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Patrice F. Rey - One of the best experts on this subject based on the ideXlab platform.

  • The evolution of the Sr-87/Sr-86 of marine carbonates does not constrain Continental growth
    Precambrian Research, 2013
    Co-Authors: Nicolas Flament, Nicolas Coltice, Patrice F. Rey
    Abstract:

    Many Continental growth models have been proposed over the years to explain geological and geochemical data. Amongst these data, the evolution of the Sr-87/Sr-86 of marine carbonates has been used as an argument in favour of delayed Continental growth models and of a Neoarchean pulse in Continental growth. This interpretation requires that Continental Freeboard and Continental hypsometry have remained constant throughout Earth's history. However, recent studies suggest that Archean sea levels were higher, and Archean relief lower, than present-day ones. To assess the validity of the evolution of the Sr-87/Sr-86 of marine carbonates as a proxy for Continental growth, we have developed a model that evaluates the co-evolution of mantle temperature, Continental hypsometry, sea level, ridge depth, emerged area of Continental crust and the Sr-87/Sr-86 of ocean water as a function of Continental growth. We show that Archean sea levels were between similar to 500 m and similar to 1800 m higher than present-day ones, that Archean mid-oceanic ridges were between similar to 700 m and similar to 1900 m shallower than present-day ones, and that the Archean emerged land area was less than similar to 4% of Earth's area. Importantly, the evolution of the area of emerged land, contrary to that of sea level and ridge depth, barely depends on Continental growth models. This suggests that the evolution of surface geochemical proxies for felsic lithologies does not constrain Continental growth. In particular, the evolution of the Sr-87/Sr-86 of ocean water predicted for an early Continental growth model is in broad agreement with the Sr-87/Sr-86 data on marine carbonates when changes in Continental Freeboard and Continental hypsometry are taken into account. We propose that the Neoarchean shift in the Sr-87/Sr-86 of marine carbonates recorded the emergence of the continents rather than a pulse in Continental growth. Since the evolution of other geochemical indicators for felsic crust used as proxies for Continental growth is equally well explained by Continental emergence, we suggest that there could be no need for delayed Continental growth models.

Patrick George Eriksson - One of the best experts on this subject based on the ideXlab platform.

  • precambrian Continental Freeboard and geological evolution a time perspective
    Earth-Science Reviews, 2006
    Co-Authors: Patrick George Eriksson, Rajat Mazumder, Octavian Catuneanu, A J Bumby, Ountsche B Ilondo
    Abstract:

    Abstract Continental crustal growth rates, crustal volumes/thicknesses, and Continental Freeboard are considered to be intimately related; however none are easy to quantify, least of all in the Precambrian. Additionally, crustal volumes/thicknesses and isostasy are related to changing mantle heat and the concomitant variation in thickness of ocean crust. Another set of variables would be the interaction of plate tectonics (and the onset of plate tectonics, a contentious issue in itself) and mantle plumes/superplumes. Further complication is provided by the ranges of Freeboard elevations and eustatic sea level changes overlapping in scale, and sharing common genetic causes. The “constant Freeboard model” suggests that the net results of the interaction of this complex set of variables has been that Continental elevation relative to sea level, has remained essentially similar, on a global average basis, over much of geological time, assuming an essentially constant ocean volume since c. 3.8 Ga. Application of this model to the Precambrian geological record suggests that sigmoidal crustal growth rate models are probably the most reliable. A conundrum of the constant Freeboard model would be that Freeboard would tend to become lowered towards mean sea level for any specific craton over time; this “Freeboard-equilibrium” would be interrupted for a particular craton by active geodynamic processes resulting from the interplay of plate tectonics and mantle thermal instabilities. In this paper we test the validity of this thesis of alternating approximate Freeboard-equilibrium and active geodynamics, by examining the volcano-sedimentary record of a number of cratons: Kaapvaal, Singhbhum and Pilbara. For the Singhbhum craton (and bearing in mind its poor chronological data base), Freeboard-equilibrium appears to have prevailed until c. 2.1 Ga, but for Kaapvaal and Pilbara, until c. 1.8 Ga, the geodynamic processes largely outweighed the tendency towards equilibrium, except for c. 200 My from c. 2.6 to 2.4 Ga when global sea level appears to have remained high and transgression was the norm. We thus tentatively add the plate tectonic cycle and mantle-thermal processes to the already complex association of concepts controlling Continental Freeboard over time.

