Hace unos 2 mil millones de años, un impactador se precipitó hacia la Tierra y se estrelló contra el planeta en un área cercana a la actual Johannesburgo, Sudáfrica. El impactador, probablemente un asteroide, formó lo que hoy es el cráter más grande de nuestro planeta. Los científicos han aceptado ampliamente, basándose en investigaciones anteriores, que la estructura de impacto, conocida como el cráter Vredefort, fue formada por un objeto de unos 15 kilómetros (aproximadamente 9,3 millas) de diámetro que viajaba a una velocidad de 15 kilómetros por segundo.

Pero según una nueva investigación de la Universidad de Rochester, el impactador podría haber sido mucho más grande y habría tenido consecuencias devastadoras en todo el planeta. Esta investigación, publicada en el Journal of Geophysical Research:Planets , proporciona una comprensión más precisa del gran impacto y permitirá a los investigadores simular mejor los eventos de impacto en la Tierra y otros planetas, tanto en el pasado como en el futuro.

"Comprender la estructura de impacto más grande que tenemos en la Tierra es fundamental", dice Natalie Allen, ahora Ph.D. estudiante de la Universidad John Hopkins. Allen es la primera autora del artículo, basado en una investigación que realizó como estudiante en Rochester con Miki Nakajima, profesor asistente de ciencias ambientales y de la Tierra. "Tener acceso a la información proporcionada por una estructura como el cráter Vredefort es una gran oportunidad para probar nuestro modelo y nuestra comprensión de la evidencia geológica para que podamos comprender mejor los impactos en la Tierra y más allá".

Las simulaciones actualizadas sugieren consecuencias 'devastadoras'

En el transcurso de 2 mil millones de años, el cráter Vredefort se ha erosionado. Esto dificulta que los científicos calculen directamente el tamaño del cráter en el momento del impacto original y, por lo tanto, el tamaño y la velocidad del impactador que formó el cráter.

Un objeto de 15 kilómetros de tamaño y que viaja a una velocidad de 15 kilómetros por segundo produciría un cráter de unos 172 kilómetros de diámetro. Sin embargo, esto es mucho más pequeño que las estimaciones actuales para el cráter Vredefort. Estas estimaciones actuales se basan en nueva evidencia geológica y mediciones que estiman que el diámetro original de la estructura habría sido de entre 250 y 280 kilómetros (aproximadamente 155 y 174 millas) durante el momento del impacto.

Allen, Nakajima y sus colegas realizaron simulaciones para igualar el tamaño actualizado del cráter. Their results showed that an impactor would have to be much larger—about 20 to 25 kilometers—and traveling at a velocity of 15 to 20 kilometers per second to explain a crater 250 kilometers in size.

This means the impactor that formed the Vredefort crater would have been larger than the asteroid that killed off the dinosaurs 66 million years ago, forming the Chicxulub crater. That impact had damaging effects globally, including greenhouse heating, widespread forest fires, acid rain, and destruction of the ozone layer, in addition to causing the Cretaceous-Paleogene extinction event that killed the dinosaurs.

If the Vredefort crater was even larger and the impact more energetic than that which formed the Chicxulub crater, the Vredefort impact may have caused even more catastrophic global consequences.

"Unlike the Chicxulub impact, the Vredefort impact did not leave a record of mass extinction or forest fires, given that there were only single-cell lifeforms and no trees existed 2 billion years ago," Nakajima says. "However, the impact would have affected the global climate potentially more extensively than the Chicxulub impact did."

Dust and aerosols from the Vredefort impact would have spread across the planet and blocked sunlight, cooling the Earth's surface, she says. "This could have had a devastating effect on photosynthetic organisms. After the dust and aerosols settled—which could have taken anywhere from hours to a decade—greenhouse gases such as carbon dioxide that were emitted from the impact would have raised the global temperature potentially by several degrees for a long period of time."

A multi-faceted model of Vredefort crater

The simulations also allowed the researchers to study the material ejected by the impact and the distance the material traveled from the crater. They can use this information to determine the geographic locations of land masses billions of years ago. For instance, previous research determined material from the impactor was ejected to present-day Karelia, Russia. Using their model, Allen, Nakajima, and their colleagues found that 2 billion years ago, the distance of the land mass containing Karelia would have been only 2,000 to 2,500 kilometers from the crater in South Africa—much closer than the two areas are today.

"It is incredibly difficult to constrain the location of landmasses long ago," Allen says. "The current best simulations have mapped back about a billion years, and uncertainties grow larger the further back you go. Clarifying evidence such as this ejecta layer mapping may allow researchers to test their models and help complete the view into the past."

Undergraduate research leads to publication

The idea for this paper arose as part of a final for the course Planetary Interiors (now named Physics of Planetary Interiors), taught by Nakajima, which Allen took as a junior.

Allen says the experience of having undergraduate work result in a peer-reviewed journal article was very rewarding and helped her when applying for graduate school.

"When Professor Nakajima approached me and asked if I wanted to work together to turn it into a publishable work, it was really gratifying and validating," Allen says. "I had formulated my own research idea, and it was seen as compelling enough to another scientist that they thought it was worth publishing."

She adds, "This project was way outside of my usual research comfort zone, but I thought it would be a great learning experience and would force me to apply my skills in a new way. It gave me a lot of confidence in my research abilities as I prepared to go to graduate school." + Explora más

More than one asteroid could have spelled doom for the dinosaurs