Crystals almost as old as Earth itself
In 1981, professor Ajit Kumar Saha and his associates (colleagues and senior research students) at Presidency College, Calcutta, published a paper in the journal Science, claiming to have found rocks in Champua, Orissa, that were about 3,800 million (3.8 billion) years old.
The global geological community was sceptical. The rocks were probably old, but could they be that old? Experts from across India and around the world began to head to Orissa. In 2000, Rajat Mazumder, then a lecturer in Kolkata, started focusing on these rocks. In 2010, he was joined by Trisrota Chaudhuri, 35, then with the Indian Statistical Institute. “We were confident the rocks were even older,” says Mazumder, 53, now an associate professor at the German University of Technology in Oman.
They were right. In 2018, they published a paper in the journal Scientific Reports on two zircon crystals they extracted from rocks taken from the Champua site. While the rocks were 3.4 billion years old, the crystals were much older, at an estimated 4 and 4.2 billion years old. It has since been established that these zircons, along with others from the Acasta Gneiss in Canada and the Jack Hills in Australia (both about 4.4 billion years old) are the oldest recorded minerals in known geological history.
Excerpts from an interview with Mazumder and Chaudhuri.
What do the zircons you found in Champua tell us about early earth?
Chaudhuri: The first 500 million years of earth’s history, the Hadean Eon, was truly “hellish”. Asteroids constantly bombarded the earth and the surface was covered by an ocean of lava. Temperatures were so high (over 2,000 degrees C) that rocks vapourised.
The Hadean is considered a “dark age” in geological history because we know very little about this time.
It was earlier believed that the surface was nearly homogeneous at this time. Studies like ours suggest that, despite the extreme conditions, some parts of Earth’s surface started producing rocks somewhat similar to modern-day rocks, which survived. It also suggests that the production of such rocks began much earlier than previously estimated.
Why are zircons so significant?
Mazumder: Zircon is a mineral formed by the crystallisation of magma from deep within the earth’s crust. Each crystal, generally less than 1 mm in size, is highly resistant and acts as a snapshot of geological events.
Chaudhuri: Zircons outlast the rocks that hosted them. It’s like a ripe fruit fallen on the ground. Eventually the soft flesh rots away but the seed remains, proving that the fruit was once there. No rock more than 4,000 million years old survives today. All the “oldest rocks” have only left behind traces of zircon, an extraordinarily robust mineral.
How does one date elements this old?
Chaudhuri: Zircons are probed in an instrument called the SHRIMP (Sensitive High Resolution Ion Microprobe). In our case, this stage was done by professor Yusheng Wan and others at the Beijing SHRIMP Centre. We pursued several renowned labs around the world before we reached them, but we could not convince the other labs that these rocks were worth looking into.
After our discovery, I contacted several government bodies and research institutes in India to sponsor further research, but have received no response. I have managed to secure funding from the Research Council of Oman to work on these rocks, but am currently looking for a collaborator from India.