  • Sea level changes and the Continental Freeboard concept: general principles and application to the Precambrian
    Precambrian Research, 1999
    Co-Authors: Patrick George Eriksson
    Abstract:

    Abstract Eustatic sea level changes reflect variation in ocean water or ocean basin volume, or changes to the hypsometric curve, which is in itself geographically and chronologically variable. Freeboard, the elevation of a continent above mean sea level, is closely related to changes in both sea level and this curve. Relative sea level change occurs due to tectonism, sediment supply, compaction, and eustatic movements. Hydroisostatic compensation modifies first-order sea level variation by about one-third. Short term and localised change in sea level may be ascribed to waves and tides, storm winds, hurricanes, tsunamis and catastrophic sediment slumps. Wide, gently sloping shelves with more uniform circulation systems, inferred for the Precambrian, may have enhanced tide and wave-induced sea level changes. Salinity and water temperature, mutually dependent, affect eustatic and relative sea levels; elevated water temperatures postulated for the early Precambrian would have been offset partly by enhanced evaporation and increased salinity. Longer term changes in sea level, regional or eustatic, may result from orogenesis, volcanism, sediment supply, compaction and loading, isostasy, and thermal mechanisms. Glacioeustatic changes, compounded by related salinity variations, moderated by glacioisostatic effects and modified by hydroisostasy, reach ca 150 m. Isostatic rebound in interglacial episodes will produce rapid and marked sea level drops up to ca 250 m; this is a localised effect and contrasts with the global enhancement of sea level during interglacials. However, evidence for glaciation in the geological record is limited, also for most of the Precambrian; sea level oscillations in non-glacial episodes may reflect flexure of tectonic plates (change up to ∼100 m) or changes to Earth's geoid (∼250 m). Eustasy up to ∼350 m will result from change to ocean basin volume, due to variation in mid-ocean ridge volume and spreading rates, also related to supercontinent amalgamation and breakup. Intra-plate hot spots and oceanic plateaus will change eustatic sea level more slowly, up to ∼100 m. Higher heat flow in the Archaean and concomitant enhanced volcanism suggest that these were important influences on Precambrian sea levels. The exponential elevation-age relationship observed for Phanerozoic oceanic lithosphere may have been more significant in the Precambrian. As Continental crust grew from ca 4.0 Ga, declining heat flow and concomitant deepening of the ocean basins maintained an approximately constant Freeboard during the Archaean. Although still hotly debated, there is strong support for episodic growth models inferring rapid formation of Continental crust near the Archaean–Proterozoic boundary. This would imply constant Freeboard conditions after 2.5 Ga as well. The constant Freeboard model, however, is one based on average global conditions. Freeboard was still subject to geographic and chronologic variation, and these potential changes lie within the bounds of eustatic and relative sea level change. Continental crustal growth, the Freeboard concept and sea level changes are thus interdependent variables in Precambrian geology.

  • the 2 7 2 0 ga volcano sedimentary record of africa india and australia evidence for global and local changes in sea level and Continental Freeboard
    Precambrian Research, 1999
    Co-Authors: Patrick George Eriksson, Rajat Mazumder, Subir Sarkar, Pradip K Bose, Wladyslaw Altermann, R Van Der Merwe
    Abstract:

    Abstract The 2.7–2.0 Ga volcano-sedimentary records of the African, Indian and Australian cratons indicate two broadly defined periods of extensive drowning of the emergent Continental areas, concomitant with lowered Freeboard. Carbonate-banded iron formation (BIF) platforms characterised the first such event, at ca 2.6–2.4 Ga (Africa and Australia) to 2.7 Ga (India). These earlier globally enhanced sea levels are ascribed to increased mid-ocean ridge activity, possibly related to breakup of a postulated Late Archaean ‘southern’ supercontinent. Alternatively, a transition from global-scale catastrophic mantle overturn events to the onset of plate tectonics may have occurred in the Late Archaean (Nelson, 1998. Earth Planet. Sci. Lett. 158, 109–119). Both explanations of increased mid-ocean ridge activity are compatible with significant Early to Middle Archaean crustal growth (Armstrong, 1981. Phil. Trans. R Soc. London A 301, 443–472), with the emergent high Freeboard cratons being subjected to aggressive weathering and erosion. Enhanced Continental crustal growth near the Archaean–Proterozoic boundary (McLennan and Taylor, 1982. J. Geol. 90, 347–361), related to the development of significant island arc complexes, would have resulted in common lowered Freeboard–enhanced sea level conditions at the passive margins of the ‘southern’ cratons. The diachronous nature of these earlier transgressions in the various cratons may reflect the effect of local tectonic movements and/or the thermal state of the cratons. From ca 2.4–2.2 Ga, cratons that make up the present-day continents of India, Africa and Australia had relatively high Continental Freeboard and lowered sea levels. Glacigenic deposits are preserved on the Kaapvaal (Africa), Singhbhum (India) and Pilbara (Australia) cratons. The second broadly defined drowning event, at ca 2.15 Ga, was probably due to post-glacial climatic amelioration. Freeboard was reduced by the combination of eustatic rise and the reestablishment of aggressive weathering as warmer palaeoclimates returned. In India, carbonates were more prominent than the siliciclastic sediments (including prominent black shales) seen in Africa and Australia.

