Grant: Discovery Grants Program - Individual

Over the past 5 years, new evidence has been gathered regarding the very young Earth. It proves that our planet started to differentiate into metal, mantle and crust surprisingly soon after its final assembly. Although there is unanimous agreement about early differentiation, opinions range between two extreme viewpoints regarding the way in which the planet started to take shape. ) On the one extreme is the strict uniformitarian view, according to which the Earth's main geological processes of today pretty much operated 4.4 billion years ago. This concept, also known as the 'cool early Earth model', proposes that the familiar concept of plate tectonics was the main driving force behind planetary cooling. On the other extreme is the view that the early Earth was an inhospitable place whose atmosphere was filled with methane and whose surface was constantly covered in abundant mafic volcanic rocks, culminating in an event known as the late heavy meteorite bombardment. Here I identify several areas of research that will aim to provide new evidence to help resolve these conflicting views. ) First, we need to get a better handle on the age of the Moon because this will allow us to date the last step in the assembly of the Earth via the giant impact. My idea is to combine argon and lead isotope evidence to tease out a more precise minimum age of the Moon and the Earth. ) Second, we need to better understand how quickly metal cores formed on planetary precursors. There is a suite of meteorites (eucrites) that have been studied with hafnium-tungsten isotope systematics. The results are published but uncertainty about metal segregation time remains because we don't understand the geochemical behavior of tungsten well enough. This can be remedied with a study of modern mantle melts. ) Third, to everybody's surprise, some of the oldest zircon minerals on Earth were found to contain diamond inclusions. Is it possible that these diamonds formed when the early Earth was battered with meteorites, just as the Moon was? Or were these zircons formed deep in the Earth's interior? We need to know and we can study the Sudbury impact basin as an analogue for the early Earth.