ScAm

56 Scientific American, April 2020

parts of the world, it does not accumulate in soils,

because rain washes it away. But in dry places, like the

Transantarctic Mountains, it can build up over millen-

nia, until it reaches toxic levels. These high places also

accumulate perchlorate, an oxidizing chemical used in

disinfectants and rocket propellants—and famous, as

discovered by the Phoenix Mars Lander, for making

the surface of that planet an unpleasant place.

The salts create a catch-22 for small animals such as

springtails trying to escape advancing glaciers: remain-

ing in place means they will become buried underneath

ice, but creeping uphill leads to places that are “just nas-

ty, toxic,” Adams says. “Really crappy habitat.”

Sure enough, Hogg and Adams only found spring-

tails living below the trimline. These places, however,

would have been covered by 100 meters or more of ice

at the last glacial maximum, and it would have been

impossible for complex life-forms such as Tullbergia to

survive in ice for tens of thousands of years. So where

did the animals go?

HISTORY REWRITTEN

tHe survival of any animal depends on water, and water

seems to point to an explanation for Tullbergia’ s unlike-

ly endurance.

Seven hundred kilometers northwest of Shackleton

Glacier the Transantarctic Mountains emerge from the

interior of the continent and begin to run along the coast-

line. This is where the isolated McMurdo Dry Valleys are.

Despite the dryness, several of the valleys hold ice-cov-

ered lakes, fed by summer meltwater. The lakes are only

a few meters deep, yet high up on a few of the valley walls

are bathtub rings—ancient shorelines of sand and grav-

el. They suggest that some of these valleys had once held

WHITE AND
BRISTLY when
alive, Tullbergia
quickly dries out
and dies when
exposed to air.
On this individu­
al’s remains—
stained with dye
and greatly en ­
larged—the
hard exo skele­
ton ap pears red;
the softer, cuti­
clelike mem ­
brane looks
green. Two eye ­
holes are visible
at the base of
the antennae
(top image).

© 2020 Scientific American © 2020 Scientific American