@article {Deng2023,
	title = {Earth{\textquoteright}s evolving geodynamic regime recorded by titanium isotopes},
	journal = {Nature},
	volume = {621},
	number = {7977},
	year = {2023},
	month = {sep},
	pages = {100{\textendash}104},
	publisher = {Springer US},
	abstract = {Earth\&$\#$039;s mantle has a two-layered structure, with the upper and lower mantle domains separated by a seismic discontinuity at about 660 km (refs. 1,2 ). The extent of mass transfer between these mantle domains throughout Earth\&$\#$039;s history is, however, poorly understood. Continental crust extraction results in Ti-stable isotopic fractionation, producing isotopically light melting residues 3{\textendash}7 . Mantle recycling of these components can impart Ti isotope variability that is trackable in deep time. We report ultrahigh-precision 49 Ti/ 47 Ti ratios for chondrites, ancient terrestrial mantle-derived lavas ranging from 3.8 to 2.0 billion years ago (Ga) and modern ocean island basalts (OIBs). Our new Ti bulk silicate Earth (BSE) estimate based on chondrites is 0.052 {\textpm} 0.006{\textperthousand} heavier than the modern upper mantle sampled by normal mid-ocean ridge basalts (N-MORBs). The 49 Ti/ 47 Ti ratio of Earth\&$\#$039;s upper mantle was chondritic before 3.5 Ga and evolved to a N-MORB-like composition between approximately 3.5 and 2.7 Ga, establishing that more continental crust was extracted during this epoch. The +0.052 {\textpm} 0.006{\textperthousand} offset between BSE and N-MORBs requires that \&lt;30\% of Earth\&$\#$039;s mantle equilibrated with recycled crustal material, implying limited mass exchange between the upper and lower mantle and, therefore, preservation of a primordial lower-mantle reservoir for most of Earth\&$\#$039;s geologic history. Modern OIBs record variable 49 Ti/ 47 Ti ratios ranging from chondritic to N-MORBs compositions, indicating continuing disruption of Earth\&$\#$039;s primordial mantle. Thus, modern-style plate tectonics with high mass transfer between the upper and lower mantle only represents a recent feature of Earth\&$\#$039;s history.},
	issn = {0028-0836},
	doi = {10.1038/s41586-023-06304-0},
	url = {https://www.nature.com/articles/s41586-023-06304-0},
	author = {Deng, Zhengbin and Schiller, Martin and Jackson, Matthew G. and Millet, Marc-Alban and Pan, Lu and Nikolajsen, Katrine and Saji, Nikitha S. and Huang, Dongyang and Bizzarro, Martin}
}
