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Hadeon Eon

hadeon.htm

A collection from Wikipedia: - https://en.wikipedia.org/wiki/Hadean 180306, 180423
and other websites.

Downloaded and edited by U Kyaw Tun (UKT) (M.S., I.P.S.T., USA), and staff of Tun Institute of Learning (TIL) . Not for sale. No copyright. Free for everyone. Prepared for students and staff of TIL Research Station, Yangon, MYANMAR 
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Contents of this page

Introduction
1.0. Etymology
2.0. Subdivisions
3.0. Hadean rocks
4.0. Atmosphere and oceans

 

The following to be checked and copied
if relevant:
5 See also
6 References
7 Further reading
8 External links

 

UKT notes
 

 

Contents of this page

Introduction

- UKT 180306: Hadeon Eon is the first Eon of the Precambrian Supereon. We can imagine it to be the first cooling of the molten globe. No land mass and therefore no rocks as we know could be there. It would simply be like Hell or Hades as the Greek would say. It is from this Greek word that the name for this Eon is derived.

From: - https://en.wikipedia.org/wiki/Hadean 180306

The Hadean Eon is a geologic eon of the Earth predating the Archean Eon. It began with the formation of the Earth about 4.6 Ga ago (billion years ago) and ended, as defined by the ICS (International Commission on Stratigraphy), 4 Ga ago (billion years ago). [1] As of 2016 [update], the ICS describes its status as informal. [2] The geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth. W. Brian Harland later coined an almost synonymous term: the "Priscoan period". Other, older texts simply refer to the eon as the Pre-Archean.

From: https://www.britannica.com/science/Hadean-Eon 180306

Hadean Eon, informal division of Precambrian time occurring between about 4.6 Ga and about 4.0 Ga ago (billion years ago). The Hadean Eon is characterized by Earth’s initial formation -- from the accretion of dust and gases and the frequent collisions of larger planetesimals -- and by the stabilization of its core and crust and the development of its atmosphere and oceans. Throughout part of the eon, impacts from extraterrestrial bodies released enormous amounts of heat that likely prevented much of the rock from solidifying at the surface. As such, the name of the interval is a reference to Hades, a Greek translation of the Hebrew word for hell.

Earth’s surface was incredibly unstable during the early part of the Hadean Eon. Convection currents in the mantle brought molten rock to the surface and caused cooling rock to descend into magmatic seas. [UKT ¶]

UKT 180306: Don't think Magma to be uniform. Since the Earth contains not only some 92 common elements and about 20 radioactive elements, and since almost all elements have isotopes of different atomic masses (for example iron 26Fe has 4 stable isotopes 26Fe56, 26Fe54, 26Fe57, and 26Fe58), slowing cooling magma that has come up to the surface, would be full of blobs of slightly different densities, and the whole mass would be like porridge cooling down. Refer to Isotopic Mass and Natural Abundance in TIL HD-PDF and SD-PDF libraries:
- AAudiEtAl-IsotopicMassNatAbund<Ô> / Bkp<Ô> (link chk 180306)

UkT 180306: The convention I use to express isotopic mass is: atomic number as subscript followed by chemical symbol, and isotopic mass number as superscript.

Heavier elements, such as iron 26Fe, descended to become the core, whereas lighter elements, such as silicon 14Si , rose and became incorporated into the growing crust. Although no one knows when the first outer crust of the planet formed, some scientists believe that the existence of a few grains of zircon (from zirconium 40Zr) dated to about 4.4 Ga confirm the presence of stable continents, liquid water, and surface temperatures that were probably less than 100 °C (212 °F). [UKT ¶]

UKT 180309: Don't be confused by the terms zircon and zirconium 40Zr. Zircon is a mineral - a silicate , zirconium silicate (ZrSiO4).

Since Hadean times, nearly all of this original crust has subducted from the movements of tectonic plates, and thus few rocks and minerals remain from the interval. The oldest rocks known are the faux amphibolite volcanic deposits of the Nuvvuagittuq greenstone belt in Quebec, Canada; they are estimated to be 4.28 Ga old. The oldest minerals are the aforementioned grains of zircon, which were found in the Jack Hills of Australia.

