origins of life Flashcards
how did the moon form?
by collision of a Mars sized embryo ‘Theia’ with the earth at a late stage of accretion, 40-70 myr after the start after the earth’s core had formed
why has the moon been receding?
the angular momentum is transferred from the earth’s spin to the moon via tidal breaking
what is outgassing?
- some elements in the earth’s mantle reacted to form compounds that could solidify
- they were outgassed to the surface to form part of the oceans and atm
- the moon forming impact would have created a short-lived rock vapour atm which condensed then left behind an initially hot CO2 and water atm
what do extraterrestrial impacts create?
earth water and atm
what is a zircon?
a common mineral found in tiny crystals
what happens when a zircon solidifies?
lead is rejected but impurities of uranium are present
what happens to the uranium impurities when a zircon solidifies?
the 2 isotopes decay to 2 isotopes of lead with different half-lives, allowing cross-checking of dating
where are zircons found?
siliceous igneous rock, like granite
where are the oldest rocks found?
NW Canada, Acosta Gneiss
when was the late heavy bombardment?
3.9 Ga
when was the Archean?
3.8-2.5 Ga
what isotope indicates carbon fixation by rubisco?
S^13C
when did life begin?
3.8-3.3 Ga
