# ▶︎ CANCELED: Dix Planetary Science Seminar

Tuesday, March 17, 2020
4:20pm to 5:00pm
Abstract: Only 3% of Earth's surface consists of land antipodal to land. This antipodal anticorrelation'' or odd-l dominance has characterized Earth's topographic power spectrum since at least the assembly and break-up of Pangaea. We present evidence in support of the hypothesis that antipodal anticorrelation is an emergent property of Earth's mantle convection style of plate tectonics. Venus also displays antipodal anticorrelation, albeit with muted elevation variations and muted odd-l dominance compared with Earth. We interpret this as possible evidence that Venus previously had plate tectonics, only to lose them following a period where its surface water evaporated rapidly. A posited transition from an ocean to a steam-dominated atmosphere would produce a pulse of substantial surface erosion, followed by gradual or episodic resurfacing associated with stagnant-lid convection. Our simple models of this process suggest that the transition occurred ~1 Gyr ago. We discuss a near-term test of our hypothesis: K-Pg style asteroid impacts onto a Venus with a ~1-bar atmosphere produce substantial delivery of minimally shocked material to the lunar surface. Our N-body simulations show that 4e-4% of material spalled from Venus ends up on the Moon. We argue that zircons in lunar regolith samples can be assayed for potential Venusian origin and age-dated. We estimate that such specimens constitute ~0.1% of the recoverable zircons within regolith samples.