Source regions and timescales for the delivery of water to the Earth

“Morbidelli et al. (2000) suggested the Earth acquired its water by accretion of a planetary embryo with water content 1–10wt. %, like carbonaceous chondrite material.”

“The best explanation for the origin of Earth’s water is that water-rich chondritic planetary embryos formed in the outer asteroid region and were perturbed inwards during Earth’s formation (Morbidelli et al. 2000).”

“Assuming that the planet formed in situ, it will have been subjected to water delivery during the late heavy bombardment, although it has been suggested by Morbidelli et al. (2000) that terrestrial planets can accrete significant water during formation without the need for cometary impacts.”

“Moreover, Morbidelli et al. (2000)(author?)”

“Impacts by water-rich planetesimals probably delivered most of the Earth’s surface volatiles during the clearing phase (e.g. Morbidelli et al. 2000).”

“Theoretical arguments rule them out as the only source of Earth’s water because many more comets would exist in the outer parts of the solar system than is currently thought to be possible (Morbidelli et al., 2000).”

“Meteoritic evidence is consistent with planetesimals forming early, with Schiller et al. (2015) suggesting that differentiated bodies formed only 0.25 Myr after calcium-aluminumrich inclusions, but little is known empirically about the radial profile beyond the general observation that the Solar System, and debris dis…”

“tween large planetary embryos and most likely possessed a globally molten magma ocean (e.g., Elkins-Tanton (2012)). According to Gillmann et al. (2009) and the terrestrial planet formation studies of Morbidelli et al. (2000) and Raymond et al. (2006), the equivalent of up to two terrestrial water oceans (TO) may have…”

“[3] have shown that a significant fraction of the Earth’s mass could be accreted late as a result of collisions with asteroids originating in the Main Belt.”

“I NOUE College of General Education, Osaka Sangyo University, 3-1-1, Nakagaito, Daito 574-8530 akinoue@las.osaka-sandai.ac.jp Mitsuhiko HONDA Department of Information Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 257-0031 hondamt@kanagawa-u.ac.jp Taishi NAKAMOTO and Akinori OKA Department of Earth…”

“…chemical nature of the lunar basin-forming impactors is important because, in addition to sculpting the surface of the Moon, the same population of impactors may have delivered substantial water and organic material to the Earth (Chyba et al., 1990; Morbidelli et al., 2000; Kobayashi et al., 2004).”

“In this model, the volatiles participated in the core-formation process at Earth’s magma ocean conditions [127 ,135 –137 ].”

“…more rigorous system indicators, such as the radial mass concentration and the 3 It has been suggested that after Venus formation, the planet probably had a WMF at least comparable to Earth’s current ocean mass (~2.5 10-4) (e.g., Morbidelli et al. 2000; Kulikov et al. 2006; Hashimoto et al. 2008).”

“…et al. 1996), and remnants of a cometary shower in terrestrial sediments (Farley et al. 1998), strongly suggest that gas-rich extraterrestrial material delivered volatile elements to the surface of the Earth from accretionary stages to the present (e.g., Chyba 1990; Morbidelli et al. 2000).”

“Both the Moon and Mercury provide relatively unweathered surfaces in comparison with the Earth, so their near-surface volatile inventories provide additional constraints on models of water delivery to the inner solar system.”

“• A significant fraction (∼ 10–20%) of the mass of the terrestrial planets is accreted from the outer part of the asteroid belt, which provides a formidable mechanism to explain the delivery of water to the Earth (Morbidelli et al., 2000; Raymond et al., 2004, 2007).”

“Recent dynamical models of the early Solar System (Morbidelli et al., 2000), and recent measurements of the D/H in cometary water (to be compared with D/H in the oceans (SMOW)) (Dauphas et al.”

“If most of Earth’s water is delivered from the planetesimal carbonaceous chondrite parent bodies, then the D/H ratio of Earth’s water is naturally explained (see Morbidelli et al., 2000, for greater detail and a discussion of the less likely alternatives).”

“Several hypotheses have been put forward, among which delivery by comets and/or asteroids during the so-called ‘late veneer’ stage (Morbidelli et al. 2000; Cleeves et al. 2014), direct adsorption of water onto grains prior to planetary accretion (Muralidharan et al. 2008), and in the recent ‘Grand…”

“If we compare these enrichment factors with the fraction of the Earth’s mass represented by water, i.e., 5 × 10−4 [64], we can immediately see that the scenario of no migration of Jupiter could result in a primordial Vesta as enriched in water as the Earth.”

