Related Experiment Video
Updated: Jun 28, 2026
09:45
Laboratory Simulation of an Iron(II)-rich Precambrian Marine Upwelling System to Explore the Growth of Photosynthetic Bacteria
Published on: July 24, 2016
Carbon isotopic composition of individual Precambrian microfossils
C H House1, J W Schopf, K D McKeegan
1Department of Earth and Space Sciences, IGPP Center for Astrobiology, University of California, Los Angeles 90095-1567, USA.
Geology
|September 7, 2001
Summary
Ancient microorganisms from Australia and Canada show carbon isotope ratios. These findings suggest carbon fixation primarily occurred through the Calvin cycle or acetyl-CoA pathway, aligning with cyanobacteria.
Area of Science:
- Paleobiology
- Geochemistry
- Isotope Geochemistry
Background:
- Stromatolitic cherts contain fossil microorganisms from ancient Earth.
- Understanding early life's metabolic pathways is crucial for astrobiology and Earth's history.
Purpose of the Study:
- To analyze carbon isotope ratios in microfossils from the Bitter Springs and Gunflint Formations.
- To infer the carbon fixation pathways used by these ancient microorganisms.
Main Methods:
- Ion microprobe analysis of carbon isotope ratios (delta 13C(PDB)) in 30 fossil specimens.
- Morphological analysis to suggest phylogenetic affinities.
Main Results:
- Carbon isotope values for Bitter Springs microfossils ranged from -21.3% to -31.9%.
- Carbon isotope values for Gunflint microfossils ranged from -32.4% to -45.4%.
- Results are consistent with Calvin cycle or acetyl-CoA pathway, but not 3-hydroxypropionate or reductive TCA cycles.
Conclusions:
- The studied microfossils likely utilized the Calvin cycle or acetyl-CoA pathway for carbon fixation.
- Morphological and isotopic data support an affinity to cyanobacteria.
- Excludes the 3-hydroxypropionate and reductive tricarboxylic acid cycles as primary carbon fixation pathways for these organisms.
Related Concept Videos
02:35What is Evolutionary History?
Scientists record evolutionary history by analyzing fossil, morphological, and genetic data. The fossil record documents the history of life on Earth and provides evidence for evolution. However, both fossil and living organisms offer evidence that outlines Earth’s evolutionary history.Phylogenetic trees illustrate the evolutionary relationships among these organisms. Scientists infer organisms’ common ancestry by evaluating shared morphological and genetic characteristics. Together, the fossil...
02:56The Fossil Record
The fossil record documents only a small fraction of all organisms that have ever inhabited Earth. Fossilization is a rare process, and most organisms never become fossils. Moreover, the fossil record only exhibits fossils that have been discovered. Nevertheless, sedimentary rock fossils of long-lived, abundant, hard-bodied organisms dominate the fossil record. These fossils offer valuable information, such as an organism's physical form, behavior, and age. Studying the fossil record helps...
02:48Radioactive Decay and Radiometric Dating
Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. The number of disintegrations per unit time is called the activity (A), which is directly proportional to the number of nuclei in the sample. The decay constant (λ) is an average probability of decay per nucleus in unit time.
01:13Mass Spectrometry: Isotope Effect
Most elements exist in nature as a mixture of isotopes. The isotopes differ in weight due to their respective number of neutrons. The molecular weight of a molecule is different depending on the specific isotope of its elements involved. As a result, the mass spectrum of the molecule exhibits peaks from the same fragment at multiple positions. The positions of these mass signals depend on the mass differences between isotopes. Furthermore, the intensity of these signals is dependent on the...
01:27Diversity of Protists III
Rhizaria are a diverse group of unicellular protists characterized by their threadlike cytoplasmic extensions known as pseudopodia. These structures aid in both locomotion and feeding, giving Rhizaria an amoeboid appearance. Their amoeboid morphology once led to taxonomic confusion, but molecular phylogenetics has clarified their evolutionary placement and emphasized their shared use of pseudopodia despite divergent lineages.This clade comprises diverse lineages such as Chlorarachniophyta,...
01:08Evolution of Microbial Genome
Microbial genome evolution is a highly dynamic process shaped by continual gene gain and loss across species and strains. This genomic flexibility allows microorganisms to adapt rapidly to environmental pressures and interactions with other organisms. Central to understanding this diversity is the distinction between the core and pan genomes.The core genome comprises the genes shared by all sampled strains of a species, representing essential functions needed for fundamental cellular processes.