Between 2.5 and 4 billion years ago, during the Archean eon, Earth’s weather was frequently described as hazy with a probability of asteroid.
Asteroids and comets collided with Earth all the time back then. The biggest ones, which were more than six miles wide, affected the chemistry of the planet’s early atmosphere. While geologists generally believe this, what hasn’t been as well understood is how frequently these massive asteroids would hit and how the aftermath from the collisions affected the atmosphere, notably oxygen levels. A group of researchers now believes they have some of the answers.
In new research, a Harvard professor was part of a team that analyzed remains of ancient asteroids and modeled the effects of their collisions to show that the strikes occurred more frequently than previously thought and may have delayed when oxygen began to accumulate on the planet. The new models will aid scientists in determining when the planet began its journey toward becoming the Earth we know today.
Free oxygen in the atmosphere is vital for every living entity that uses respiration to generate energy. We would most likely not exist if the atmosphere did not accumulate oxygen.
The researchers discovered that existing planetary bombardment models overestimate the frequency with which asteroids and comets will strike Earth. The new, higher collision rate implies that impactors strike the globe around every 15 million years, which is nearly ten times more frequent than existing predictions.
The scientists discovered this after reviewing recordings of what appear to be typical fragments of rock. They impact spherules, which originated in catastrophic crashes when big asteroids or comets collided with the Earth.
As a result, the energy from the collision melted and evaporated the rocky components in the Earth’s crust, propelling them up in a massive plume. Small droplets of molten rock in that cloud would then condense and freeze, falling to Earth as sand-sized particles that would settle back onto the Earth’s crust. These ancient markings are difficult to locate because they create layers in the rock that are generally only an inch or so thick.
Because the impact particles are so little, you simply go on lengthy treks and look at all the rocks you can find. They’re really easy to overlook.
These additional spherule layers boosted the overall number of known impact events during the early Earth’s history. This enabled the Southwest Research Institute team to update their bombardment models and discover that the collision rate had been underestimated.
The researchers then estimated how all of these consequences would have affected the atmosphere. They effectively discovered that the cumulative effects of meteorite hits by objects larger than six miles likely caused an oxygen sink that drew the majority of the oxygen out of the atmosphere.
The findings are consistent with the geological record, which demonstrates that during the early Archean aeon, oxygen levels in the atmosphere fluctuated but remained relatively low. This was true until around 2.4 billion years ago when the bombardment slowed. The Great Oxidation Event, caused by an increase in oxygen levels, caused a profound shift in surface chemistry on Earth.