How researchers found remains of the Earth’s primitive crust near Perth

Our planet was born about 4.5 billion years ago. To understand this long, amazing history, we need to study the rocks and minerals that compose it.

Australia’s oldest rocks, some of the oldest on Earth, were found in the Murchison region of Western Australia, 700 kilometers north of Perth. They have been dated to about 4 billion years ago.

In a new study published in Earth and Environment Communicationswe found Evidence of rocks of the same age Near Cooley, South Perth. This suggests that ancient rocks in Western Australia cover a much larger area than we knew, buried deep in the Earth’s crust.

Ancient continental crust

The ancient crust of Australia is crucial to understanding the early Earth, because it tells us about how the continental crust formed and evolved.

Continental crust forms the basis of the land masses on which humans live, supports ecosystems, and provides the basic resources for civilization. Without it there would be no fresh water. It is rich in mineral resources such as gold and iron, making it economically important.

However, exploring ancient continental crust is not easy. Most are deeply buried, or have been extensively modified by their environment. There are only a few exposed areas where researchers can observe this ancient crust directly.

To understand the age and composition of this hidden ancient crust, scientists often rely on indirect methods, such as studying eroded minerals preserved in covered basins, or using remote sensing of sound, magnetic, or gravity waves.

However, there may be another way to probe the deeper crust, and even sample it, if we’re lucky.

Pulling crystals from the depths

Our planet’s crust is frequently cut by dark fingers of iron- and magnesium-rich magma, which can extend from the upper crust all the way down to the Earth’s mantle. These structures, known as dikes, can come from depths of at least 50 kilometers (much deeper than even the deepest well, which extends just 12 kilometers).

These dams can capture small amounts of minerals from the depths and transport them to the surface, where we can examine them.

In our recent studyWe have discovered evidence of ancient buried rocks by dating zircon grains from one of these dykes.

Zircon contains trace amounts of uranium, which decays over time into lead. By carefully measuring the ratio of lead to uranium in zircon grains, we can know how long it has been since the grains crystallized.

This method showed that the zircon crystals from the dam date back to 3.44 billion years.

Titanite armor

Zircon is encapsulated in a different mineral called zirconium TitaniteIt is more chemically stable than the zircon found in dam. Think of a grain of salt trapped inside a piece of boiled sugar that you dropped into a cup of hot tea.

The stability of the titanium shield protected the ancient zircon crystals from changes in chemical conditions, pressure and temperature as the dike moved upward. The unprotected zircon crystals in the dam were significantly modified during the journey, obliterating their isotopic records.

However, the titanium armor grains survived intact providing a rare glimpse into Earth’s early history.

The dam, which dates back about 1.4 billion years, has provided a unique window into ancient crust that would otherwise have remained hidden. We also found similar ancient zircon grains further north in sand from the Swan River, which runs through Perth and drains into the same area, reinforcing the age and origin of these ancient materials.

The findings extend to a known area of ​​ancient crust, previously identified in the Narer area of ​​the Murchison region.

One reason it is important to understand the deep crust is that we often find minerals at the boundaries between blocks of this crust. Mapping these blocks can help map out areas to look for mining potential.

Remnants of deep time

So, next time you pick up a rock and rub some mineral grains on your hand, think about how long those grains might have been around.

To understand the time scale, imagine that our planet’s history spanned a year. The Earth formed from swirling dust 12 months ago. Any handful of sand you pick up around Perth will contain one or two grains from about ten months ago. Most of the Australian gold formed seven months ago, and the wild plants arrived just one month ago.

Two weeks ago, dinosaurs appeared. All of humanity has come in the past thirty minutes. And you? On this scale, your life would last about half a second.