The End of Earthly Oceans - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 208

high and variable temperatures, intense sunlight, and high UV radi-
ation (in a low-oxygen future Earth, the protective ozone layer would
no longer be present). These last ocean communities may resemble,
perhaps, the microbial mats that form around black smokers—
regions on the sea floor through which hot volcanic waters gush
today—or like those in the crater lakes of the volcanoes in the high
Atacama Desert of Chile.
Runaway Earth
James Kasting's models revealed a further state, if temperatures were
to ratchet yet higher, such that the oceans began to boil. In this state,
as water rapidly converts to steam the atmosphere fills with water
vapour faster than it can be lost at the top of the stratosphere. This is
the fearsome state known as a runaway greenhouse world. Its high-
pressure steam atmosphere will become a super-efficient insulation
blanket. Sunlight will get in, but very little heat will escape.
On this runaway world, temperatures could rise to something near
1,200 degrees Celsius, hot enough for rocks to melt. 122 A magma ocean
would form at the Earth's surface. This is the kind of fate that Venus is
thought to have suffered a long time ago (Chapter 9). Temperatures
will only begin to drop once all the water had gone.
A post-runaway world of this kind would look very different to one
in which only a moist greenhouse had operated. Its hard, fused sur-
face would likely look like that following the cooling of one of the
more fluidal volcanic lavas—smoothed, shiny, perhaps wrinkled or
cast into rope-like shapes here and there, with smoothly sculpted
hills separated by flat-floored valleys into which the molten rock had
puddled. There would be no soil, no sand, no sediment of any kind,
other than perhaps the barely recognizable traces of some of the larg-
est boulders. Much of the landscape would be blackened, rather like
obsidian, with here and there some paler patches—for instance where