and methane.

Formation of Early Atmospheres

Gases from the nebula and volcanic eruptions contributed to the formation of early atmospheres.

Theories on Life Formation

Biochemical Theory (Primordial Soup), Hydrothermal Vent Theory, Panspermia Theory.

Evidence of Life

Fossils, stromatolites, hyperthermophiles, Banded Iron Formations (BIFs).

Beginning of Life

Earliest evidence at 3.7-3.8 Ga; verifiable evidence at 3.5 Ga (fossil bacteria).

Hadean Eon Events

Earth accretion, meteorite bombardment, detrital zircons, crust formation, Acasta Gneiss.

Archean Eon Events

Formation of secondary atmosphere, earliest life evidence, plate tectonics start, cyanobacterial mats, BIFs.