“Our estimate of the migration of water to the early Earth is in accordance with [31], but is greater than those of Morbidelli et al. [ 32 ] and Levison et al. [33].”

“There is certainly evidence based on abundance analyses in our solar system that impacts from bodies in the asteroid belt or outer solar system have changed the surface abundances of the earth and other planets (e.g., Morbidelli et al. 2000; Gautier et al. 2001).”

“The Jovian planets also likely influenced the properties of Mars (Walsh et al. 2011) and the Earth, specifically related to the delivery of volatiles, the impact rates of minor bodies, and the development of life (e.g., Zahnle & Sleep 1997; Morbidelli et al. 2000; Horner et al. 2010).”

“…Earth obtained its primary volatiles (carbon, nitrogen and hydrogen/water), and the answer may include multiple sources, including a combination of cometary (Greenwood et al. 2011; Hartogh et al. 2011) and chondritic late impactors (Morbidelli et al. 2000; pontoppi@stsci.edu Tartèse & Anand 2013).”

“…due to the possibility that icy material from the main belt region could have been a significant primordial source of terrestrial water (e.g., Morbidelli et al., 2000; Raymond et al., 2004; O’Brien et al., 2006), and their potential as compositional probes of the early inner solar system in…”

“While Earth itself was accreted by materials from a mixture of chondritic sources and planetary precursors (Drake and Righter 2002; Marty et al. 2016; Morbidelli et al. 2000), Earth’s abundance and composition are incompatible with the originally volatile-rich disk materials from which it was built (Halliday 2013), su…”

“4 After Venus formation, the planet probably had a WMF on the order of Earth’s ocean mass (~10 4) (e.g., Morbidelli et al. 2000; Kulikov et al. 2006; Hashimoto et al. 2008; Greenwood et al. 2018).”

“Current planet formation models are at odds with the accretion of volatiles originating exclusively in the region of the solar nebula in which the planet is formed and favor the exogenous water scenario (e.g., Morbidelli et al. 2000; Walsh and Morbidelli 2011).”

“…are in stable orbits (Figure 2) (Wetherill 1990a,b, 1994, 1996; Kokubo & Ida 1995, 1998, 2007; Chambers & Wetherill 1998, 2001; Agnor et al. 1999; Morbidelli et al. 2000, 2012; Chambers 2001; Chambers & Cassen 2002; Levison & Agnor 2003; Raymond et al. 2004, 2005a,b, 2006b, 2007, 2009; Kokubo et…”

“This growth produced proto-planets (e.g., Boss, 2004; Raymond et al., 2004; Morbidelli et al., 2000).”

“This agrees with the second hypothesis which argues in agreement with previous theories for a water abundance more comparable to that on Earth and Mars (e.g., Wetherill, 1981; Morbidelli et al., 2000).”

“, Lebofsky, 1980; Rivkin, 2002; Takir & Emery, 2012; Vilas, 1994) and may have played a role in the transport of volatiles into the terrestrial planet forming region of the protoplanetary disk (Alexander, 2017; Alexander et al., 2012; Barnes et al., 2016; Marty, 2012; Morbidelli et al., 2000).”

“Depending on the specific mechanism involved, and whether or not the initial H-bearing reservoir was fractionated by subsequent processes (for instance, Denrichment due to hydrogen loss during the heating associated with accretionary growth of planetary bodies), the relatively D-poor composition proposed here in the i…”

“This condition is met in the Solar System, where Uranus is close enough to Neptune such that particles in the Kuiper belt with TNep 2.999 can be scattered by Uranus after a few encounters with Neptune (e.g., Levison & Duncan 1997).”

“Furthermore, icy planetesimals or comets may bring water to the Earth (e.g., Morbidelli et al. 2000).”

“Never-theless, given that the isotopic D/H ratios of ocean water and cometary water differ and the impact rate of comets was not that great, cometary H 2 O is little more than an admixture of the water on Earth (for a more detailed discussion, see Morbidelli et al ., 2000).”

“Note that in the Grand Tack model, the C-complex asteroids, which are thought to be carbonaceous chondrite parent bodies containing water that matches that of the Earth (Morbidelli et al., 2000; Alexander et al., 2012), are delivered to the Earth and the outer Main Belt from their initial locations at the inner edge o…”

“Some (e.g., Dauphas, Robert & Marty 2000; Morbidelli et al. 2000; Drake & Righter 2002; Robert 2001) consider the high D/H ratio in these comets as evidence against a cometary origin of most of the terrestrial water.”

