|Glacial meltwater was a “crucial lifeline” to aerobic marine habitats during the ice age. / Photo by Christian via 123rf|
A world without liquid water and just pure solid ice in almost all directions would certainly not be a place in which life forms can survive. Yet, our planet has endured several frozen periods. How then did the early animals possibly survive during such a period? The answer is glacial meltwater, according to McGill University-led research.
Their recent study finds that glacial meltwater was a “crucial lifeline” to aerobic marine habitats during the ice age.
Understanding Snowball Earth
The Earth has experienced several changes in its 4.5-billion-year history. One dramatic episode occurred between 700 million and 600 million years ago, which geologists have called the Snowball Earth. This hypothesis suggests that the Earth’s land surfaces and oceans from the poles to the equator were once covered by ice.
When icy deserts dominated the Earth
It is one of the “Earth’s most severe ice ages,” according to McGill University’s postdoctoral researcher in the Department of Earth and Planetary Sciences Maxwell A. Lechte and team. They explained that the widespread ice coverage happened during the Cryogenian Period. Scientists have been puzzled for many years by how early life survived during such a period where oceans were not receiving life-giving oxygen.
Lechte and colleagues used the iron-rich rocks that were left behind by glacial deposits in California, Namibia, and Australia to better understand the environmental conditions during the severe ice age period. To obtain these rock formations, the team utilized the geological clues and maps from the locals and hiked the rocky outcrops where the rocks can be found. They then examined the chemistry of iron formations of the said naturally occurring solid mass and it led them to estimate the oxygen in the oceans when Snowball Earth glaciations happened. Their findings also helped them better understand the effects of lack of oxygen on all marine life that are oxygen-dependent. Some earliest animals that are oxygen-dependent are the sea sponges.
|Tthe widespread ice coverage happened during the Cryogenian Period. / Photo by Evgenii Krasnikov via 123rf|
Supply of oxygenated meltwater
The researchers suggest that although icy deserts dominated the Earth during the Cryogenian period and that the oceans would be uninhabitable to aerobic marine habitats because of lack of oxygen, there was a “critical supply of oxygenated meltwater.” Their study appeared in science news platform Science Daily. The supply of oxygenated meltwater was found in areas where the grounded ice started to float or what is now referred to as the glacial oxygen pump.
This means that air bubbles were trapped in the glacial ice and were released into the water as it melted This helps the animal life survive in extreme glaciation.
The lead author added that since global freeze happened before the evolution of complex animals evidenced a connection between animal evolution and Snowball Earth. The team theorized that the harsh environment conditions stimulated the animals’ diversification into more complex forms.
Lechte added that although their study focused more on the availability of oxygen during the Cryogenian period, the primitive eukaryotes (organisms) would have likewise needed food to survive. This is why further study of the early food web is needed. The iron could be a clue to how the eukaryotic life lived in the glacial waters as the seawater was a source of dissolved iron.
Today, chemotrophic bacteria take their energy from the oxidation of dissolved iron. Chemotrophs are a class of organisms that collect their energy through the oxidation of inorganic molecules, such as magnesium and iron. The starting point of such a food web can also be referenced to how modern ice environments now host complex ecosystems.
The researchers believe that their findings solved two mysteries about the Cryogenian period’s Snowball Earth. First, it explains how early animals lived during global glaciation and second, it details the “return of geological record after an absence of over a billion years,” Professor Galen Halverson said.
What prevented the Earth’s full freeze-over?
Geologist Linda Sohl of the NASA Goddard Institute for Space Studies, who is not involved in the McGill University-led research, previously conducted a study about Snowball Earth together with her colleagues. During their simulations of the Cryogenian period, they discovered that the planet’s global mean temperature could have fallen 12 degrees Celsius below freezing but not completely frozen over. Their findings led to the prediction that some parts of the oceans remain ice-free.
“The ocean circulation seems to help in preventing a full freeze-over,” Sohl said. They said that there is open water in the tropics although glaciers are covering much of the landmass.
Meanwhile, the National Show and Ice Data Center, an information and referral center in the US in support of polar and cryospheric research, shared that there are animals that have adapted to co-exist with the cold. These animals include bison, elk, deer, and other grazing animals that use their muscles and hooves to clear the snow away from plants to survive. There are also other animals, such as the snowshoe hare, that develop ways to travel on top of deep snow. For example, they spread their toes to walk without falling through.