Open Magazine – August 07, 2018

34 6 august 2018

by rivers and streams and deposited into

other locations or simply gotten embed-

ded into other rocks, where they have

remained for billions of years until now.

These tiny zircon crystals have now be-

gun to tell us a very different story from

the one we have heard for so many years.

“We have always believed Earth was this

hot and hellish place 4 billion years back.

But some of these zircons, although it is

still debated, are telling us it may have

become cooler and wetter, even liveable

long before,” Chaudhuri says.

s tudies on ancient zircon crystals have

revealed several interesting things. They

have pointed to the presence of a stable

primordial crust on the earth’s surface

by 4.4 billion years ago and a distinctive

oxygen isotopic signature that indicates

the presence of water on Earth’s surface

by 4.3 billion years ago. This is far from the

picture painted of earth as a hot and mol-

ten world, which, let alone life, could not

even support a crust of solid rock.

all of this now leads to a larger ques-

tion. If Earth’s atmosphere had signifi-

cantly cooled for the presence of a stable

crust and for water, could life be far be-

hind? The most explosive study in this

field came in 2015, with the finding of a

4.1 billion-year-old biological signature

within a zircon’s chemical composition.

The journal Proceedings of the National

Academy of Sciences published a study

where researchers had found a 4.1 billion

year old zircon mineral with a chemical

composition that suggested organic life.

If true, it meant that our earliest ances-

tors—in their single-celled microbial

form—had emerged a long time before

anyone had thought possible. and this

emergence pre-dated the earliest undis-

puted fossil evidence for life—a fossil-

ised mat of single cell microbes called

stromatolites that grew in shallow seas

and was discovered in a sandstone rock

in australia—by 600 million years.

In this study, the researchers had found

tiny bits of potentially undisturbed graph-

ite, a form of carbon, in a single 4.1 billion-

year-old zircon crystal from Jack Hills in

Western australia. The graphite had a

higher ratio of carbon-12 (light atoms) to

carbon-13 (heavier ones). This suggests

that the carbon had been processed by

living organisms, because, according to

geochemists, some of these life forms tend

to incorporate more of the light carbon

and less of the heavy one.

The researchers have themselves

claimed that it is possible for non-biolog-

ical processes to lead to such an isotopic

ratio, but it is highly unlikely. “It’s not a

smoking gun for there being life at 4.1 bil-

lion years,” the lead researcher Elizabeth

Bell from the university of California

then told Los angeles Times. “But if you

saw that same isotopic signature on the

Earth today, you would say, ‘That is from

a biogenic source’.”

s

InCE THEn, THERE have been

few more studies that have hinted

at a very early emergence of life. some

australian researchers claimed to have

found 3.7-billion-year-old stromatolites,

or fossil remains of microbes, in 2016. Last

year, another group of researchers report-

ed finding 4.28-billion-year-old fossilised

microorganisms that once thrived under-

water around hydrothermal vents in the

nuvvuagittuq Belt, which consists of very

ancient rocks close to Quebec, Canada.

Earlier this year, another study, published

in Science Advances, found that two 4.5

billion-year-old meteorites which had

separately crashed to Earth back in 1998,

contained liquid water along with com-

plex organic substances (hydrocarbons

and amino acids) that may have been the

ingredients for life.

all of this is still hotly contested. This

early emergence of life—however tanta-

lising—is still at best a claim. It may hint

to an origin of life not as simple or recent

as we have believed. But it is still a ‘might

have been’ than a definite ‘life was here’.

o ur best bet to get to the root of all this,

Mazumdar says, lies in finding more of the

oldest materials on earth. Mazumdar and

Chaudhuri say this will be the next step

in their research. They will be looking for

more samples of ancient zircon crystals

in India and examining their oxygen and

carbon compositions for early signs of wa-

ter and perhaps even life. “Even if we find

water, it will be very significant. Because

wherever there is water, there is usually

life,” Chaudhuri says.

a ccording to Mazumdar, while there

are several capable geologists working

in India, very few international agencies

and researchers have attempted to look at

rocks in India. “If you search, you will defi-

nitely get more [zircons here],” Mazumdar

says. “But I think with this discovery [of

the second-oldest zircon in odisha], it will

intensify work in this field in India. I’m

sure geologists and the geological society

of India are already looking more intently

at Champua.” There is even talk of an in-

stitute, either an IIT or the gsI, he says, ac-

quiring a machine for isotopic analyses of

zircon minerals in India soon.

s o what are the chances of laying

one’s hands on a zircon mineral that con-

tains evidence of early life? “Look at the

australian study [the 2015 study of a 4.1

billion-year-old zircon carrying carbon

composition suggesting life]. It was a

freak finding. To find such a zircon with

such a carbon composition from among

thousands of samples was really lucky,”

Chaudhuri says. “and that’s one thing I

have learnt with our current discovery.

you need to be a sharp geologist, yes, but

also very lucky.” n

“we have believed earth was this hot and hellish

place 4 billion years back. but some of these zircons,

although it is still debated, tell us it may have become

cooler and wetter, even liveable long before”

Trisro Ta Chaudhuri, geologist

Geologists Trisrota Chaudhuri

(left) and Rajat Mazumdar

life