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 fotosintesi, il processo attraverso cui gli organismi fotosintetici convertono l'energia luminosa in energia chimica, probabilmente è iniziata circa 3,5 miliardi di anni fa.La forma più antica di fotosintesi era probabilmente anossigenica, utilizzando diversi donatori alternativi di elettroni, come idrogeno solforato o ferro ferroso, e rilasciando zolfo o ferro ossidato invece che ossigeno.Successivamente, i cianobatteri hanno sviluppato la capacità di eseguire la fotosintesi ossigenotica usando l'acqua come donatore di elettroni e rilasciando ossigeno come sottoprodotto.L'ossigeno rilasciato dai cianobatteri reagì con il ferro disciolto negli oceani, formando ossidi di ferro insolubili che si depositarono come formazioni di ferro a bande sul fondale marino.Nel frattempo, i cianobatteri formarono tappeti microbici stratificati, che alla fine si fossilizzarono in stromatoliti.Man mano che la maggior parte del ferro disciolto dell'oceano si ossidava e i principali pozzi di ossigeno negli oceani diventavano sempre più saturi, l'ossigeno libero riuscì infine ad accumularsi nell'atmosfera.Questo aumento dell'ossigeno atmosferico ha innescato il Grande Evento di Ossidazione circa 2,4 miliardi di anni fa, permettendo il metabolismo aerobico e la formazione dello strato di ozono.

origine della fotosintesi

La fotosintesi rappresenta un processo biologico fondamentale che ha trasformato l'atmosfera terrestre e aperto la strada a una vita complessa. Emersi circa 3,4–3,8 miliardi di anni fa, i primi organismi fotosintetici sfruttarono l'energia luminosa per produrre composti organici. Questi fototrofi anossigenici utilizzavano donatori di elettroni come solfuro di idrogeno (H₂S) o ferro ferroso (Fe²⁺), invece dell'acqua, e non rilasciavano ossigeno molecolare (O₂) come sottoprodotto. Vari gruppi, tra cui lo zolfo verde e i batteri viola, contribuirono a questa prima diversità fototrofica.Una tappa evolutiva significativa fu lo sviluppo della fotosintesi ossigenica da parte dei cianobatteri. Questi microrganismi utilizzavano l'acqua come donatore di elettroni, produendo ossigeno molecolare come sottoprodotto. I cianobatteri colonizzavano ambienti marini poco profondi, formando estesi tappeti microbici. Col tempo, questi tappeti accumularono sedimenti e precipiti, fossilizzandosi in stromatoliti—alcune delle più antiche prove conosciute di vita. Con l'aumento locale dei livelli di ossigeno, reagiva con l'abbondante ferro disciolto nell'acqua di mare, precipitando sotto forma di ossidi di ferro. Questi ossidi si depositarono sul fondale marino, generando formazioni di ferro a bande (FIR), che fungono da principali indicatori geologici dei primi cambiamenti atmosferici.Una volta che la maggior parte del ferro oceanico fu ossidata, l'eccesso di ossigeno iniziò a diffondersi nell'atmosfera, scatenando il Grande Evento di Ossidazione (GOE) circa 2,4 miliardi di anni fa. Questa transizione alterò drasticamente la chimica e la biologia della Terra. L'aumento dell'ossigeno atmosferico ha permesso l'evoluzione della respirazione aerobica, che fornisce molta più energia rispetto al metabolismo anaerobico. Ha inoltre portato alla formazione dello strato di ozono stratosferico (O₃), che protegge il pianeta dalle dannose radiazioni ultraviolette e apre la strada all'espansione della vita sulla terraferma.Sebbene il GOE abbia promosso l'innovazione evolutiva, introdusse anche stress ossidativo e causò l'estinzione di molti organismi anaerobici. Tuttavia, l'avvento della fotosintesi ossigenoica rimane uno degli sviluppi evolutivi più significativi nella storia della Terra.

Origine della fotosintesi

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

Didattica

JoVE Core

Microbiology

Microbiologia

Unit

Unità

Microbial Evolution

Evoluzione microbica

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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.

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9-12.EVS.3.5

How Photosynthesis Changed Earth

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