Meteorite impact one billion years ago may have changed the evolution of life on Earth

A new study pushes the date of a Scottish meteorite impact from the often cited 1.2 billion years to about 990 million years. That single change reshapes a key chapter in Earth history and reframes when complex life began to spread beyond the oceans.

The evidence sits inside a rugged slice of rock in northwest Scotland called the Stac Fada Member. Hidden within it are tiny timekeepers that can lock in the story of an impact with remarkable precision.

Why this Scottish impact matters

This project was led by Chris Kirkland of Curtin University, with collaborators across several institutions including NASA’s Johnson Space Center (JSC). The team combined field observations with high precision lab work to build a coherent timeline.

“These microscopic crystals recorded the exact moment of impact, with some even transforming into an incredibly rare mineral called reidite,” said Prof. Kirkland.

That physical record allows researchers to move beyond guesswork and anchor the event in time.

Most known terrestrial impact craters still lack precise ages, which limits what we can test about life and climate. A 2022 review tallied 188 craters worldwide and found only 37 had precise dates.

This work adds one more firm timestamp to that sparse calendar. It also links the impact horizon to a period when life was changing fast on land.

Rocks recorded the Scottish impact

The key witness is zircon, a hard mineral that resists heat, erosion, and chemical attack. Zircon crystals can trap uranium atoms when they form and later show how much of that uranium decayed to lead, which is the basis of the clock.

Another clue is reidite, a high pressure version of zircon that forms only during intense shocks.

Prior work on the same Scottish unit reported reidite preserved as narrow lamellae in shocked zircon, confirming extreme pressures consistent with an impact.

The Stac Fada Member is an ejecta deposit, a mix of shattered rock, spherules, and altered melt that fell back to Earth after the blast.

Its texture shows reworking by water and gravity, which complicates dating but also preserves a rich record of what happened next.

The zircon clock runs on U-Pb dating, which reads the ratios of uranium to lead isotopes. Shock can partially reset that clock, but careful modeling can back out the timing of the disturbance.

Dating the rocks

The researchers targeted shocked zircon and its recrystallized zones, which formed during post shock heating. Those zones hold the cleanest record of when the clock last reset.

They then compared disturbed and undisturbed zircon populations from layers above and below the ejecta. That side by side approach tested whether the reset signal was unique to the ejecta, not a later overprint.

“When a meteorite hits, it partially resets the atomic clocks inside the zircon crystals,” said Prof. Kirkland. The team used that partial reset to isolate the moment of impact and recover a precise date.

The result moves the Stac Fada event into the early Neoproterozoic. That is a time marked by changing continents, evolving atmospheres, and a push by complex cells into new habitats.

What the new age changes

An earlier dating of minerals lining degassing cavities in the same unit yielded 1,177 million years, which became the common reference.

The new zircon based work points to a later episode, and it explains why that older method may have sampled detrital or altered minerals rather than true impact products.

The timing now lines up with evidence for early freshwater eukaryotes in nearby rocks. Those are complex cells, the group that includes plants, animals, and fungi, showing a foothold outside the sea around one billion years ago.

This overlap does not claim cause and effect. It does open testable questions about how impacts may have stirred lakes, soils, and air in ways that mattered to early ecosystems.

No one has pinned down the crater that produced the Stac Fada ejecta. The deposit shows clear impact fingerprints, yet the source structure remains elusive.

Geophysical surveys, refined mapping, and careful sampling may narrow the search. The new date guides where to look by constraining which rocks are even candidates.

Why this matters beyond Scotland

Better dates let scientists compare impacts to biological and environmental events without hand waving. With a secure age, we can check whether shifts in sediments, chemistry, or fossils cluster around impact horizons.

This is especially important for the rise of complex life on land. Independent fossil evidence shows freshwater and marginal terrestrial habitats hosted diverse eukaryotes by about one billion years ago, and that context now matches the Scottish impact window.

Tracking impact timing also helps calibrate how Earth processes recover after large disturbances. That matters for everything from climate models to the long view of planetary habitability.

Teams can revisit nearby fossil bearing rocks and ask sharper questions about community structure, nutrients, and environmental stress. Lab groups can test how shock and heat alter zircon in controlled ways to refine the methods.

The hunt for the crater will continue with better tools and a tighter clock. Each new constraint adds clarity to a once blurry slice of deep time.

The study is published in Geology.

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