10 DISCOVERMAGAZINE.COM
Leading the 2018 challenge is Abigail Allwood, who identified
the oldest convincing stromatolites in Australia over a decade
ago. After reading about the newest “oldest” fossils in
Greenland, the NASA geologist wanted a look.
Allwood and colleagues visited the outcrop
for a day of field observations. “We went
open minded,” she recalls. But upon seeing
the surrounding geology, they decided the
rocks had been compressed one way and
elongated another — “stretched out like chewing
gum,” says Allwood. This formed features that resemble
stromatolites, but only when viewed head on.
The scientists collected a “wider, taller, deeper sample,”
about 1.5 feet from the area previously studied. Laboratory
analyses corroborated their field conclusion: Eons of geologic
activity squeezed and baked lifeless rocks into faux fossils.The original paper’s authors stand by their stromatolites. Led
by geologist Allen Nutman of the University of Wollongong,
Australia, they say Allwood sampled a poorly
preserved section. Nutman likens it to a rotting
apple: “If you want to study what an apple
actually is, you go look at the bits which are still
fresh, not the bits which are starting to decay.”
In the 2016 study, his team analyzed a well-
preserved portion and found features resembling
both kinds of stromatolite appearances (cones and
domes of layered sediment) and composition (chemical
elements consistent with seawater formation).
Nutman also notes that these ancient rocks are “some of
the most complicated and messy in the world to study.” If a
bunch of people fly in to examine them, he says, naturally
“there would be controversy and disagreement.”IT’S A MATTER OF LIFE OR NO LIFE.
In a 2016 Nature study, researchers
reported finding fossils in 3.7 billion-
year-old rocks in Greenland,
pushing the timeline for Earth’s
first preserved organisms back
200 million years.
But a 2018 paper, also in Nature,contended that the rock outcrop
preserves no signs of life.
The dispute concerns inch-high
layers of cones and domes embedded
in a section of rock recently exposed
by melting snow. The original team
interpreted them as stromatolites,
fossils formed in shallow seaswhen mats of microbes accumulate
sediment and minerals. Elsewhere
on Earth, stromatolites provide proof
of bacterial communities as old as
3.5 billion years. But the Greenland
humps are ambiguous. In Science
Smackdown, we let researchers
debate the evidence. — BRIDGET ALEXAre the
Oldest Fossils
Merely Rocks?
FOSSIL-FREE ROCKS LIFE WAS ONCE THEREThe Claim The Counterpoint
Scientists disagree about
whether a sample of ancient
rocks shows evidence of life.The triangular
shapes at the
bottom of this
Greenland rock
may be ancient
fossils — or not.SCIENCE SMACKDOWNTHE CRUX
CLOCKWISEFROMTOP:^COURTESYOF^ ABIGAILALLWOOD;^COURTESYOFALLEN^NUTMAN;^ SONJADESTERKE/QUT