UKT 180309: "Amphibolite, a rock composed largely or dominantly of minerals of the amphibole group. The term has been applied to rocks of either igneous or metamorphic origin. In igneous rocks, the term hornblendite is more common and restrictive; hornblende is the most common amphibole and is typical of such rocks. Hornblendite is an ultramafic rock (dominantly dark minerals). True hornblendites contain little other than amphibole and are probably derived from the alteration of pyroxene and olivine." https://www.britannica.com/science/amphibolite 180309

Considerable debate surrounds the timing of the formation of the atmosphere as well as its initial composition. Although many scientists contend that the atmosphere and the oceans formed during the latter part of the eon, the discovery of the zircon grains in Australia provide compelling evidence that the atmosphere and ocean formed before 4.4 Ga ago (billion years ago). The early atmosphere likely began as a region of escaping hydrogen H2 and helium He. [UKT ¶]

 UKT 180306: The Sun's energy is the result of Nuclear Fusion as opposed to Nuclear Fission. If we were to speculate that Helium 2He (monatomic inert gas) resulted from Nuclear Fusion, we must speculate that at the beginning of Hadeon Eon, the Earth must have enough Deuterium 1H2 (stable isotope) and Tritium 1H3 (radioactive isotope) to produce 2He4 .
Refer to Isotopic Mass and Natural Abundance in TIL HD-PDF and SD-PDF libraries:
-AAudiEtAl-IsotopicMassNatAbund<Ô> / Bkp<Ô> (link chk 180306)
"Percentage abundance: 1H1 99.9885 ; 1H2 0.0115 ; 1H3 * ; 2He3 0.000137; 2He4 99.999863
(*) in the abundance column indicate that it is not present in nature
or that a meaningful natural abundance cannot be given"

It is generally thought that ammonia NH3, methane CH4, and neon Ne, were present sometime after the crust cooled, and volcanic outgassing added water H2O vapour, nitrogen N2, and additional hydrogen H2. Some scientists state that ice delivered by comet impacts could have supplied the planet with additional water vapour. Later, it is thought, much of the water vapour in the atmosphere condensed to form clouds and rain that left large deposits of liquid water on Earth’s surface.

Contents of this page

1.0. Etymology

From: https://en.wikipedia.org/wiki/Hadean 180307

"Hadean" (from Hades, the Greek god of the underworld) describes the hellish conditions then prevailing on Earth: the planet had just formed and was still very hot owing to its recent accretion, the abundance of short-lived radioactive elements*, and frequent collisions with other Solar System bodies.

*UKT 180423: Short-lived radioactive elements. Long ago before my retirement from Myanmar university service, I had written a paper on this subject. It was published in a Burma Research Journal of the time when we were forbidden, to published in journals published in foreign countries, unless allowed by the Ministry of Education. My attempts to get the permission got bogged in the red-tape of various ministries. It was death for a research scientist. My wife, Daw Than Than and I had spent the best years of our lives in Myanmar university service: 34 of her's, and 33 of mine. Now, I'm reading the following Wikipedia articles with a heavy heart:
List of elements by stability of isotopes
  - https://en.wikipedia.org/wiki/List_of_elements_by_stability_of_isotopes 180423
Island of stability
  - https://en.wikipedia.org/wiki/Island_of_stability 180423

From: The Eons of Chaos and Hades, by C. Goldblatt, K. J. Zahnle, N. H. Sleep, and E. G. Nisbet , Solid Earth, 1, 1–3, 2010, www.solid-earth.net/1/1/2010/
- CGoldblattEtAl-EonsChaosHades2010<Ô> / Bkp<Ò> (link chk 180306)

Abstract. We propose the Chaotian Eon to demarcate geologic time from the origin of the Solar System to the Moon-forming impact on Earth. This separates the solar system wide processes of planet formation from the subsequent divergent evolution of the inner planets. We further propose the division of the Hadean Eon into eras and periods and naming the proto-Earth Tellus.

UKT 180307: To get a perspective of formation and evolution of planets, view videos on inner vs. outer planets:
1. Solar system 101 National Geographic - SolarSys101NatGeog<Ô> / Bkp<Ô> (link chk 180307)
2. Inner and outer planets - InnerOuterPlanets<Ô> / Bkp<Ô> (link chk 180307)
"There are eight planets that orbit our Sun, but did you know that they can be separated into two groups. One group includes four planets nearest to the Sun: Mercury, Venus, Earth, and Mars. These are known as the inner planets or the terrestial planets. ..."

