Name: how photosynthesis changed earth
Uploaded: 2026-03-12T13:57:27.000Z
Duration: 1 min 26 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Environmental Science

Earth's Systems

9-12.EVS.3.4

Origin of Photosynthesis

La photosynthèse, le processus par lequel les organismes photosynthétiques convertissent l’énergie lumineuse en énergie chimique, a probablement commencé il y a environ 3,5 milliards d’années.La forme la plus ancienne de photosynthèse était probablement anoxygénée, utilisant plusieurs donneurs alternatifs d’électrons, tels que le sulfure d’hydrogène ou le fer ferreux, et libérant du soufre ou du fer oxydé plutôt que de l’oxygène.Par la suite, les cyanobactéries ont développé la capacité de réaliser la photosynthèse oxygénique en utilisant l’eau comme donneur d’électrons et en libérant de l’oxygène comme sous-produit.L’oxygène libéré par les cyanobactéries a réagi avec le fer dissous dans les océans, formant des oxydes de fer insolubles qui se sont déposés sous forme de formations de fer bandés sur le fond marin.Pendant ce temps, les cyanobactéries ont formé des tapis microbiens stratifiés, qui se sont finalement fossilisés en stromatolites.À mesure que la plupart du fer dissous de l’océan s’oxydait et que les principaux puits d’oxygène devenaient de plus en plus saturés, l’oxygène libre a finalement pu s’accumuler dans l’atmosphère.Cette hausse de l’oxygène atmosphérique a déclenché le Grand Événement d’Oxydation il y a environ 2,4 milliards d’années, permettant le métabolisme aérobie et la formation de couches d’ozone.

origine de la photosynthèse

La photosynthèse représente un processus biologique fondamental qui a transformé l’atmosphère terrestre et ouvert la voie à une vie complexe. Apparus il y a environ 3,4 à 3,8 milliards d’années, les premiers organismes photosynthétiques ont exploité l’énergie lumineuse pour produire des composés organiques. Ces phototrophes anoxygénés utilisaient des donneurs d’électrons comme le sulfure d’hydrogène (H₂S) ou le fer ferreux (Fe²⁺), plutôt que de l’eau, et ne libéraient pas d’oxygène moléculaire (O₂) comme sous-produit. Divers groupes, dont le soufre vert et les bactéries pourpres, ont contribué à cette diversité phototrophe précoce.Une étape évolutive importante fut le développement de la photosynthèse oxygénique par les cyanobactéries. Ces micro-organismes utilisaient l’eau comme donneur d’électrons, produisant de l’oxygène moléculaire comme sous-produit. Les cyanobactéries colonisaient des milieux marins peu profonds, formant de nombreux tapis microbiens. Au fil du temps, ces tapis ont accumulé des sédiments et des précipités, se fossilisant en stromatolites — certaines des plus anciennes preuves connues de vie. À mesure que les niveaux d’oxygène augmentaient localement, il réagissait avec une abondance de fer dissous dans l’eau de mer, précipitant sous forme d’oxydes de fer. Ces oxydes se sont déposés sur le fond marin, générant des formations de fer à bandes (FIR), qui servent de marqueurs géologiques clés des premiers changements atmosphériques.Une fois la majeure partie du fer océanique oxydée, l’excès d’oxygène a commencé à diffuser dans l’atmosphère, déclenchant le Grand Événement d’Oxydation (GOE) il y a environ 2,4 milliards d’années. Cette transition a radicalement modifié la chimie et la biologie de la Terre. L’augmentation de l’oxygène atmosphérique a permis l’évolution de la respiration aérobie, qui fournit bien plus d’énergie que le métabolisme anaérobie. Cela a également conduit à la formation de la couche d’ozone stratosphérique (O₃), protégeant la planète des rayonnements ultraviolets nocifs et ouvrant la voie à l’expansion de la vie vers la terre ferme.Bien que le GOE ait favorisé l’innovation évolutive, il a également introduit un stress oxydatif et provoqué l’extinction de nombreux organismes anaérobies. Néanmoins, l’avènement de la photosynthèse oxygénique reste l’un des développements évolutifs les plus significatifs de l’histoire de la Terre.

Origine de la photosynthèse

Photosynthesis represents a fundamental biological process that transformed Earth's atmosphere and paved the way for complex life. Emerging roughly ...

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Education

Enseignement

JoVE Core

Microbiology

Microbiologie

Unit

Unité

Microbial Evolution

Évolution microbienne

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

how photosynthesis changed earth

Photosynthesis changed Earth’s atmosphere and made complex life possible. It began about 3.4 to 3.8 billion years ago, when the first photosynthetic organisms used light energy to build organic compounds. These early organisms were anoxygenic phototrophs, which means they made food from light but did not release oxygen.

Early photosynthesis used hydrogen sulfide (H2S) or ferrous iron (Fe2+) as electron donors instead of water. Because of that, it did not produce molecular oxygen (O2) as a waste product. Green sulfur bacteria and purple bacteria were among the groups that helped shape this early phototrophic diversity.

A major turning point came with cyanobacteria and oxygenic photosynthesis. Cyanobacteria used water as the electron donor and released oxygen. They lived in shallow marine environments and formed large microbial mats. Over time, those mats trapped sediments and precipitates and later became stromatolites, which are some of the oldest evidence of life.

As oxygen built up in local waters, it reacted with dissolved iron in the sea. This formed iron oxides that sank to the seafloor and created banded iron formations, or BIFs. These rocks are important markers of early changes in Earth’s atmosphere and oceans.

After most of the iron in the oceans had been oxidized, oxygen began to enter the atmosphere. This led to the Great Oxidation Event, or GOE, around 2.4 billion years ago. The rise in oxygen changed Earth’s chemistry and biology in major ways.

More oxygen allowed aerobic respiration, which releases much more energy than anaerobic metabolism. It also helped form the stratospheric ozone (O3) layer, which protects life from harmful ultraviolet radiation. That protection helped set the stage for life to spread onto land.

The Great Oxidation Event also had harmful effects. Oxygen created oxidative stress and caused many anaerobic organisms to die out. Even so, the rise of oxygenic photosynthesis remains one of the most important events in Earth’s history.

How Photosynthesis Changed Earth

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key terms and concepts

Explore how early photosynthesis, cyanobacteria, stromatolites, and the Great Oxidation Event transformed Earth’s atmosphere and enabled complex life.

How Photosynthesis Changed Earth | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

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9-12.EVS.3.5

How Photosynthesis Changed Earth

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