Nicolas Flament - One of the best experts on this subject based on the ideXlab platform.

  • The evolution of the Sr-87/Sr-86 of marine carbonates does not constrain Continental growth
    Precambrian Research, 2013
    Co-Authors: Nicolas Flament, Nicolas Coltice, Patrice F. Rey
    Abstract:

    Many Continental growth models have been proposed over the years to explain geological and geochemical data. Amongst these data, the evolution of the Sr-87/Sr-86 of marine carbonates has been used as an argument in favour of delayed Continental growth models and of a Neoarchean pulse in Continental growth. This interpretation requires that Continental Freeboard and Continental hypsometry have remained constant throughout Earth's history. However, recent studies suggest that Archean sea levels were higher, and Archean relief lower, than present-day ones. To assess the validity of the evolution of the Sr-87/Sr-86 of marine carbonates as a proxy for Continental growth, we have developed a model that evaluates the co-evolution of mantle temperature, Continental hypsometry, sea level, ridge depth, emerged area of Continental crust and the Sr-87/Sr-86 of ocean water as a function of Continental growth. We show that Archean sea levels were between similar to 500 m and similar to 1800 m higher than present-day ones, that Archean mid-oceanic ridges were between similar to 700 m and similar to 1900 m shallower than present-day ones, and that the Archean emerged land area was less than similar to 4% of Earth's area. Importantly, the evolution of the area of emerged land, contrary to that of sea level and ridge depth, barely depends on Continental growth models. This suggests that the evolution of surface geochemical proxies for felsic lithologies does not constrain Continental growth. In particular, the evolution of the Sr-87/Sr-86 of ocean water predicted for an early Continental growth model is in broad agreement with the Sr-87/Sr-86 data on marine carbonates when changes in Continental Freeboard and Continental hypsometry are taken into account. We propose that the Neoarchean shift in the Sr-87/Sr-86 of marine carbonates recorded the emergence of the continents rather than a pulse in Continental growth. Since the evolution of other geochemical indicators for felsic crust used as proxies for Continental growth is equally well explained by Continental emergence, we suggest that there could be no need for delayed Continental growth models.

Pons Marie-laure - One of the best experts on this subject based on the ideXlab platform.

  • The Archean Earth as constrained by stable isotopes of transition metal (Zn, Fe)
    2011
    Co-Authors: Pons Marie-laure
    Abstract:

