Scientists at the University of Southhampton have discovered that changes in Earth’s orbit may have allowed complex life to survive during the most hostile climate episode the planet has ever experienced.
The researchers studied a succession of rocks deposited when most of Earth’s surface was covered in ice during a severe glaciation, named ‘Snowball Earth’, that lasted over 50 million years.
‘One of the most fundamental challenges to the Snowball Earth theory is that life seems to have survived,’ says Dr. Thomas Gernon, co-author of the study. ‘So, either it didn’t happen, or life somehow avoided a bottleneck during the severe glaciation.’
The researchers visited the South Australian outback where they targeted kilometre thick units of glacial rocks formed about 700 million years ago. At that time, Australia was located closer to the Equator. The rocks they studied, however, show irrefutable evidence that ice sheets extended as far as the equator at that time, providing compelling evidence that Earth was completely covered in an icy shell.
During this glaciation, the frozen ocean would have been totally cut off from the atmosphere. Without the normal exchange between the sea and air, many variations in climate that normally occur would not have.
In their study, the team made the discovery that the layered rocks preserve evidence for nearly all orbital cycles. These astronomical cycles change the amount of incoming solar radiation that reaches the Earth’s surface and thus control the climate.
The team’s results help explain the presence of sedimentary rocks of this age that show evidence for flowing water at Earth’s surface. Dr. Gernon states: ‘This observation is important, because complex multicellular life is now known to have originated during this period of climate crisis, but previously we could not explain why’.
https://phys.org/news/2021-07-earth-orbit-enabled-emergence-complex.html