How fluctuating oxygen levels accelerate animal evolution

According to a new study, 1 billion years ago, oxygen levels in Earth's atmosphere were likely to have "fluctuated wildly," creating a possible acceleration of oxygen levels.
Conditions for the development of
early animal life.

Scientists believe that oxygen in the atmosphere develops in three stages, starting with the Great Oxidation Event 2 billion years ago, when oxygen first appeared in the
atmosphere.
The third stage, about 400 million years ago?, was when oxygen in the atmosphere rose to today's levels
.

What is uncertain is what happened in the second phase, in a period known as the Neoproterozoic , which began about 1 billion years ago and lasted about 500 million years, during which early forms of animal life emerged

 
The question scientists are trying to answer is – is there anything unusual about the change in oxygen levels in the Neoproterozoic that may have played a key role in this? In the early days of animals? Evolving – whether oxygen levels rise suddenly or increase gradually

Fossil traces of early animals known as the Ediacaran fauna , multicellular organisms that require oxygen have been found in sedimentary rocks dating from 541 to 635 million years ago

To try to answer this question, a team from the University of Leeds, supported by the University of Lyon, the University of Exeter and University College London, used measurements of different forms of carbon or carbon isotopes found in shallow sea limestone
.
According to? The isotopic ratios of the different types of carbon discovered ?,? researchers able to calculate the levels of photosynthesis that existed millions of years ago and infer the levels of oxygen in the atmosphere

The result of the calculations was that they were able to record the level of oxygen in the atmosphere over the past 1.
5 billion years?, which tells us how much oxygen diffused into the ocean to support early marine life
.

Biogeochemical modeller Dr Alex Krauss, who completed his PhD at the University of Leeds' School of Earth and Environment and was the lead scientist on the project, said the findings shed new light on
how oxygen levels on Earth change.

He added: "The early Earth, for the first 2 billion years of its existence, was hypoxic, with no oxygen
in the atmosphere.
Then the oxygen level begins to rise, which is known as the Great Oxidation Event
.

"Until now, scientists have believed that After the Great Oxidation Event, oxygen levels were either low, and then oxygen levels spiked before we saw the first animals evolve, or they were high
for millions of years before animals appeared.

"But our study shows that oxygen levels vary much
more.
" For a long time before the advent of early animals, oxygen was in the presence of oxygen in the past.
There has been an oscillation
between high and low levels.
? We see that the marine environment where early animals lived was once rich in oxygen, while at other times it was not
.

Dr Benjamin Mills, who leads the Earth Evolution Simulation Group at the University of Leeds and also leads the project, said: "This cyclical change in environmental conditions creates evolutionary pressures, some life forms may have become extinct and new ones may emerge
.
"

Dr Mills said the oxygenated period expanded the so-called "habitable space" — the part of the ocean where oxygen levels were high enough to support early animal life forms

"It has been proposed in ecological theory that when a habitable space is expanding and contracting, this can support rapid changes
in biodiversity," he said.

"When oxygen levels drop, some organisms face severe environmental stress that could lead to extinction
.
As oxygen-rich waters expand, new spaces allow survivors to rise to an ecological advantage
.

"These expanded livable spaces will last for millions of years, giving the ecosystem plenty of time
to grow.
"