Formation of the Earth

Calcium-aluminum inclusions (CAI) in chondritic meteorites are the oldest solid components that formed from the solar nebula. They consist of minerals such as anorthite, melilite, spinel, and perovskite, and have been estimated to be 4567.30 ± 0.16 Ma using the Pb-Pb method (Amelin et al. 2010) = age of the solar system.

Determining the age of the Earth is difficult because plate tectonics has resulted in very little material being available today. Therefore, undifferentiated, chondritic meteorites are used, which have a similar composition to the bulk Earth. Lead-lead dating yielded an age of 4550 ± 70 Ma (Patterson 1956).

The Earth initially existed as a partial or complete magma ocean (depending on the model), with cooling being prevented by (1) impacts (e.g. LHB: Late Heavy Bombardment), (2) radioactive decay of short-lived isotopes (e.g. ²⁶ Al → ²⁶ Mg), (3) gravitational contraction, and (4) heat of crystallization and differentiation.

The differentiation of Earth into a metallic core and silicate mantle lasted until approximately 30–50 myr (Hf-W age) after the formation of the solar system (Rubie et al. 2007). The complete formation of smaller planetary objects took less than 1 myr, while terrestrial planets required up to 100 myr (Kleine et al. 2009).

Approximately 62 ⁺⁹⁰ _-10 Myr after CAI (Hf-W; Touboul et al. 2007), a Mars-sized protoplanet (Theia) collided with Earth. This resulted in a change in Earth's rotational axis to 23.5° (Halliday 2000) and the accretion of the Moon from the debris cloud.
Other impacts also led to the enrichment of HSE (Highly Siderophile Elements) → Late Veneer Event (dated to > 100 Myr according to CAI). However, complete homogenization of the HSE took until approximately 3800 Ma (Li 2022).

It is unknown when the first solid Earth's crust formed (no relics remain today due to plate tectonics). The oldest rock unit is the Acasta Gneiss (tonalitic gneiss of a TTG), which covers an area of ​​< 1 ^km² (Carlson et al. 2019) in the Canadian Slave Craton and yielded U-Pb ages of 4019.6 ± 1.8 Ma (Reining et al. 2016).

The oldest terrestrial material consists of zircon grains from a 3000 Ma old quartzite in the Australian Yilgarn Craton (Jack Hills) with a U-Pb age of 4374 ± 6 Ma (Valley et al. 2014). The following observations can be made on them.

1. Highly variable εHf values ​​(strongly negative to positive) suggest a mixture of magma from older, molten, continental (enriched) crust and juvenile (chondritic) mantle (Bell et al. 2014).

2. O isotopes also confirm the presence of water in the old recycled crustal material [either hydrosphere (ocean) or atmosphere enriched with water vapor (Mojzsis et al. 2001)].

3. It is controversial whether JH zircons prove early plate tectonics (subduction zones) (Turner et al. 2020).

Apart from the Acasta and Jack Hills material, most Archean rocks/minerals show a chondritic initial isotopic composition (e.g., εHf _(i) ), which proves that the Earth's crust formed directly from the primitive mantle during the Archean, without recycling older crust (Salerno et al. 2021). Only in rock signatures from 3800–3600 Ma does a clearly positive _εHf(i) trend of a depleted mantle become apparent, meaning that enriched, continental crust was extracted from the primitive mantle only about 700 Myr after Earth's formation (Vervoort & Kemp 2025). However, other models with increased mantle mixing rates can explain a continental crust and a depleted mantle as early as the Hadean (Guo & Korenaga 2023).

literature

Amelin, Y., Kaltenbach, A., Iizuka, T., Stirling, CH, Ireland, TR, Petaev, M., & Jacobsen, SB (2010). U–Pb chronology of the Solar System's oldest solids with variable 238U/235U. Earth and Planetary Science Letters , 300 (3-4), 343-350.

Bell, EA, Harrison, TM, Kohl, IE, & Young, ED (2014). Eoarchean crustal evolution of the Jack Hills zircon source and loss of Hadean crust. Geochimica et Cosmochimica Acta , 146 , 27-42.

Carlson, RW, Garçon, M., O'neil, J., Reimink, J., & Rizo, H. (2019). The nature of Earth's first crust. Chemical Geology , 530 , 119321.

Guo, M., & Korenaga, J. (2023). The combined Hf and Nd isotope evolution of the depleted mantle requires Hadean continental formation. Science Advances , 9 (12), eade2711.

Halliday, AN (2000). Terrestrial accretion rates and the origin of the Moon. Earth and Planetary Science Letters , 176 (1), 17-30.

Kleine, T., Touboul, M., Bourdon, B., Nimmo, F., Mezger, K., Palme, H., ... & Halliday, AN (2009). Hf–W chronology of the accretion and early evolution of asteroids and terrestrial planets. Geochimica et Cosmochimica Acta , 73 (17), 5150-5188.

Li, C. H. (2022). Late veneer and the origins of volatiles of Earth. Acta Geochimica , 41 (4), 650-664.

Mojzsis, SJ, Harrison, TM, & Pidgeon, RT (2001). Oxygen-isotope evidence from ancient zircons for liquid water at the Earth's surface 4,300 Myr ago. Nature , 409 (6817), 178-181.

Patterson, C. (1956). Age of meteorites and the earth. Geochimica et Cosmochimica Acta , 10 (4), 230-237.

Reimink, JR, Davies, JHFL, Chacko, T., Stern, RA, Heaman, LM, Sarkar, C., ... & Pearson, DG (2016). No evidence for Hadean continental crust within Earth's oldest evolved rock unit. Nature Geoscience , 9 (10), 777-780.

Rubie, D.C., Nimmo, F., & Melosh, H.J. (2007). Formation of Earth's core. Evolution of the Earth, 9, 51-90.

Salerno, R., Vervoort, J., Fisher, C., Kemp, A., & Roberts, N. (2021). The coupled Hf-Nd isotope record of the early Earth in the Pilbara Craton. Earth and Planetary Science Letters , 572 , 117139.

Touboul, M., Kleine, T., Bourdon, B., Palme, H., & Wieler, R. (2007). Late formation and prolonged differentiation of the Moon inferred from W isotopes in lunar metals. Nature , 450 (7173), 1206-1209.

Turner, S., Wilde, S., Wörner, G., Schaefer, B., & Lai, YJ (2020). An andesitic source for Jack Hills zircon supports onset of plate tectonics in the Hadean. Nature Communications , 11 (1), 1241.

Valley, JW, Cavosie, AJ, Ushikubo, T., Reinhard, DA, Lawrence, DF, Larson, DJ, ... & Spicuzza, MJ (2014). Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography. Nature Geoscience , 7 (3), 219-223.

Vervoort, J.D., & Kemp, A.I. (2025). Isotope Evolution of the Depleted Mantle. Annual Review of Earth and Planetary Sciences , 53 .