The ‘oldest’ impact crater of the earth is much younger than before, new study finds

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This article was originally published on The conversation. The publication has contributed the article to Space.com’s Expert Voices: Op-Ed & Insights.

Have you ever been late because you read a clock wrong? Sometimes the “clocks” geologists that are used so far can also be read incorrectly. Unraveling the 4.5 billion years of history of the earth with rocks is difficult things.

An example: The discovery of an old meteorite impact crater was recently reported in the remote Pilbara region in West -Australia. The original study achieved the headlines by another group with the claim that the crater formed 3.5 billion years ago. If it is true, it would be by far the oldest of the earth.

It appears that we have also investigated the same site. Our results are published today in a science prospect. Although we agree that this is the location of an old meteorite impact, we have drawn various conclusions about age, size and meaning.

Let’s look at the claims about this fascinating crater.

One impact crater, two versions of events

Planetary scientists are looking for old effects to learn about the early formation of the earth. Until now, nobody has found an impact crater that is older than the 2.23 billion-year-old Yarrabubba structure, also in Australia. (Some authors from both 2025 Pilbara studies were co -authors during the 2020 Yarrabubba study.)

The new competition is in an area called North Pole Dome. Despite the name, this is not where Santa lives. It is a dry, hot, ochre-fitted landscape.

The first report on the new crater claimed that it was formed 3.5 billion years ago and had more than 100 kilometers of diameter. It was proposed that such a big impact could have played a role in forming continental crust in the Pilbara. More speculatively, the researchers also suggested that it may have influenced early life.

Our study concludes that the impact actually happened much later, somewhere after 2.7 billion years ago. This is at least 800 million years younger than the earlier estimate (and we think it is probably even younger; more about that in an instant).

We also determined that the crater was much smaller – about 16 km in diameter. In our opinion, this impact was too young and too small to have influenced the formation of the continent or early life.

So how can two studies come to such different findings?

Subtle indications of an impact

The originally circular crater is deeply eroded, so that only subtle instructions on the landscape are left behind. Under the rust -colored basalt, however, there are unique meaningful signs of meteorite impact: smells of cones.

Spread cones are distinctive fossilized prints of shock waves that have gone through rocks. Their unique conical forms form under short but immense pressure where a meteorite strikes the earth.

Both studies found shattered cones and agree that the site is an old impact.

This new crater also needed a name. We consulted the local Aboriginals, the Nyamal, who shared the traditional name for this place and his people: Miralga. The name “Miralga Impact Structure” recognizes this heritage.

Determining the timing of the impact

The impacting age was estimated by field observations, because neither studies found material that probably resulted in an impact -age due to radiometric dating – a method that uses measurements of radioactive isotopes.

Both studies apply a geological principle that is called the law of superposition. This states that in the course of time the one is deposited one on top of another, so rocks on top are younger than those below.

The first group found shattered cones in and under a sedimentary layer that is known to have been deposited 3.47 billion years ago, but no shattered cones in younger rocks above this layer. This meant that the impact took place during the deposition of the sedimentary layer.

Their observation seemed to be a “smoking gun” for an impact 3.47 billion years ago.

It turned out that the story was more.

Our research found shattered cones in the same 3.47 billion -year -old rocks, but also in younger parent rocks, including lavas that were known to broke out 2.77 billion years ago.

The impact had to occur after the formation of the youngest rocks that contain shattered cones, which means that somewhere after the 2.77 billion year old lava’s.

At the moment we don’t know exactly how young the crater is. We can only limit the impact that took place between 2.7 billion and 400 million years ago. We are working on dating the impact through isotopic methods, but these results are not yet there.

Smaller than originally thought

We made the first card that showed where shattered cones are found. There are many hundreds over an area of 6 km wide. We calculate from this map and their orientations that the original crater had a diameter of approximately 16 km.

A 16 km crater is far away from the original estimate of more than 100 km. It is too small to have influenced the formation of continents or life. By the time of the impact, the Pilbara was already quite old.

A new connection with Mars

Science is a self -asking sport. Claims of discovery are currently based on data available, but they often require adjustment based on new data or observations.

Although it is not the oldest in the world, the Miralga impact is scientifically unique, because craters are formed in basalt rare. Most basalt there formed 3.47 billion years ago, making them known for the oldest shocked target rocks.

Prior to the impact, this old basalt were chemically changed by seawater. Sedimentary rocks in the neighborhood also contain the earliest established fossils on earth. Such rocks probably covered much of the early earth and mars.

This makes the Miralga impact structure a playground for planetary scientists who study the cratered surface (and perhaps early life) of Mars. It is an easily accessible evidence for Mars exploratory instruments and images, here on earth.

This article has been re -published from The conversation Under a Creative Commons license. Read the Original article.