City-Sized Asteroids Hit the Earth More Frequently than Previously Thought

A new model might provide insight into the role asteroids played in early evolution.
Chris Young

Huge asteroid impacts on Earth may have occurred up to 10 times more frequently than was previously thought, a new analysis conducted by researchers at the US-based Southwest Research Institute reveals.

The analysis shows that asteroids, ranging from city-sized to small province-sized, struck on average every 15 million years between 2.5 and 3.5 billion years ago.

According to a press statement from the Goldschmidt Geochemistry Conference, where the research was presented, the scientists behind the analysis are now delving into the effects the added number of impacts may have had on the Earth's surface chemistry and, subsequently, on the early evolution of life.

For the new analysis, the researchers developed an impact flux model and compared that with a statistical model of ancient spherule layer data, which is widely accepted in the scientific community.

Using that approach, they found that current models of asteroid impacts during the Earth's early formation period drastically underestimate the number of collisions that occurred.

The new data suggests that the Earth was likely being hit by an asteroid the same size as the one that killed off the dinosaurs approximately once every 15 million years.

Early asteroids may have brought life to Earth

The effect of asteroids on Earth's chemistry over billions of years is an area of research that could provide a glimpse as to the origin of life on Earth.

Dr. Simone Marchi, of the Southwest Research Institute, said "one outcome we are looking at is to try to understand if these impacts may have affected the evolution of atmospheric oxygen."

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"We find that oxygen levels would have drastically fluctuated in the period of intense impacts," Marchi continued. "Given the importance of oxygen to the Earth's development, and indeed to the development of life, its possible connection with collisions is intriguing and deserved further investigation. This is the next stage of our work."

Earlier this year, scientists revealed findings from the Japan Aerospace Exploration Agency's (JAXA) Hayabusa-1 mission, which collected a sample from an asteroid in 2010. Their study showed that the most common type of asteroid to come to Earth, S-type asteroids, can contain the raw components essential to life.

Such findings can be applied to the study of the Earth's early years. Though direct evidence of impacts from so far back is very difficult to find, the new analysis nevertheless points to the fact that asteroids had a much larger impact on Earth's early formative years than previously thought.

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