Nir Galilee / ETH zurique
Cross cut of an egg -shaped iron oxide stone: contains information on the amount of organic carbon present in the sea millions of years, such as a time capsule
A team of researchers was able to measure for the first time how the amount of organic carbon dissolved in the oceans has changed over geological time. The results contradict all allegations previously accepted on the history of Earth’s evolution.
Earth scientists often face huge challenges when studying the history of the planet: many significant events have occurred so long ago that there are Few direct traces available.
Consequently, researchers often have to rely on indirect evidence or computational models to conduct their research.
In a new study, a team led by Jordon Hemingwayteacher at ETH Zurich, has now discovered a unique natural testimony From this period: small iron oxide oval stones that allow to directly measure carbon reserves in the primordial oceans.
At first sight, They look like grains of sandbut in the way they form, these so -called ooides The most moving snowballs are more like layers as they are pushed by the seabed by the waves.
During this process, organic carbon molecules adhere to stones and become part of their crystalline structure.
In analyzing these impurities, Hemingway’s team was able to rebuild the supply of organic carbon in the oceans – up to 1.65 billion years ago.
In yours, recently published in the magazine Naturethe investigators show that, between 1,000 and 541 million years agothis deposit was considerably lower than what was assumed previously.
You are disquinvecyrefutes common explanations for gemical events and significant biological of that time and shed a new light on the history of the earth.
The ocean as a reservoir of the Life Construction Blocks
How does carbon reach the oceans?
On the one hand, carbon dioxide (CO₂) dissolves from air in seawater and is transported to the depths by the mixture processes and ocean currents, where it remains for long periods. On the other hand, organic carbon is produced by photosynthetic organisms such as phytoplankton or certain bacteria.
Using the energy of sunlight and CO₂, these microorganisms produce the compounds of organic carbon. When organisms die, they slowly sink toward the bottom of the sea in the form of “navy snow”.
If it reaches the bottom without being consumed by other organisms, carbon is stored in the sediment Marine for millions of years.
But It is not just phytoplankton that provides carbon. Life construction blocks are also reused: microorganisms decompose excrement and dead organisms, releasing these blocks again.
These molecules form the call dissolved organic carbonwhich circulates freely in the oceans: a huge reservoir which contains 200 times more carbon than the one that is really “incorporated” in marine life.
The oxygen revolution changed everything
Based on anomalies in ocean sedimentary rocks, the investigators assumed that this reservoir of construction blocks would have been particularly bulky between 1,000 and 541 million years ago.
For a long time, this hypothesis served as the basis for explaining how at the same time came the glacial ages and the complex life.
The photosynthetic production of life construction blocks is closely linked to the development of the atmosphere and the most complex life forms. It was just through photosynthesis that oxygen began to accumulate in the atmosphere.
In two waves, known as Oxygen catastrophesthe oxygen content increased to the current level of 21%. Both events were accompanied by extreme glacial ages that covered the planet with ice.
However, Life continued to experience new strategies: During the first catastrophe of oxygen, between 2.4 and 2.1 billion years ago, organisms developed a metabolism capable of converting energy food with the help of oxygen. This extremely efficient form of generating energy has enabled the development of more complex life forms.
Carbon content much lower than the assumed
To manage these links between gemical and biological developments, Hemingway’s team has developed a new method that allows directly determining the size of the marine reservoir of life building blocks at that time, based on the carbon particles present in the Ooids.
“Our results contradict all previous assumptions”Summaries Hemingway, in an ethi zurich.
According to the study results, between 1,000 and 541 million years ago, the oceans contained no longer, but in reality 90 to 99% less carbon dissolved organic than today. Only after the second oxygen catastrophe did the values reach the current level of 660 billion tons of carbon.
“We need new explanations about how glacial ages, complex life and increased oxygen are related, ”says the main author of the study, Nir greedwhich explains the enormous reduction of the carbon reservoir with the appearance of larger organisms at the time: unicellular and primitive multicellular organisms They sank faster after deaththus increasing the “marine snow”.
However, Carbon particles were not recycled in the deepest layers of the ocean due to the scarcity of oxygen; They settled under the sea, causing the dissolved organic carbon reservoir to decrease dramatically. Only when oxygen accumulated In the depths, the reservoir grew again to the current volume.
Of the primordial ocean to the present day
Although the periods studied already belong to the remote past, the conclusions of the investigation They are significant for the future: They change our view of how life on earth, and possibly also in other exoplanets, developed.
At the same time, they help us understand how the earth reacts to disturbances, Humans being one of those disturbances: Heating and pollution of oceans caused by human activity are currently reducing marine oxygen levels.
Consequently, it cannot be excluded that events similar to those described can repeat in a distant future.