1. Introduction: All Earth’s geology depends on the composition and structure of the planet. This, in turn, depends on how the Earth formed in the violent beginning of our solar system. It is part provenance (where the Earth happened to form) and part chance (the stochastics of formation) (Stevenson, 2008). To describe the early Earth, we must bring the processes of formation into the same framework as its subsequent geological evolution. To this end, we propose the Chaotian Eon for the time of planet formation. Within this eon, the relative timing of events is now well understood though not constrained in absolute times. Accordingly, we propose a relative timescale in terms of era and periods.
   The present (2009) International Commission on Stratigraphy timescale (http://www.stratigraphy.org/upload/ISChart2009.pdf) is rather sparse in its description of the earliest Earth, only noting the Hadean as an “informal” eon. Conversely, the description of this time proceeds rapidly, with increasing geochemical and theoretical study. The lack of a timescale leads to repeated and the unsatisfactory use of descriptive timing, e.g. “the time after the Moon-forming impact” and comparison of rocks and events based on imprecise radiometric dates. Subdivision of the Hadean will allow these to be described in their proper relative order.

2. The Chaotian: Planetary formation begins with the separation of solids from gas in the solar nebula and is followed by a period of hierarchic growth culminating in massive collisions between proto-planets (Chambers, 2004). For the proto-planets which became the Earth and the Moon, the last major collision was an oblique impact between a Mars-size body and the Venus-size proto-Earth, which ejected mantle material to form the Moon and left the planet molten (Canup, 2004). This cataclysm was the true birth of Earth. It separates our proposed solar system wide Chaotian Eon from the subsequent stratigraphic evolution of each inner planet.
   Naming this eon, we emphasise that composition of the inner planets and, thus, their geology results from the chaotic interaction of planetary embryos. ...

Contents of this page

2.0. Subdivisions

From: https://en.wikipedia.org/wiki/Hadean 180307

Since few geological traces of this eon remain on Earth, there is no official subdivision. However, the Lunar geologic timescale embraces several major divisions relating to the Hadean, [UKT ¶]

"The Lunar geological timescale (or Selenological timescale) divides the history of Moon (the Earth's satilite) into five generally recognized periods: the Copernican, Eratosthenian, Imbrian (Late and Early epochs), Nectarian, and Pre-Nectarian. The boundaries of this time scale are related to large impact events that have modified the lunar surface, ..."
- https://en.wikipedia.org/wiki/Lunar_geologic_timescale 180307
"In Greek mythology, Selene (Σελήνη) is the goddess of the moon. She is the daughter of the Titans Hyperion and Theia, and sister of the sun-god Helios, and Eos, goddess of the dawn." - https://en.wikipedia.org/wiki/Selene 180307
Note: Don't mix up the Greek and Roman mythologies: Luna is Roman and Selene is Greek.)

So the divisions are sometimes used in an informal sense to refer to the same periods of time on Earth.

The Lunar divisions are:

Pre-Nectarian, from the formation of the Moon's crust (4,533 Ma ago) up to about 3,920 Ma ago.

Nectarian ranging from 3,920 Ma ago up to about 3,850 Ma ago, in a time when the Late Heavy Bombardment, according to that theory, was in a stage of decline.

In 2010, an alternative scale was proposed that includes the addition of the Chaotian Eon and Prenephelean Eon preceding the Hadean, and divides the Hadean into three eras with two periods each. The Paleohadean era consists of the Hephaestean (4.5-4.4 Ga) and the Jacobian periods (4.4-4.3 Ga). The Mesohadean is divided into the Canadian (4.3-4.2 Ga) and the Procrustean periods (4.2-4.1 Ga). The Neohadean is divided into the Acastan (4.1-4.0 Ga) and the Promethean periods (4.0-3.9 Ga ). [3] As of February 2017 [update] this has not been adopted by the IUGS (International Union of Geological Sciences).

