Periodic Reporting for period 4 - EARTHBLOOM (Earth’s first biological bloom: An integrated field, geochemical, and geobiological examination of the origins of photosynthesis and carbonate production 3 billion years ago)
Période du rapport: 2021-08-01 au 2023-01-31
The ERC Starting Grant Project EARTHBLOOM (2017-2022) aims to better understand the first steps in the evolution of photosynthesis and carbonate mineral production on the early Earth.
The biosphere has been dominated by microbial life for most of Earth’s four and a half billion-year history. Geological records testifying to the presence of microbes on Earth date back to at least three and a half billion years ago. Around three billion years ago, photosynthetic microbes began precipitating large amounts of carbonate minerals, generating entire carbonate platforms similar to the modern day Bahamas. However, instead of coral, these platforms were made of the organo-mineral structures called stromatolites that primitive microbes precipitated as the result of their photosynthetic activity. The capture of atmospheric carbon dioxide, its precipitation into carbonate minerals, and its eventual subduction back into the mantle, is a critical process in the regulation of Earth’s long-term carbon cycle. Understanding how this process began, and what role primitive microbes played in this process, is of paramount importance for understanding how habitable planets establish and maintain a stable and life-sustaining climate state.
Around three billion years ago, photosynthesis was in its infancy. There exist several different kinds of photosynthesis on Earth, but it is overwhelmingly one kind of photosynthesis, so-called oxygenic photosynthesis, that fuels Earth’s modern biosphere. Oxygenic photosynthesis involves the oxidation of water and the release of free oxygen, and this process has played a central role in the evolution of Earth’s surface from oxygen-starved to oxygen-replete conditions over billions of years. However, it is debated when exactly this process began on Earth. The EARTHBLOOM project is focused on a period in time, three billion years ago, when this fundamental metabolism may have first evolved or was in its infancy. Indeed, it may be that the history of carbonate production on Earth is intimately related to evolutionary milestones in the evolution of photosynthesis.
In short, the EARTHBLOOM project seeks to better understand how Earth began making large amounts of carbonate minerals around three billion years ago – and what role Earth’s primitive photosynthetic biosphere played in this important revolution in the chemistry of Earth’s surface.
The biosphere has been dominated by microbial life for most of Earth’s four and a half billion-year history. Geological records testifying to the presence of microbes on Earth date back to at least three and a half billion years ago. Around three billion years ago, photosynthetic microbes began precipitating large amounts of carbonate minerals, generating entire carbonate platforms similar to the modern day Bahamas. However, instead of coral, these platforms were made of the organo-mineral structures called stromatolites that primitive microbes precipitated as the result of their photosynthetic activity. The capture of atmospheric carbon dioxide, its precipitation into carbonate minerals, and its eventual subduction back into the mantle, is a critical process in the regulation of Earth’s long-term carbon cycle. Understanding how this process began, and what role primitive microbes played in this process, is of paramount importance for understanding how habitable planets establish and maintain a stable and life-sustaining climate state.
Around three billion years ago, photosynthesis was in its infancy. There exist several different kinds of photosynthesis on Earth, but it is overwhelmingly one kind of photosynthesis, so-called oxygenic photosynthesis, that fuels Earth’s modern biosphere. Oxygenic photosynthesis involves the oxidation of water and the release of free oxygen, and this process has played a central role in the evolution of Earth’s surface from oxygen-starved to oxygen-replete conditions over billions of years. However, it is debated when exactly this process began on Earth. The EARTHBLOOM project is focused on a period in time, three billion years ago, when this fundamental metabolism may have first evolved or was in its infancy. Indeed, it may be that the history of carbonate production on Earth is intimately related to evolutionary milestones in the evolution of photosynthesis.
In short, the EARTHBLOOM project seeks to better understand how Earth began making large amounts of carbonate minerals around three billion years ago – and what role Earth’s primitive photosynthetic biosphere played in this important revolution in the chemistry of Earth’s surface.
The EARTHBLOOM project focused on three billion year old carbonates that are mostly found in Northern Canada, one of the few places on Earth where rocks of this age are preserved.
The EARTHBLOOM project is using multiple diamond drill cores, donated by a gold mining company, to study the architecture and chemistry of one of Earth’s oldest carbonate platforms, preserved in the Red Lake area, Ontario. These drill cores have now been carefully examined and a detailed stratigraphic log established that describes the nature and thickness of the carbonate rocks and their relationships to other lithologies in the cores. These drill cores have also been extensively sampled and analyzed for chemical signatures that provide insight into carbonate mineral precipitation processes, the chemistry of the seawater in which they were precipitated, in the availability of nutrients in ancient seawater, and whether there was free oxygen being produced at the time of carbonate precipitation. Data from the drill cores has been supplemented with samples obtained from field work in the Red Lake area, where mapping and surface observations provide additional insights into the architecture of this unique deposit. The EARTHBLOOM project examined other sites of similar age in Northwestern Ontario where stromatolitic carbonates are found in abundance, in order to better understand the full extent of carbonate precipitation at this time, and the diversity of habitats and the primitive photosynthetic life that occupied them.
