Ancient zircon crystals found in Western Australia may force humanity to rewrite Earth’s history.
Previous descriptions mostly assumed that until the end of the Hadean Eon, which lasted from 4.6 billion years ago to 3.8 billion years ago, Earth was a scorching, fiery sphere devoid of life.
However, a new study indicates that even during this period once believed to be “hellish,” key elements for life as we know it today were already in place: Freshwater and continents.
Jack Hills region in Western Australia, home to the oldest evidence of Earth’s history.
Presenting their findings at the European Geological Union conference, a group of geologists from various institutes and universities in Australia, China, and the United Arab Emirates (UAE) revealed that 4 billion years is the actual age of the first continents on Earth.
The composition of early Earth has long puzzled scientists. When our planet first formed 4.6 billion years ago, it was a swirling magma sphere.
What transpired during the Hadean Eon remains largely unclear. While we know that magma eventually solidified to form the crust, we do not know exactly when this occurred or what followed.
Some scientists suggest that Earth may have been largely covered by water as far back as 4.4 billion years ago, aligning with the discovery of the oldest zircons.
However, it is unclear how water arrived. It could have been part of the planet’s original composition or the result of bombardment by water-rich asteroids shortly after formation.
And freshwater is a whole other, much more complex story.
The existence of freshwater indicates that a hydrological cycle—evaporation and precipitation—had begun. Water without minerals accumulated on the uplifted portions of the continental crust, evaporating more easily due to its lighter isotopes compared to seawater, then reformed as rain and fell back to the surface.
This was demonstrated through zircon crystals extracted from rocks at the Jack Hills site in Western Australia, which once bore traces of the earliest microorganisms.
These zircons exhibit characteristics suggesting they formed when magma rose to the surface and interacted with freshwater.
These zircons were inadvertently mixed into some 3 billion-year-old rocks in Jack Hills and have been preserved to this day, as this unique area appears to have been undisturbed by geological activity for billions of years.
Due to their resilience, zircons are extremely useful in determining the exact time when continental plates formed as the crust began to intrude upon the global ocean surface.
And the age of 4.03 billion years and the properties of these crystals affirm that just 600 million years after formation, Earth had continents capable of storing freshwater on its surface.
This suggests that our planet may have evolved faster than previously thought, and supports earlier evidence indicating that the first life forms may have emerged while the Hadean Eon “hell” was still ongoing.
