Scientists know that the Earth was bombarded by huge percussionists in the distant past, but a new analysis suggests that the number of these impacts may have been 10 times higher than previously thought. This translates into a collision barrier similar to the scale of the asteroid strike that wiped out the dinosaurs on average every 15 million years between 2.5 and 3.5 billion years ago. Some of these individual influences may have been much larger, possibly ranging from city size to small province size. Scientists are also considering the effect the effects may have had on Earth’s evolving near-surface chemistry. This work will be presented at the Goldschmidt Geochemistry Conference.
The Earth’s early years were unbelievably violent compared to today. Scientists believe that the Earth was hit by a significant number of large asteroids (larger than 10 km in diameter), and this would have had a significant effect on the Earth’s chemical surface near the surface and the ability to support life. The impact of just such a collision was shown relatively recently by the Chicxulub impact 66 million years ago, leading to the extinction of dinosaurs. However, the early Earth was very different from the Earth at the time of the Chicxulub impact, and so were the effects of collisions.
Impact craters from similar collisions can be seen on the Moon and other rocky planets, but atmospheric weathering and plate tectonics tend to obscure direct evidence of ancient impact craters on Earth. However, echoes of these distant influences can be seen in the presence of “spheres” found in ancient rocks; the large impacts threw up molten particles and vapors, which then cooled and fell to the ground to be embedded in rocks as small spherical glassy particles. The greater the impact, the more these particles would have spread from the impact site, so global distribution of a thick layer of spheres shows a huge impact.
Researcher Dr. Simone Marchi of the Southwest Research Institute (Boulder, CO, USA) said:
“We have developed a new power flux model and compared it with a statistical analysis of old ball layer data. With this approach, we found that current models of Earth’s early bombardment seriously underestimate the number of known impacts as recorded by spherical layers. The true current of power could have been up to a factor of 10 times higher than previously assumed in the period between 3.5 and 2.5 billion years ago. This means that in the early period we were probably hit by a Chicxulub effect on average every 15 million years. Some acting! ”
“When we deepen our understanding of the early earth, we find that cosmic collisions are like the proverbial elephant in space. They are often neglected as we lack a detailed knowledge of their number and size, but it is likely that these energetic events fundamentally altered the Earth’s surface and atmospheric evolution. ”
For example, one result we are looking at is trying to understand whether these influences may have influenced the evolution of atmospheric oxygen. We find that oxygen levels would have fluctuated drastically during the period of intense influences. Given the importance of oxygen for the evolution of the Earth and indeed for the evolution of life, its possible connection with collisions is intriguing and deserves further study. This is the next phase of our work. ”
Dr. Rosalie Tostevin from the University of Cape Town said:
“These major impacts would certainly have caused some disruption. Unfortunately, few rocks survive so far back in time, so direct evidence of impacts and their ecological consequences is uneven. The model presented by Dr. Marchi helps us get a better sense of the number and size of collisions on the early earth. “
Some chemical markers suggest that there were “whistles” of oxygen in the early atmosphere before a permanent increase about 2.5 billion years ago. But there is considerable debate about the meaning of these “whiffs” or whether they took place at all. We tend to focus on the Earth’s interior and the evolution of life as a control over the Earth’s oxygen balance, but bombardment with rocks from space provides an exciting alternative. ”
This is an independent comment, Dr. Toast wine was not involved in this work.