“…blocks beyond the ice line on the other hand could be even more water-rich than our 5% (see O’Brien et al. 2018, and references therein), where for example 10% is not unreasonably high (for carbonaceous condrites, Morbidelli et al. 2000) and could have a large impact on final water inventories.”

“…system currently occupied by the present-day main asteroid belt may have played a significant role in the primordial delivery of water and other volatiles to the early Earth (Morbidelli et al. 2000; Raymond et al. 2004; Raymond & Izidoro 2017; O’Brien et al. 2006, 2018, and references within).”

“Using this model, Morbidelli et al. (2000) estimated that the asteroids could have barely delivered the required amount of water to Earth.”

“Our estimates agree with the constraints derived from recent dynamical models of the solar system (Morbidelli et al., 2000), and from mass-balance models based on D/H (Dauphas et al., 2000) or based on noble metals and gases (Dauphas and Marty, 2002).”

“es could provide the necessary low-D/H component of Earth’s water inventory. Our estimate of the migration of water to the early Earth is in accordance with Chyba (1989), but is greater than those of Morbidelli et al. (2000) and Levison et al. (2001). The latter obtained smaller values of M ice, and we suspect that th…”

“Possible sources include the comets (but the measured deuterium/hydrogen (D/H) ratios in the three that have been measured seems higher than in the oceans [109]) or watery asteroids like the MBCs ([112]).”

“…leftovers of planetary formation, which, through impacts, played an important role in the hydration process and the delivery of a variety of organic volatiles to the early Earth (see e.g. Owen & Bar-Nun 1995; Morbidelli et al. 2000; Horner et al. 2009; Hartogh et al. 2011; Snodgrass et al. 2017).”

“The water on both the Earth and Mars must in any case have been delivered long before the LHB – probably during the build-up phase of both planets (Morbidelli et al. 2000; Brasser 2013).”

“Critically, the positioning of the snow line in the asteroid belt implies that Earth did not acquire its water in situ (Morbidelli et al 2000).”

“Water must have been delivered to the surface of the Earth, potentially through asteroid impacts (Morbidelli et al. 2000; Raymond et al. 2007), even though comet collisions and the interaction between the magma and atmosphere have also been suggested as sources of the planet’s water (Lunine 2006;…”

“…that primitive asteroids probably played a strong role in the delivery of water and complex organic molecules to the early Earth (e.g., Morbidelli et al. 2000; Izidoro et al. 2013); currently, they also pose a special hazard to our planet because the most promising techniques to…”

“…was present in hydrous silicates in its primary building blocks, while another view advocates “dry” accretion, with water added in a “late veneer” during impact of hydrous asteroidal or cometary bodies (e.g., Morbidelli et al. 2000; Drake and Righter 2002; Albar ede 2009; Hartogh et al. 2011).”

“Because the orbital scattering becomes large only in the later stage of planetary accretion [Kokubo and Ida, 2000; Morbidelli et al., 2000], such a model would imply that water on Earth was acquired in the late stage of its accretion, say ~50-100 My after the”

“Geochemical and dynamic constraints suggest that <10 % of the Earth’s volatile budget was delivered by comets and that bodies from the outer main asteroid belt were the dominant source of primordial terrestrial organic molecules and water (Morbidelli et al. 2000; Gomes et al. 2005).”

“In one of the scenarios, water is thought to have been delivered to the Earth only after its formation, as the volatiles are lost during the formation (Morbidelli et al., 2000).”

“Morbidelli et al. (2000) showed that the bulk of Earth’s water was acreted by a few asteroidal embryos from beyond 2 - 2.5 AU while Raymond et al. (2007a) proposed that terrestrial planets acrete a comparable amount of water in the form of a few water-rich embryos and millions of planetesimals.”

“By providing evidence that ice exists in the present-day asteroid belt, they present an invaluable opportunity to evaluate hypotheses that icy main-belt objects may have played a significant role in the primordial delivery of terrestrial water (e.g., Morbidelli et al. 2000).”

“Primitive asteroids might harbor complex organic molecules and water that could have been delivered to the early Earth through collisions, contributing to the origin of life on our planet (Morbidelli et al. 2000; Izidoro et al. 2013).”

“…of these complex prebiotic organic compounds may have contributed to the origin of life on early Earth (Chyba and Sagan 1992; Owen and BarNun 1995; Morbidelli et al. 2000; Campins et al. 2010; Meteoritics & Planetary Science 50, Nr 10, 1684–1696 (2015) doi: 10.1111/maps.12498 1684© The…”