Friday 25th October 2013 4.00 p.m. Professor Linda T. Elkins

Joint Physics/Earth Sciences Colloquium
Building Earth-like Planets:
from gas and dust to ocean worlds
The first Lobanov Lecture in Planetary Geology
Professor Linda T. Elkins-Tanton
Visiting Astor Lecturer, Earth Sciences, Oxford
Director, Department of Terrestrial Magnetism,Carnegie Institution of Washington
Friday 25th October 2013
4.00 p.m.
Martin Wood Lecture Theatre,
Clarendon Laboratory, Parks Road, Oxford
To begin to understand what makes a planet habitable, and thus where to look for life both within and outside
of Earth’s solar system, we need to understand what in planetary formation and what in its subsequent evolution
combine to produce a habitable planet. Though many things may help to make a habitable planet, only one
thing is indispensible: liquid water. Geochemical observations indicate that the bulk of Earth’s water came
from rocky planetesimals similar to asteroids. The accretionary impacts that add these materials to a growing
planet during the first tens of millions of years of the solar system, culminating with the giant Moon-forming
impact on Earth, had been thought to dry their target materials through heat and fragmentation. New mission
data from Mars, the Moon, and Mercury, however, all indicate that these bodies have water in their interiors
that originated with accretion, and so accretionary processes do not dry rocky planets. Models also indicate
that sufficient water existed on the early Earth, even immediately after the Moon-forming impact, to form
water oceans. Models further indicate that cooling and formation of an ocean occur very quickly, on the
order of 10 millions years or less. Though this first wet atmosphere may be partially lost through erosion by
an active young star, indications are that rocky planets accrete with water and may widely be expected to
form early water oceans and thus open the potential for early habitability.