    L’Archéen, de 4 à 2,5 Ga, est la période qui a connu les plus grands bouleversements géologiques et biologiques de l’histoire de la Terre : formation des continents, transition d’une tectonique à composante verticale vers une tectonique des plaques horizontale, apparition de la vie, … Le but de cette thèse est d’étudier les conditions environnementales de la Terre à l’Archéen, par l’analyse des compositions isotopiques de métaux de transition (Fe, Zn) de roches provenant principalement de la province d’Isua au Groenland (3,8 Ga). Après avoir adapté le protocole de séparation du Fe, Cu, Zn à des échantillons riches en Fe, nous avons acquis les données par spectrométrie de masse à source plasma et à multicollection MC-ICPMS. Nous nous sommes d’abord intéressés au processus de serpentinisation de la croûte océanique, réaction produisant à la fois des nutriments pour la vie (CH 4 , H 2 ) et des minéraux catalyseurs (mackinawite) de la formation abiotique d’acides aminés, molécules du vivant. L’affleurement d’Isua comporte une unité ophiolitique présentant les serpentinites les plus anciennes (3.81-3.70 Ga) : leur analyse permet d’appréhender la réaction de serpentinisation à l’Archéen. Les résultats obtenus pour la composition isotopique du zinc dans ces roches et dans des serpentinites modernes ont permis d’établir une correspondance entre le processus de serpentinisation à Isua et la mise en place de volcans de boues de serpentinites à l’aplomb de la fosse des Mariannes. Nous avons ainsi pu identifier Isua comme une zone d’arrière-arc de subduction océanique, lieu d’une serpentinisation produisant des fluides de température variable (100-300°C) et de pH alcalin (9-12). Nous montrons que cette configuration atypique réunissant serpentinisation, fluides alcalins et édifices volcaniques est favorable à l’émergence du vivant. Nous avons ensuite analysé de nombreux échantillons de formations de fer rubané (BIFs), sédiments propres à l’Archéen et au début du Protérozoïque. L’évolution de la composition isotopique du zinc de ces échantillons au cours du temps a permis d’établir une chronologie de l'émersion des continents.Nos résultats sont en faveur d’une émersion débutant il y a 2,9 Ga. Enfin, nos données nous informent sur la colonisation des continents émergés par la vie à 2,6 Ga et sur la pédogenèse de sols archéens comportant un horizon organique.During the Archean (4 to 2.5 Ga ago), the Earth experienced the biggest changes in terms of geological and biological settings – Continental growth, transition from sagduction towards purely horizontal plate tectonics, emergence of life, … The purpose of the present study is to better understand the archean earth environment by measuring the isotopic composition of transition metals – Zn, Fe – of archean rocks. Most of the samples belong to the Isua supracrustal belt, in Greenland, dated 3.8 Ga. The chemical extraction protocol of Fe, Cu, Zn was adapted to our Fe-rich samples and isotopic analyses were conducted by multicollection inductively coupled plasma mass spectrometry. The serpentinization of the oceanic crust produces fuels for life (CH 4 , H 2 ) and mackinawite, which catalyses formation of complex organic compounds. Serpentinization may thus provide a suitable environment for the emergence of the first biomolecules. We analysed the oldest known serpentinites from Isua (3.81-3.70 Ga) to comprehend the archean serpentinization process. The isotopic compositions of zinc reported in this samples and in modern serpentinites attest to a strong similarity between Isua and the Mariana serpentinite mud volcanoes. We identified Isua as an oceanic forearc environment permeated by high-pH (9-12) hydrothermal solutions at medium temperature (100-300°C). We show that such an environment could have fostered the emergence of early life. We also analyzed several banded iron formations (BIF), which are sediments limited to the Archean and Proterozoic. The temporal evolution of these samples' isotopic composition shows a close relationship with the Continental Freeboard. Our results support the Continental emersion starting 2.9 Ga ago. Besides, we identified the life colonization of continents at 2.6 Ga together with pedogenesis of archean soils with an organic horizon

  • La Terre à l'Archéen. Apport des isotopes de métaux de transition (Zn, Fe)
    HAL CCSD, 2011
    Co-Authors: Pons Marie-laure
    Abstract:

