Earth's continental crust today is both created and destroyed by plate tectonic processes, a balance that is encapsulated by the traditional Chinese concept of yin–yang, whereby dualities act in concert as well as in opposition. Yin–yang conceptualizations of crustal growth and destruction are mostly related to plate tectonics; both occur mostly at subduction zones, by arc magmatic creation and by subduction removal. Crust is also created and destroyed by processes unrelated to plate tectonics, including losses by lower crust foundering and additions at hotspots. At present, creation and destruction of continental crust is either in balance (∼3.2 km³/year, or 3.2 AU) or more crust is being destroyed than created; the uncertainty comes from unknown deep losses of continental crust at collision zones and due to lower crustal foundering. The yin–yang creation–destruction balance changes over a supercontinent cycle, with crustal growth being greatest during supercontinent break-up due to high magmatic flux at new arcs and crustal destruction being greatest during supercontinent amalgamation due to subduction of continental material and increased sediment flux due to orogenic uplift. These conclusions challenge the widely held view that continental crust volume has increased over time due to plate tectonic activity; it is just as likely that this volume has decreased.

To understand how plate tectonics became Earth's dominant mode of convection, we need to address three related problems. (i) What was Earth's tectonic regime before the present episode of plate tectonics began? (ii) Given the preceding tectonic regime, how did plate tectonics become established? (iii) When did the present episode of plate tectonics begin? The tripartite nature of the problem complicates solving it, but, when we have all three answers, the requisite consilience will provide greater confidence than if we only focus on the long-standing question of when did plate tectonics begin? Earth probably experienced episodes of magma ocean, heat-pipe, and increasingly sluggish single lid magmatotectonism. In this effort we should consider all possible scenarios and lines of evidence. As we address these questions, we should acknowledge there were probably multiple episodes of plate tectonic and non-plate tectonic convective styles on Earth. Non-plate tectonic styles were probably dominated by ‘single lid tectonics’ and this evolved as Earth cooled and its lithosphere thickened. Evidence from the rock record indicates that the modern episode of plate tectonics began in Neoproterozoic time. A Neoproterozoic transition from single lid to plate tectonics also explains kimberlite ages, the Neoproterozoic climate crisis and the Neoproterozoic acceleration of evolution. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics’.

To better understand Earth's present tectonic style–plate tectonics–and how it may have evolved from single plate (stagnant lid) tectonics, it is instructive to consider how common it is among similar bodies in the Solar System. Plate tectonics is a style of convection for an active planetoid where lid fragment (plate) motions reflect sinking of dense lithosphere in subduction zones, causing upwelling of asthenosphere at divergent plate boundaries and accompanied by focused upwellings, or mantle plumes; any other tectonic style is usefully called “stagnant lid” or “fragmented lid”. In 2015 humanity completed a 50+ year effort to survey the 30 largest planets, asteroids, satellites, and inner Kuiper Belt objects, which we informally call “planetoids” and use especially images of these bodies to infer their tectonic activity. The four largest planetoids are enveloped in gas and ice (Jupiter, Saturn, Uranus, and Neptune) and are not considered. The other 26 planetoids range in mass over 5 orders of magnitude and in diameter over 2 orders of magnitude, from massive Earth down to tiny Proteus; these bodies also range widely in density, from 1000 to 5500 kg/m3. A gap separates 8 silicate planetoids with ρ = 3000 kg/m3 or greater from 20 icy planetoids (including the gaseous and icy giant planets) with ρ = 2200 kg/m3 or less. We define the “Tectonic Activity Index” (TAI), scoring each body from 0 to 3 based on evidence for recent volcanism, deformation, and resurfacing (inferred from impact crater density). Nine planetoids with TAI = 2 or greater are interpreted to be tectonically and convectively active whereas 17 with TAI <2 are inferred to be tectonically dead. We further infer that active planetoids have lithospheres or icy shells overlying asthenosphere or water/weak ice. TAI of silicate (rocky) planetoids positively correlates with their inferred Rayleigh number. We conclude that some type of stagnant lid tectonics is the dominant mode of heat loss and that plate tectonics is unusual. To make progress understanding Earth's tectonic history and the tectonic style of active exoplanets, we need to better understand the range and controls of active stagnant lid tectonics