70 Science and technology The EconomistJune 9th 2018
2
EvolutionAnimal magic
D
URING the Cambrian period, which
began 541m years ago, animal life
took a remarkable leap forward. The first
creatures believed by most (though not
all) palaeontologists to be multicellular
animals appear in the previous geologi-
cal period, the Ediacaran. But though
they are abundant and reasonably di-
verse, Ediacaran creatures do not look
ancestral to modern animals. That is in
contradistinction to Cambrian fossils,
among which are found representatives
of all the main animalgroups (annelids,
arthropods, brachiopods, chordates,
cnidarians, echinoderms, molluscs and
so on) that are around today. And these
groups appear in what is, in geological
terms, an eyeblink.
Several explanations have been put
forward to explain the Cambrian explo-
sion of animal life. One of the most pop-
ular is that it was fuelled by a dramatic
rise in oxygen levels, permitting large and
active creatures to thrive. However, a
study just published inGeologyby Wei
Guangyi of Nanjing University suggests
this tale is not true. Though oxygen levels
certainly did rise in the late Ediacaran
and early Cambrian, he and his col-
leagues suggest that what propelled
animal evolution was actually two occa-
sions when they crashed.
Dr Wei’s evidence comes from rocks
in the Chinese provinces of Hubei and
Yunnan. Specifically, he and his col-
leagues looked at uranium in limestone
that had formed in shallow Ediacaran
and Cambrian seas. Uranium has two
isotopes,^235 Uand^238 U, that differ by three
in the number of neutrons in their nuclei.
This small mass difference is enough to
affect the speed of chemical reactionsinvolving them, particularly if those
reactions are biologically mediated by,
say, bacteria, and thus involve inter-
actions with enzymes. The upshot is that
uranium compounds precipitated in
well-oxygenated water have more^238 U in
them than those from anoxic water.
Armed with this information, Dr Wei
and his colleagues looked at the ratio of
uranium isotopes in their rock samples
and found two moments when^238 U
levels plunged with respect to those of(^235) U. The first was between 542m years
and 541m years ago—that is, immediately
before the Cambrian. The second was
between 524m years and 523m years ago,
after the Cambrian had been going for
some time. Crucially, these dates match
what look, from the fossil record, like two
pulses of evolution in the history of the
animals. The first saw the emergence of
brachiopods and molluscs, the second
that of annelids, cnidarians, echino-
derms and chordates (a group that in-
cludes the vertebrates).
In Dr Wei’s view, then, what hap-
pened in the Cambrian was similar to
subsequent incidents of biological diver-
sification, such as that of the mammals
after the extinction of the dinosaurs. First,
some sort of environmental catastrophe
wiped out many of the previous in-
cumbents. Then, new groups emerged to
fill the empty ecological niches. In the
case of the dinosaurs, the catastrophe
was an asteroid impact. In the case of the
Cambrian it was periods of anoxia of
as-yet-unknown cause. It remains true
that rising oxygen levels on Earth at the
time were necessary to permit animals to
prosper. But the trigger for their diversity
may well have been the reverse.
The Cambrian explosion was caused by a lack of oxygen, not an abundance
Creatures from the black lagoon
of carbon dioxide a year.
Factoring in operating costs and the cost
of capital, the study concludes that Carbon
Engineering’s system could capture a
tonne of the greenhouse gas for between
$94 and $232. That is well below the $600
per tonne suggested by authors of an influ-
ential American Physical Society report
from 2011 that reviewed proposed carbon-
dioxide-removal schemes. Admittedly, it is
still much pricier than the $10 or so that a
tonne of the gas is worth in emissions-trad-
ing schemes such as the European Union’s.
But it is of the order of the $100 or so that
most climate economists think would
eventually be needed to prompt the transi-
tion to the low-carbon economy implicit in
the Paris agreement. And Dr Keith thinks
the cost can be brought down further with
a bit of tinkering.
Carbon Engineering and its investors
believe they can make money even before
this happens. To start with, revenue would
be generated by turning captured CO 2 back
into fuel (technology to do this already ex-
ists). Though that sounds thermodynami-
cally bonkers, such fuel would, from a legal
point of view, count as “zero carbon” be-
cause making and then using it involves no
net release of CO 2 into the atmosphere.
Demand for zero-carbon liquid fuels
looks poised to rise as climate-friendly
places adopt low-carbon fuel standards.
California did this in 2007 and the Euro-
pean Union followed in 2009. Such stan-
dards force distributorsto keep the average
carbon intensity of petrol below a certain
threshold, and therefore to offset dirty fu-
els with clean ones—and none is cleaner
than Carbon Engineering’s. California’s re-
quirement, which is in effect a cap-and-
trade scheme, translates to a price of $165
per tonne of carbon dioxide, making the
company’s product competitive. Steve
Oldham, the firm’s boss, therefore hopes
to license know-how to fuel producers do-
ing business in such jurisdictions. Mr Old-
ham says that ground should be broken on
the first industrial-scale plant, which is to
be built at an undisclosed location in
America, before the end of the year.
As both Dr Keith and Mr Oldham con-
cede, recycling CO 2 in this way means that
Carbon Engineering’s current business
model offers zero, rather than truly nega-
tive, emissions. But it gives the company
breathing space to fine-tune its system and
demonstrate its feasibility to investors.
More Gothenburg-like gatherings may yet
prompt governments to take negative
emissions seriously. California is already
considering subsidies for carbon-dioxide
removal. As things stand, the cost of using
Carbon Engineering’s kit to scrub
8bn-10bn tonnes of CO 2 per year, as the cli-
mate models presuppose, would run to
trillions of dollars. Then again, no one said
guaranteeing civilisation’s survival was
going to come cheap. 7