The Prechaotian Eon is a relatively recent addition to the timescale, having been proposed by Goldblatt et al. as the Prenephelean Eon in 2010 and not having been subdivided or formally termed an eon.  However, it is no longer the earliest eon on the timescale, being preceded by the Preuniversal Eon due to recent studies that suggest that an older universe collapsed, giving rise to the current one, and that multiple universes may currently exist. -- https://sites.google.com/site/geologicdatascale/prechaotian 180307

 

Contents of this page

3.0. Hadean rocks

From: https://en.wikipedia.org/wiki/Hadean 180308

In the last decades of the 20th century geologists identified a few Hadean rocks from Western Greenland, North-western Canada, and Western Australia. [UKT ¶]

UKT 180308: If you want to know how isotopic ratios have played the part of chronometers see a downloaded pdf paper on
Influence of Hadean crust evident in basalts and cherts from the Pilbara Craton, by S. G. Tessalina, B. Bourdon, M. Van Kranendonk, JL. Birck, and P. Philippot, 2010
- SGTessalinEtAl-HadeCrustBasaltChertPilbaraCraton<Ô> / Bkp<Ô> (link chk 180308)
"Application of the 62Sm14760Nd143 and 62Sm14660Nd142 chronometers has suggested that the initial differentiation of Earth’s mantle into enriched and depleted reservoirs may have begun within the first 100 - 200 Ma years of Earth’s history".

In 2015, traces of carbon minerals interpreted as "remains of biotic life" were found in 4.1-billion-year-old rocks in Western Australia. [4] [5]

UKT 180308: Biotic life or "Biotic material or biological derived material, is any material that originates from living organisms. Most such materials contain carbon and are capable of decay. The earliest life on Earth arose at least 3.5 Ga ago. [1] [2] [3] Earlier physical evidences of life include graphite, a biogenic substance, in 3.7 Ma-old metasedimentary rocks discovered in southwestern Greenland, [4] as well as, "remains of biotic life" found in 4.1 Ga-old rocks in Western Australia. [5] [6] "
- https://en.wikipedia.org/wiki/Biotic_material 180308

The oldest dated zircon crystals, enclosed in a metamorphosed sandstone conglomerate in the Jack Hills of the Narryer Gneiss Terrane of Western Australia, date to 4.404 ± 0.008 Ga. [6] This zircon is a slight outlier, with the oldest consistently-dated zircon falling closer to 4.35 Ga [6] -- around 200 million years after the hypothesized time of the Earth's formation.

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4.0. Atmosphere and oceans

From: https://en.wikipedia.org/wiki/Hadean 180308

A sizeable quantity of water H2O would have been in the material that formed the Earth. [7]

UKT 180308: Molecular H2O cannot be the liquid form above a certain temperature., most likely in the gaseous form depending on the temperature.

Molecular H2O can also breaks apart at high temperatures, e.g. "at 3000 deg C, more than half of the water molecules are decomposed". See Wkipedia:
- https://en.wikipedia.org/wiki/Water_splitting

Water molecules would have escaped Earth's gravity more easily when it was less massive during its formation. Hydrogen and helium are expected to continually escape (even to the present day) due to atmospheric escape. [UKT ¶]

Part of the ancient planet is theorized to have been disrupted by the impact that created the Moon, which should have caused melting of one or two large regions of the Earth. Earth's present composition suggests that there was not complete remelting as it is difficult to completely melt and mix huge rock masses. [8] However, a fair fraction of material should have been vaporized by this impact, creating a rock vapor atmosphere around the young planet. [UKT ¶]

The rock vapor would have condensed within two thousand years, leaving behind hot volatiles which probably resulted in a heavy CO2 atmosphere with hydrogen and water vapor. [UKT ¶]

Liquid water oceans existed despite the surface temperature of 230 °C (446 °F) because at an atmospheric pressure of above 27 atm., caused by the heavy CO2 atmosphere, water is still liquid. As cooling continued, subduction and dissolving in ocean water removed most CO2 from the atmosphere, but levels oscillated wildly as new surface and mantle cycles appeared. [9]

Studies of zircons have found that liquid water must have existed as long ago as 4.4 Ga ago, very soon after the formation of the Earth. [10]| [11] [12] This requires the presence of an atmosphere. The Cool Early Earth theory covers a range from about 4.4 - 4.0 Ga years.

UKT 180309: A paper on Cool Early Earth , by John W. Valley, William H. Peck, Elizabeth M. King, and Simon A. Wilde, 2002 is in TIL HD-PDF and SD-PDF libraries:
- JWValleyEtAl-ACoolEarlyEarth<Ô> / Bkp<Ô> (link chk 180309)
"No known rocks have survived from the first 500 Ma of Earth history, but studies of single zircons suggest that some continental crust formed as early as 4.4 Ga, 160 Ma after accretion of the Earth, and that surface temperatures were low enough for liquid water. ..."

 

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UKT notes

 

 

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