Worlds In Collision: Interview With Simone Marchi (Planetary Science)

There are impacts that have marked the architecture of the Solar System, such as the one from which the Moon took shape. Catastrophic impacts, at the origin of great extinctions but also of crucial changes for the evolution of life on Earth. Impacts with objects of at least 10 km in diameter. The book “Colliding Worlds” by the astrophysicist of the Southwest Research Institute of Boulder (in Colorado, USA) Simone Marchi talks about it

Source of inspiration for many successful disaster movies , constant presence – together with pandemics, climate change and nuclear conflicts – in the top ten on the main threats to the future of humanity, the impacts with large asteroids and comets have heavily influenced the architecture of the Solar System and punctuated the history of life on Earth. And it is precisely to the great impacts that have occurred since the early stages of the formation of the solar system that Colliding Worlds is dedicated , a book just published with the Oxford University Press by astrophysicist Simone Marchi .

Originally from Lucca, with a degree and doctorate in Pisa, Marchi is now a researcher at the Space Science and Engineering Division of the Southwest Research Institute in Boulder (Colorado), in the United States. This week he is among the participants in the Goldschmidt Geochemistry Conference – the annual appointment of the European Association of Geochemistry and the Geochemical Society which is taking place these days, from 4 to 9 July – where he was invited as a keynote speaker to present the results of his studies. on the role of the great cosmic collisions in the development of life on Earth. We interviewed him.

Dr. Marchi, the asteroids and in general the wandering rocky bodies you deal with are not pebbles … What is the minimum size they must have to be within your field of investigation? 

“At least 10 km in diameter! Not that there is anything special about this dimension, but it is an affordable value because the effects of such an impact on Earth are believed to be global. Furthermore, this is the estimated size for the asteroid that wiped out the dinosaurs and most (75 percent) of living species 66 million years ago.

Huge objects, then. Here on Earth, fortunately, these big ones seem to rarely arrive today. In the past, however, this was not the case. Why?

“The Earth was formed through the accumulation of a myriad of smaller objects, called planetesimals. These planetesimals continued to collide with Earth for hundreds of millions of years before they were dispersed and removed from the Solar System. Today’s asteroids are what remains – about one in ten thousand – of this vast primeval population of planetesimals. The number of impacts is proportional to the number of objects wandering near the Earth, so the primordial bombardment was much more intense than the current one ».

The subtitle of his book is: How Cosmic Encounters Shaped Planets and Life . Here, what were the main effects of these bombardments, once so frequent, for the formation of our planet and for the evolution of life?

“The primordial bombing has drastically altered the evolution of the Earth. For example, the Moon was formed through a colossal collision that would have melted much of the Earth’s mantle and crust. A new Earth emerged from this catastrophe. Smaller and more frequent impacts would then have altered the chemical composition of the atmosphere, and stimulated the synthesis of organic molecules. Part of the crust would periodically melt, followed by the release of carbon dioxide. The oceans would vaporize repeatedly. The energy of the impacts would have generated hydrothermal systems (like Yellowstone to understand) that extended for thousands of kilometers.

All of this lasted for at least a billion years, before planetesimals were gradually removed and collisions became rare. And similar events have also influenced the evolution of other rocky planets, such as Mars, and asteroids ».

Among all the catastrophic impacts, which one in your opinion has influenced our history the most?

«Undoubtedly the one that generated the Moon. Not only was this collision one of the most energetic, but the presence of the Moon has a positive effect for the Earth: for example, it stabilizes the oscillations of the inclination of its axis. Allowing the Earth to have a stable climate, with the usual alternation of the seasons ».

And what fascinates you most?

Collisions are not only negative for the evolution of life. Indeed, it is the opposite: the surface of the primordial Earth lacked key ingredients for the development of life, and therefore the impacts could contribute to enrich its composition. These are the impacts that interest me most. Think, for example, of a collision with a planetesize of 100 km: today it would be devastating, but in the past it would have deposited important elements – such as carbon, sulfur, nitrogen and phosphorus – which are necessary for life, and would have stimulated the hydrothermal evolution, including the formation of organic compounds, in a region as large as a continent ».

Returning to the wandering rocks: there is an asteroid that bears his name, 72543 Simonemarchi. Can we rest assured? Isn’t it that to promote your book you send him here on tour to visit us?

“He gave me a great advertising idea for the next book! Seriously, 72543 Simonemarchi is located in the main asteroid belt between Mars and Jupiter, and does not seem to have any intention of reaching Earth, at least for the moment ».

We said before that asteroids are never lacking, however, in the top ten of possible causes of extinction. But I’m always in good company. In your opinion, what is most likely to put an end to our species’ adventure on planet Earth?

“Alas, I fear that human stupidity is the number one danger to our species.”

Watch the book trailer of Simone Marchi’s book Colliding Worlds on YouTube :

Featured image: Simone Marchi with his book “Colliding Worlds. How Cosmic Encounters Shaped Planets and Life ”, Oxford University Press, June 2021, 224 pages, 24 euros. Credits for the photo: Maku

Provided by INAF

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