Zircons Predates Origin of Earth
Economy, Sci & Tech

Zircons Predates Origin of Earth

Los Angeles is home to the world’s largest collection of Hadean zircons—the oldest known material on Earth.
Hadean zircons are tiny but they contain a huge amount of information about the earliest days of our planet.
The Hadean period began 4.5 billion years ago, when Earth was just 40 million or so years old. Scientists have long presumed it was a time of hellish conditions, characterized by scorching temperatures and molten rock. But the zircons reveal a different story.
According to the Los Angeles Times, chemical signatures embedded in the crystals suggest the planet had water, continents and even interconnected oceans.
This month, researchers studying these zircons made an even more unexpected discovery: The first evidence that life may have existed 4.1 billion years ago. That’s 300 million years earlier than was previously thought.
“Open any textbook and you see all these assumptions about the early Earth—it had no water, it had no continents,” said UCLA geochemist Mark Harrison, the guardian of zircons. “Yet every bit of evidence suggests it was much more like today than anyone imagined.”
Harrison has been studying zircons for 20 years and over that time he has amassed a collection of more than 180,000 of the tiny crystals. The oldest specimens in his archive—the Hadean zircons—have remained chemically unchanged for at least 4 billion years. Some of them formed just 100 million years after Earth was born.
The evidence of possible life from 4.1 billion years ago did not come from the zircons themselves, but from tiny slivers of carbon embedded in the crystals.
The study’s results were published this month in the Proceedings of the National Academy of Sciences.
The earliest microfossils suggest that there was life on Earth 3.5 billion years ago. Prior to this study, the earliest evidence of life based on a carbon signature was from 3.8 billion years ago.
Experts say that although the work does not prove there was life on early Earth, it does offer an intriguing new way to approach the question of when life on Earth first came to be.


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