Ocean Origins on Earth - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 20

the extent that the period of Earth history before Theia has been
suggested as a new eon, christened the Chaotian, 17 while the pre-
impact Earth itself, being a different planet, was also proposed a
new name, of Tellus. If the planet that was Tellus—a now unknow-
able planet—had possessed any significant volatiles (including
water), then most of these should have been vapourized and dis-
persed into space in the aftermath of the giant impact. Therefore, if
we start with an Earth constructed from metals and silicates at rela-
tively high surrounding temperatures, and then smash another
planet into it to remove what little water might have been originally
there—how did we get oceans?
One answer is—later.
From the Heavens
There are other things that are strange about the Earth's crust. Some-
thing has happened to its content of elements such as lead, indium,
and xenon, which are both volatile and have radioactive isotopes that
makes them function as atomic clocks. With all of these elements, the
'clocks' seem to have been reset about 100 million years after the
Earth formed.
The French geochemist Francis Albarède considers that these ele-
ments came from outer space, after the Earth had already formed. He
has proposed that the Earth, both in its primordial state and just after
the Theia impact, was essentially dry. The Earth's water, he suggests,
came subsequently from the skies after the Moon-forming event,
together with most of the Earth's crustal lead, indium, and xenon.
Other volatiles such as carbon and nitrogen likely hitched a ride to
Earth with these elements too, creating a 'late veneer' upon the Earth's
surface. The idea is not new, but was restated persuasively. 18
What, then, were the delivery capsules? Albarède's chosen vehicle
is a particular kind of meteorite, a carbonaceous chondrite, that is