The EARTHBLOOM project has obtained several important results. These include (1) confirmation that Northern Canada really does hold Earth’s most ancient thick occurrences of carbonate minerals, as well as abundant fossilized photosynthetic microbial communities (stromatolites), (2) that these communities were diverse, forming a variety of carbonate structures in a wide range of settings, (3) that abundant associated sulfur minerals were derived from surface reservoirs and show chemical signatures of both atmospheric and biological processing, (4) that chemical records of carbon cycling are rather unusual in these communities, and indicate that some of these microbes may have acquired their carbon using somewhat atypical biological pathways, and (5) that free oxygen was sometimes present in shallow seawater, but was generally scarce. This latter point is especially interesting considering that on the modern Earth, only oxygenic photosynthesis is generally considered an important driver of carbonate mineral precipitation.
The EARTHBLOOM project is using multiple diamond drill cores, donated by a gold mining company, to study the architecture and chemistry of one of Earth’s oldest carbonate platforms, preserved in the Red Lake area, Ontario. These drill cores have now been carefully examined and a detailed stratigraphic log established that describes the nature and thickness of the carbonate rocks and their relationships to other lithologies in the cores. These drill cores have also been extensively sampled and analyzed for chemical signatures that provide insight into carbonate mineral precipitation processes, the chemistry of the seawater in which they were precipitated, in the availability of nutrients in ancient seawater, and whether there was free oxygen being produced at the time of carbonate precipitation. Data from the drill cores has been supplemented with samples obtained from field work in the Red Lake area, where mapping and surface observations provide additional insights into the architecture of this unique deposit. The EARTHBLOOM project examined other sites of similar age in Northwestern Ontario where stromatolitic carbonates are found in abundance, in order to better understand the full extent of carbonate precipitation at this time, and the diversity of habitats and the primitive photosynthetic life that occupied them.
The EARTHBLOOM project has obtained several important results. These include (1) confirmation that Northern Canada really does hold Earth’s most ancient thick occurrences of carbonate minerals, as well as abundant fossilized photosynthetic microbial communities (stromatolites), (2) that these communities were diverse, forming a variety of carbonate structures in a wide range of settings, (3) that abundant associated sulfur minerals were derived from surface reservoirs and show chemical signatures of both atmospheric and biological processing, (4) that chemical records of carbon cycling are rather unusual in these communities, and indicate that some of these microbes may have acquired their carbon using somewhat atypical biological pathways, and (5) that free oxygen was sometimes present in shallow seawater, but was generally scarce. This latter point is especially interesting considering that on the modern Earth, only oxygenic photosynthesis is generally considered an important driver of carbonate mineral precipitation.
Our work on these ancient carbonate platforms has revealed, using stable isotope signatures, that the global carbon cycle must have operated significantly differently in the past, but in a surprising way. While most carbon leaves Earth's surface as marine carbonate sediments, in the deep past it is difficult to account for where all the carbon at Earth's surface was going, if it wasn't in carbonate rocks. Carbon stable isotope signatures provide important clues on ancient carbon cycling as different processes leave different stable isotope imprints on the carbon preserved in carbonate rocks. We found, rather surprisingly, that for the carbonates that we studied to have the stable isotope signatures that we measured, there must have been significant amounts of carbon leaving the Earth system via under appreciated mechanisms that must have very little impact on carbon stable isotope compositions. The best candidate is the uptake of CO2 by the basalts of the ocean floor. These findings open perspectives on how Earth's carbon cycle evolved, and how Earth managed to maintain a stable climate despite important evolution in the Sun's luminosity over billions of years.
Finally, we were able to develop a new radiometric dating technique based on the slow decay of lanthanum into cerium (La-Ce), that allowed us to directly date the ancient production of free oxygen. This is highly important because oxygen-producing photosynthesis is Earth's most important metabolism, whether in terms of total biomass on Earth, or total chemical energy circulating through the biosphere, and it's origin is highly debated, as rock records are often weathered and the origin of oxygen signals dubious. Our team successfully applied La-Ce dating to 2.87 to 2.80 billion year old carbonate rocks, all hosting evidence of photosynthetic microbial activity as well as chemical signals for ancient oxygen, spanning three different study sites across NW Canada. We determined using this exciting new radiometric geochronometer that these ancient signals of free oxygen must be primary signatures that predate oxygenation of Earth's atmosphere by 400 million years. This highly significant result places an important new constraint on when oxygenic photosynthesis evolved on Earth, older than many scientists thought, and helps us understand how and when the Earth and its young microbial biosphere took important steps towards towards making Earth the habitable planet teeming with animal life as we know it today.
Finally, we were able to develop a new radiometric dating technique based on the slow decay of lanthanum into cerium (La-Ce), that allowed us to directly date the ancient production of free oxygen. This is highly important because oxygen-producing photosynthesis is Earth's most important metabolism, whether in terms of total biomass on Earth, or total chemical energy circulating through the biosphere, and it's origin is highly debated, as rock records are often weathered and the origin of oxygen signals dubious. Our team successfully applied La-Ce dating to 2.87 to 2.80 billion year old carbonate rocks, all hosting evidence of photosynthetic microbial activity as well as chemical signals for ancient oxygen, spanning three different study sites across NW Canada. We determined using this exciting new radiometric geochronometer that these ancient signals of free oxygen must be primary signatures that predate oxygenation of Earth's atmosphere by 400 million years. This highly significant result places an important new constraint on when oxygenic photosynthesis evolved on Earth, older than many scientists thought, and helps us understand how and when the Earth and its young microbial biosphere took important steps towards towards making Earth the habitable planet teeming with animal life as we know it today.