It seems that the comets that were pounding the Earth changed the oxygen levels! Remains of ancient asteroids have revealed that the Earth was bombarded by huge space rocks more often than previously thought, greatly altering oxygen levels in the planet's early atmosphere.
When the Earth was formed 4,6 billion years ago, it had almost no atmosphere. As the planet cooled, an atmosphere began to form, although it was primarily made of carbon dioxide and nitrogen in the beginning, which is not as life-friendly as we know it today. Eventually, the Earth experienced a major change in surface chemistry caused by rising oxygen levels, also known as Great Oxidation (GOE).
Between 2,5 and 4 billion years ago, asteroids and comets often fell to Earth. These space rocks (some of which were nearly 10 kilometers wide) greatly influenced the chemistry of the planet's early atmosphere - especially the accumulation of oxygen, according to a new study.
The study found that asteroids and comets fell to Earth more often than previously thought and may have been delayed when oxygen began to accumulate on the planet. Therefore, new models of the atmosphere help scientists to determine when the Earth began to look like the planet it is today.
When an asteroid or comet collides with Earth, it creates a giant cloud of steam. Some of the evaporated rocks in the cloud will condense and solidify, falling back to Earth to form a thin layer of sand-sized particles, also known as impact spheres. Only recently have scientists discovered more of these tiny, ancient particles, which otherwise go unnoticed because they appear to be ordinary pieces of rock.
The researchers analyzed the rock particles to get a better picture of the total number of collision events that occurred in the Earth's chronicle. The new models indicate that the early Earth suffered an impact about every 15 million years, which is about 10 times more common than previously estimated models.
The researchers then modeled how these meteorite impacts would have affected the Earth's atmosphere, revealing that repeated collisions of objects more than 10 km wide would have caused an oxygen sink, which in turn would have sucked in most of the oxygen from the atmosphere.
Their findings are consistent with current geological records which suggest that the early ancient century was characterized by relatively low oxygen levels. Just about 2,4 billion years ago, when the effects slowed, oxygen levels in the Earth's atmosphere rose, paving the way for life as we know it today.
The research is described in document published on Thursday (October 21) in the journal Nature Geoscience.
Source of information: space.com