    During the Archean (4 to 2.5 Ga ago), the Earth experienced the biggest changes in terms of geological and biological settings – Continental growth, transition from sagduction towards purely horizontal plate tectonics, emergence of life, … The purpose of the present study is to better understand the archean earth environment by measuring the isotopic composition of transition metals – Zn, Fe – of archean rocks. Most of the samples belong to the Isua supracrustal belt, in Greenland, dated 3.8 Ga. The chemical extraction protocol of Fe, Cu, Zn was adapted to our Fe-rich samples and isotopic analyses were conducted by multicollection inductively coupled plasma mass spectrometry. The serpentinization of the oceanic crust produces fuels for life (CH 4 , H 2 ) and mackinawite, which catalyses formation of complex organic compounds. Serpentinization may thus provide a suitable environment for the emergence of the first biomolecules. We analysed the oldest known serpentinites from Isua (3.81-3.70 Ga) to comprehend the archean serpentinization process. The isotopic compositions of zinc reported in this samples and in modern serpentinites attest to a strong similarity between Isua and the Mariana serpentinite mud volcanoes. We identified Isua as an oceanic forearc environment permeated by high-pH (9-12) hydrothermal solutions at medium temperature (100-300°C). We show that such an environment could have fostered the emergence of early life. We also analyzed several banded iron formations (BIF), which are sediments limited to the Archean and Proterozoic. The temporal evolution of these samples' isotopic composition shows a close relationship with the Continental Freeboard. Our results support the Continental emersion starting 2.9 Ga ago. Besides, we identified the life colonization of continents at 2.6 Ga together with pedogenesis of archean soils with an organic horizon.L’Archéen, de 4 à 2,5 Ga, est la période qui a connu les plus grands bouleversements géologiques et biologiques de l’histoire de la Terre : formation des continents, transition d’une tectonique à composante verticale vers une tectonique des plaques horizontale, apparition de la vie, … Le but de cette thèse est d’étudier les conditions environnementales de la Terre à l’Archéen, par l’analyse des compositions isotopiques de métaux de transition (Fe, Zn) de roches provenant principalement de la province d’Isua au Groenland (3,8 Ga). Après avoir adapté le protocole de séparation du Fe, Cu, Zn à des échantillons riches en Fe, nous avons acquis les données par spectrométrie de masse à source plasma et à multicollection MC-ICPMS. Nous nous sommes d’abord intéressés au processus de serpentinisation de la croûte océanique, réaction produisant à la fois des nutriments pour la vie (CH 4 , H 2 ) et des minéraux catalyseurs (mackinawite) de la formation abiotique d’acides aminés, molécules du vivant. L’affleurement d’Isua comporte une unité ophiolitique présentant les serpentinites les plus anciennes (3.81-3.70 Ga) : leur analyse permet d’appréhender la réaction de serpentinisation à l’Archéen. Les résultats obtenus pour la composition isotopique du zinc dans ces roches et dans des serpentinites modernes ont permis d’établir une correspondance entre le processus de serpentinisation à Isua et la mise en place de volcans de boues de serpentinites à l’aplomb de la fosse des Mariannes. Nous avons ainsi pu identifier Isua comme une zone d’arrière-arc de subduction océanique, lieu d’une serpentinisation produisant des fluides de température variable (100-300°C) et de pH alcalin (9-12). Nous montrons que cette configuration atypique réunissant serpentinisation, fluides alcalins et édifices volcaniques est favorable à l’émergence du vivant. Nous avons ensuite analysé de nombreux échantillons de formations de fer rubané (BIFs), sédiments propres à l’Archéen et au début du Protérozoïque. L’évolution de la composition isotopique du zinc de ces échantillons au cours du temps a permis d’établir une chronologie de l'émersion des continents.Nos résultats sont en faveur d’une émersion débutant il y a 2,9 Ga. Enfin, nos données nous informent sur la colonisation des continents émergés par la vie à 2,6 Ga et sur la pédogenèse de sols archéens comportant un horizon organique

  • La Terre à l'Archéen. Apport des isotopes de métaux de transition (Zn, Fe)
    2011
    Co-Authors: Pons Marie-laure, Albarede Francis
    Abstract:

