The Hadean & Archean “It’s the Earth Jim, but not as we know it.”

Hadean & Archean: Myrs

Archean Divided into:

Hadean/Archean “Evidence” Problems Very few rocks/minerals exist from this period Most have been metamorphosed, or buried No fossils exist in Hadean, Minimal in Archean Rely on: Few rocks that we have Moon, Meteorites & other planets Models 4.4 Gyr Zircon Crystal

Rocks Older than 2.5 Gyrs

The Neighborhood: “Dim” Sun

The Neighborhood: “Near” Moon = Shorter Day hrs

Origin of the Moon: 4.5 Gyrs

Lunar Hypothesis 1.Capture: Formed somewhere else and was captured 2.Twin Planet: Formed from material left over from the Earth 3.Fission: “Budded” off the Earth Problem: It has the same Oxygen Chemistry as the Earth indicating it formed in the same part of the Solar System

Lunar Hypothesis 1.Capture: Formed somewhere else and was captured 2.Twin Planet: Formed from material left over from the Earth 3.Fission: “Budded” off the Earth Problem: Moon has much less iron than the Earth and is no volatiles (water & gases)

Lunar Hypothesis 1.Capture: Formed somewhere else and was captured 2.Twin Planet: Formed from material left over from the Earth 3.Fission: “Budded” off the Earth Problem: Earth was not spinning fast enough for this to be realistic.

Lunar Hypothesis 1.Capture: Formed somewhere else and was captured 2.Twin Planet: Formed from material left over from the Earth 3.Fission: “Budded” off the Earth 4.Collision: Formed when a Mars-sized body collided with the Earth Explains (1) isotopes, (2) lack of iron and volatiles, and (3) consistent with Earth’s spin rate.

Animation Link

Fred Sulahria Hadean Earth

Hadean: What We Do Know… Earth was a very different place! Major features of the Earth developed: atmosphere (throughout Hadean) oceans (water by 4.4 Gyr, stable oceans by 3.8 Gyr) crust and continents (by Gyr) plate tectonics starts (about 4.0 Gyr) magnetic field (about 4.5 Gyr) life? (no evidence yet…)

Early Earth Driven by Heat From: 1.Accretion 2.Differentiation 3.Radioactive Decay

Heat Escapes by: Resulting in Convection of Interior and Volcanism 1.Convection 2.Conduction 3.Radiation

Hadean Surface Dominated By: Meteorite Bombardment Volcanism

Heavy Bombardment Period

Heavy Bombardment on the Moon

Bombardment may have led to a Temporary “Magma Ocean”

Magma Solidified into Early Crust Komatiites Ultramafic, Dense, Uniform

Atmosphere

Atmospheric Formation Hypothesis: Captured from Solar Nebula Mostly Hydrogen and Helium Would have been quickly lost If initially lost - where did the present atmosphere come from? 1.Accreted as hydrous minerals and outgassed from volcanoes 2.Returned to Earth from comets

Secondary Atmosphere - Outgassing Initially Composed of: Ammonia (NH 3 ) Hydrogen (H 2 ) Carbon dioxide (CO 2 ) Methane (CH 4 ) Water vapor (H 2 O) Nitrogen (N 2 )

Similar to Saturn’s moon: Titan

One Reconstruction (Others have much more Carbon Dioxide in Hadean)

Note: No Significant Oxygen! Evidence: No Rust Minerals Pyrite and Uraninite Conglomerates (normally oxidize) Extensive carbon-rich rocks Witwatersrand conglomerate, South Africa (Middle Archean)

Atmospheric Evolution Primary - Captured from Solar Nebula - Mostly Hydrogen and Helium - Quickly Lost Secondary - Formed by Outgassing by Volcanoes Tertiary - Modified by Life (addition of Oxygen)

Oceans

“Raining” of the Oceans

“Vaporization” of the Oceans

Hadean Oceans Characteristics Liquid Water existed at 4.4 Gyrs “Ephemeral” (periodically vaporized) Acidic (water + carbon dioxide = carbonic acid) Probably “salty” Stabilized by end of Hadean (about 3.8 Gyrs) Evidence Jack Hills Formation zircon crystals with water inclusions solar system evidence for heavy bombardment and models no limestones, atmospheric models acidic water (dissolves ions) first limestones & sedimentary rocks

One Reconstruction (Other hypothesize much less water from comets)

Return to the Crust

Continents Formation Requires Plate Tectonics