Question 1

The main stages of the evolution of terrestrial plants

Accepted Answer

The Devonian (416 - 359 million years  BP) is the gilded age of vegetal innovation as roots, organisation into main and lateral stems, simple leaves emerged at that time in addition to two major revolutions : seeds, which allow for reproduction not being too reliant on water, and wood-forming tissue cambium, which makes height growth possible. The first forests take shape : forests mean photosynthesis, which, in turn entails a decrease in levels of atmospheric CO₂, a large scale process that was to pave the way for a global climate cooling. The Carboniferous (359 - 299 million years BP) sees plants expansding into wetlands. Lycophytes, giant horsetails and tree ferns constitute dense forests that will provide the raw material for present day coal deposits.The Permian (299 - 251 million years BP) . the lush forests are now gone. Enter  two groups better equipped to cope with droughts : the needle-leaved conifers and   the Ginkoales, an order consisting of only one species: the Ginkgo biloba or ginkgo tree.During the Triassic and Jurassic  (251 - 145 million years BP), ferns and horsetails are in decline whereas the conifers prevail in landscapes. In the  Cretaceous (145 - 66 million years BP), flowering plants (angiosperms) emerge and diversify. Around 90 million years BP,  the first grasses grow in the shades of tropical forests  (some remains were found between the teeth of herbivore dinosaurs  dating  90 million years BP).During the Cenozoic (66 million years BP - present),  angiosperms dominate. But in the Quaternary, ecosystems are turned on their heads by a force that needs to be reckoned with : human activity. As to what future holds in store is till unclear…

Question 2

What about us in the greater picture of things ?

Accepted Answer

Life is everywhere: it grows, it swarms, it dies, it burgeons. But at the end of the day, what is the breakdown ? Here are a few figures to put things in perspective.Terrestrial biomass  (the total mass of living organisms) :Plants : 82.5 %Bacteria : 12.8 % Animals* : 0.4 %Humans : 0.01 % * Animal biomass (the total mass of animals) :Arthropods : 41.9 %Molluscs : 8.4 %Cattle : 4.2 %Humans : 2.5 %We only account for just a tiny fraction of the terrestrial biomass, and a minute portion of  the animal biomass, outnumbered not only by the arthropods, but also by the cattle we raise.

Question 3

Funfact | Convergent evolution

Accepted Answer

Despite evolving separately,  species have to cope with the same environmental constraints  and therefore develop similar structures or functions. For example, bats  (mammals) and birds' (saurians) wings have evolved independently to enable flight.

A vessel to conquer dry land

The history of plants - much as that of life - began in the water. By acquiring sap-conducting vessels, plants could venture on further from wet environments . This innovation proved a transformative change in our planet's destiny .

Did you know ?

These prehistorical plants are still in existence:

Informations complémentaires

The main stages of the evolution of terrestrial plants

What about us in the greater picture of things ?

Funfact | Convergent evolution

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Cooksonia, dating back 425 million years, are the oldest vessel plants known to date. They were a few centimeters tall and had neither leaves nor flowers.