    L Archéen, de 4 à 2,5 Ga, est la période qui a connu les plus grands bouleversements géologiques et biologiques de l histoire de la Terre : formation des continents, transition d une tectonique à composante verticale vers une tectonique des plaques horizontale, apparition de la vie, Le but de cette thèse est d étudier les conditions environnementales de la Terre à l Archéen, par l analyse des compositions isotopiques de métaux de transition (Fe, Zn) de roches provenant principalement de la province d Isua au Groenland (3,8 Ga). Apre s avoir adapté le protocole de séparation du Fe, Cu, Zn à des échantillons riches en Fe, nous avons acquis les données par spectrométrie de masse à source plasma et à multicollection MC-ICPMS. Nous nous sommes d abord intéressés au processus de serpentinisation de la croûte océanique, réaction produisant à la fois des nutriments pour la vie (CH 4 , H 2 ) et des minéraux catalyseurs (mackinawite) de la formation abiotique d acides aminés, molécules du vivant. L affleurement d Isua comporte une unité ophiolitique présentant les serpentinites les plus anciennes (3.81-3.70 Ga) : leur analyse permet d appréhender la réaction de serpentinisation à l Archéen. Les résultats obtenus pour la composition isotopique du zinc dans ces roches et dans des serpentinites modernes ont permis d établir une correspondance entre le processus de serpentinisation à Isua et la mise en place de volcans de boues de serpentinites à l aplomb de la fosse des Mariannes. Nous avons ainsi pu identifier Isua comme une zone d arrière-arc de subduction océanique, lieu d une serpentinisation produisant des fluides de température variable (100-300C) et de pH alcalin (9-12). Nous montrons que cette configuration atypique réunissant serpentinisation, fluides alcalins et édifices volcaniques est favorable à l émergence du vivant. Nous avons ensuite analysé de nombreux échantillons de formations de fer rubané (BIFs), sédiments propres à l Archéen et au début du Protérozoïque. L évolution de la composition isotopique du zinc de ces échantillons au cours du temps a permis d établir une chronologie de l'émersion des continents.Nos résultats sont en faveur d une émersion débutant il y a 2,9 Ga. Enfin, nos données nous informent sur la colonisation des continents émergés par la vie à 2,6 Ga et sur la pédogenèse de sols archéens comportant un horizon organique.During the Archean (4 to 2.5 Ga ago), the Earth experienced the biggest changes in terms of geological and biological settings Continental growth, transition from sagduction towards purely horizontal plate tectonics, emergence of life, The purpose of the present study is to better understand the archean earth environment by measuring the isotopic composition of transition metals Zn, Fe of archean rocks. Most of the samples belong to the Isua supracrustal belt, in Greenland, dated 3.8 Ga. The chemical extraction protocol of Fe, Cu, Zn was adapted to our Fe-rich samples and isotopic analyses were conducted by multicollection inductively coupled plasma mass spectrometry. The serpentinization of the oceanic crust produces fuels for life (CH 4 , H 2 ) and mackinawite, which catalyses formation of complex organic compounds. Serpentinization may thus provide a suitable environment for the emergence of the first biomolecules. We analysed the oldest known serpentinites from Isua (3.81-3.70 Ga) to comprehend the archean serpentinization process. The isotopic compositions of zinc reported in this samples and in modern serpentinites attest to a strong similarity between Isua and the Mariana serpentinite mud volcanoes. We identified Isua as an oceanic forearc environment permeated by high-pH (9-12) hydrothermal solutions at medium temperature (100-300C). We show that such an environment could have fostered the emergence of early life. We also analyzed several banded iron formations (BIF), which are sediments limited to the Archean and Proterozoic. The temporal evolution of these samples' isotopic composition shows a close relationship with the Continental Freeboard. Our results support the Continental emersion starting 2.9 Ga ago. Besides, we identified the life colonization of continents at 2.6 Ga together with pedogenesis of archean soils with an organic horizon.LYON-ENS Sciences (693872304) / SudocSudocFranceF

Nicolas Coltice - One of the best experts on this subject based on the ideXlab platform.

  • The evolution of the Sr-87/Sr-86 of marine carbonates does not constrain Continental growth
    Precambrian Research, 2013
    Co-Authors: Nicolas Flament, Nicolas Coltice, Patrice F. Rey
    Abstract:

    Many Continental growth models have been proposed over the years to explain geological and geochemical data. Amongst these data, the evolution of the Sr-87/Sr-86 of marine carbonates has been used as an argument in favour of delayed Continental growth models and of a Neoarchean pulse in Continental growth. This interpretation requires that Continental Freeboard and Continental hypsometry have remained constant throughout Earth's history. However, recent studies suggest that Archean sea levels were higher, and Archean relief lower, than present-day ones. To assess the validity of the evolution of the Sr-87/Sr-86 of marine carbonates as a proxy for Continental growth, we have developed a model that evaluates the co-evolution of mantle temperature, Continental hypsometry, sea level, ridge depth, emerged area of Continental crust and the Sr-87/Sr-86 of ocean water as a function of Continental growth. We show that Archean sea levels were between similar to 500 m and similar to 1800 m higher than present-day ones, that Archean mid-oceanic ridges were between similar to 700 m and similar to 1900 m shallower than present-day ones, and that the Archean emerged land area was less than similar to 4% of Earth's area. Importantly, the evolution of the area of emerged land, contrary to that of sea level and ridge depth, barely depends on Continental growth models. This suggests that the evolution of surface geochemical proxies for felsic lithologies does not constrain Continental growth. In particular, the evolution of the Sr-87/Sr-86 of ocean water predicted for an early Continental growth model is in broad agreement with the Sr-87/Sr-86 data on marine carbonates when changes in Continental Freeboard and Continental hypsometry are taken into account. We propose that the Neoarchean shift in the Sr-87/Sr-86 of marine carbonates recorded the emergence of the continents rather than a pulse in Continental growth. Since the evolution of other geochemical indicators for felsic crust used as proxies for Continental growth is equally well explained by Continental emergence, we suggest that there could be no need for delayed Continental growth models.