A team from Harvard University presented a study this month that remnants from an ancient Earth exists, right now, inside contemporary Earth. The group believes that their comparisons of isotopic ratios of noble gases from materials deep inside Earth with those near the surface provide testimony that the deep-down material is actually from the Earth that existed before its massive collision with another planet. That immense impact – the largest in geologic history – is what many believe led to creation of the Moon.
The currently favored theory about how the Moon originated says that it was formed 4.5 billion years ago when Earth collided with something enormous. However, this theory also states that the heat generated by such a collision would have been so great as to melt the entirety of Earth, even before some of the debris had a chance to spin off to create the Moon.
Such an impact and its related energy would have been enormous and Sujoy Mukhopadhyay, a Harvard associate professor and leader of the research team, says the the energy released would have been enough to turn the whole planet to liquid. Critically, however, he went on to say that such energy was not distributed evenly throughout the ancient pre-Earth planet. A major portion of the hemisphere that took the impact “would probably have been completely vaporized,” he said, but the other hemisphere would have been somehow shielded and thus “not have undergone complete melting.”
Mukhopadhyay and his group presented their work at the Goldschmidt geochemistry conference in Sacramento, California. Conference organizers describe the gathering as “the prime forum for all recent developments in Geochemistry and related fields.” It was there that the team announced it had uncovered evidence not only that much of Earth had indeed melted as a result of the collision but also that an even more ancient Earth still exists within the mantle of contemporary Earth.
The team recognized that the differences between the isotope ratios in different areas of the Earth required explanation. According to the study, remnants of the ancient Earth that existed before the current still survive. This implies that, despite the incredible drama of the impact event, a thorough mixing of the mantle’s magma did not occur. The idea that such a cataclysmic event did not completely homogenize Planet Earth challenges some of the assumptions about Earth’s formation, as well as the dynamics of such gargantuan impacts. Mukhopadhyay says that if the theory is correct, “then we may be seeing echoes of the ancient Earth, from a time before the collision.”
Richard Carlson, a past president of the conference’s organizer, the Geochemical Society, characterizes the findings of the study as “exciting.” He notes that it builds on existing evidence that some major parts of Earth’s composition were created out of extreme violence. The study provides “a new look at the physical processes by which this can occur.”
The team from Harvard compared noble gas isotope ratios from Earth’s mantle to ratios closer to Earth’s surface. Specific findings showed that the 3He to 22Ne ratio from above is much higher than the same ratio from obtained from deep-mantle samples. An additional ratio, 129-Xenon to 120-Xenon, provided further confirmation when, once again, measurements showed lower ratios from deep inside Earth than those found near its surface. The 129-Xenon that came from the ancient Earth section informed the scientists that the remnant material had been formed before the current Earth, as early as the first 100 million years of the planet’s history.
By Gregory Baskin