33.7
Colonização da Terra
Over three and a half billion years ago, lifeforms could survive only in aquatic environments. Later, some prokaryotes, such as cyanobacteria, began fixing carbon dioxide to produce sugars through photosynthesis.
These photosynthetic organisms released oxygen, and it accumulated in the atmosphere.
Evidence suggests that single-celled photosynthetic microbes colonized moist terrestrial surfaces more than two billion years ago.
While land environments provided abundant sunlight and carbon dioxide, two crucial components for photosynthesis, they also presented challenges such as desiccation, UV exposure, and lack of structural support.
Multicellular plants and fungi gradually evolved the ability to live on land around 470 million years ago.
This transition required several adaptations. Some cells formed shoots that capture light, while others formed root-like structures that anchor the plant and absorb water and nutrients.
Other structural changes also helped plants survive on land. For example, a waxy cuticle limited evaporation.
Cell walls provided structural support, while vascular tissue helped move water through larger plants.
Around 450 million years ago, arthropods were the first animals to evolve the ability to live on land.
These organisms had external skeletons and belonged to the group that includes modern insects, arachnids, and crustaceans.
Early tetrapods evolved around 380 million years ago. Their lobe-finned fish ancestors had features like lungs and stronger limb bones that helped them move from water onto land. They later diversified into amphibians, reptiles, birds, and mammals.
Plants that had already colonized land formed the base of early terrestrial food webs, supporting both arthropods and tetrapods. Through this gradual process, plants, fungi, and animals colonized Earth’s landmasses and eventually evolved into the diverse species that exist today.
Mudanças no ambiente da Terra primitiva impulsionaram a evolução dos organismos. À medida que organismos procarióticos nos oceanos começaram a realizar fotossíntese, eles produziram oxigénio. Eventualmente, o oxigénio saturava os oceanos e entrava no ar, resultando em um aumento na concentração atmosférica de oxigénio, conhecida como a revolução do oxigénio há aproximadamente 2,3 mil milhões de anos. Portanto, organismos que poderiam usar oxigénio para respiração celular tinham uma vantagem. Há mais de 1,5 mil milhões de anos, células eucarióticas e organismos multicelulares também começaram a aparecer. Inicialmente, todas essas espécies estavam restritas aos oceanos da Terra.
Os primeiros organismos a viverem em terra foram procariotas fotossintéticos que habitavam ambientes húmidos perto das margens do oceano. Apesar da falta de água, ambientes terrestres ofereciam uma abundância de luz solar e dióxido de carbono para a fotossíntese. Há cerca de 500 milhões de anos, os ancestrais das plantas atuais foram capazes de colonizar ambientes mais secos, mas exigiram adaptações para evitar a desidratação. Elas desenvolveram métodos de reprodução que não dependiam da água e protegiam os seus embriões de secarem. Essas plantas primitivas desenvolveram, além disso, um sistema vascular que incluía raízes para adquirir água e nutrientes e um caule para obter luz solar e dióxido de carbono.
Plantas e fungos parecem ter colonizado a terra ao mesmo tempo. A sua coevolução em terra é o resultado da relação mutualmente benéfica entre muitas plantas e fungos, vista tanto em organismos atuais como em alguns dos primeiros fósseis vegetais; Os fungos auxiliam na absorção de nutrientes e água, beneficiando-se dos nutrientes fornecidos pela planta.
Os artrópodes foram a primeira espécie animal a colonizar a terra, há cerca de 450 milhões de anos. Os primeiros tetrápodes evoluíram mais tarde para viverem também em terra, encontrando uma abundância de alimentos nas espécies vegetais que colonizaram a terra. Os anfíbios dominaram a vida animal terrestre por 100 milhões de anos. Mais tarde, dinossauros e mamíferos se tornariam os animais terrestres mais abundantes.
Over three and a half billion years ago, lifeforms could survive only in aquatic environments. Later, some prokaryotes, such as cyanobacteria, began fixing carbon dioxide to produce sugars through photosynthesis.
These photosynthetic organisms released oxygen, and it accumulated in the atmosphere.
Evidence suggests that single-celled photosynthetic microbes colonized moist terrestrial surfaces more than two billion years ago.
While land environments provided abundant sunlight and carbon dioxide, two crucial components for photosynthesis, they also presented challenges such as desiccation, UV exposure, and lack of structural support.
Multicellular plants and fungi gradually evolved the ability to live on land around 470 million years ago.
This transition required several adaptations. Some cells formed shoots that capture light, while others formed root-like structures that anchor the plant and absorb water and nutrients.
Other structural changes also helped plants survive on land. For example, a waxy cuticle limited evaporation.
Cell walls provided structural support, while vascular tissue helped move water through larger plants.
Around 450 million years ago, arthropods were the first animals to evolve the ability to live on land.
These organisms had external skeletons and belonged to the group that includes modern insects, arachnids, and crustaceans.
Early tetrapods evolved around 380 million years ago. Their lobe-finned fish ancestors had features like lungs and stronger limb bones that helped them move from water onto land. They later diversified into amphibians, reptiles, birds, and mammals.
Plants that had already colonized land formed the base of early terrestrial food webs, supporting both arthropods and tetrapods. Through this gradual process, plants, fungi, and animals colonized Earth’s landmasses and eventually evolved into the diverse species that exist today.
From Chapter 33:
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33.7 : Colonização da Terra
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33.1 : Condições na Terra Primitiva
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33.2 : O que é a História Evolutiva?
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33.3 : O Registo Fóssil
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33.4 : A Evidência da Evolução
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33.5 : Árvores Filogenéticas
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33.6 : Evolução Convergente
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