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Hadean &
Archean: 2500-4600 Myrs
Era Age (Myrs) Epoch
0.01Holocene
1.8Pleistocene
5.3Pliocene
23.8Miocene
33.6Oligocene
54.8Eocene
65Paleocene
144
206
248
290
323
354
417
443
490
543
2500
3800
Precambrian
Phanerozoic
Eon
Proterozoic
Archean
Hadean
Period
Quaternary
Tertiary
Neogene
Paleocene
Mississippian
Cenozoic
Mesozoic
Paleozoic
Cretaceous
Jurassic
Age of the Earth 4600 Myrs (4.6 Byrs)Source: Geological Society of America (1999)
Geologic Time Scale
Devonian
Silurian
Ordivician
Cambrian
Triassic
Permian
Pennsylvanian
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
Lunar Hypothesis1. 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 Hypothesis1. 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 Hypothesis1. Capture: Formed
somewhere else and was captured
2. Twin Planet: Formed from material left over from the Earth
3. Fission: “Budded”off the Earth
QuickTime™ and aMicrosoft Video 1 decompressorare needed to see this picture.
Problem: Earth was not spinning fast enough for this to be realistic.
Lunar Hypothesis1. 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
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 4.4-4.0 Gyr)• plate tectonics starts (about 4.0 Gyr)• magnetic field (about 4.5 Gyr)• life? (no evidence yet…)
Heat Escapes by:
Resulting in Convection of Interior and Volcanism
1. Convection2. Conduction3. Radiation
Atmospheric FormationHypothesis: 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 volcanoes2. Returned to Earth from comets
Secondary Atmosphere - Outgassing
Initially Composed of:• Ammonia (NH3)• Hydrogen (H2)• Carbon dioxide (CO2)• Methane (CH4)• Water vapor (H2O)• Nitrogen (N2)
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 EvolutionPrimary - Captured from Solar Nebula
- Mostly Hydrogen and Helium- Quickly Lost
Secondary - Formed by Outgassing by Volcanoes
Tertiary - Modified by Life (addition of Oxygen)
Hadean OceansCharacteristics• 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