First Plants on Earth
When the first plants appear. About 4,000 million years ago the first forms of life in the oceans appeared.
Thus, the first plant cells thickened its membrane and allowed the accumulation of food reserves.
Thanks to this process the emergence of the first microalgae could occur in the oceans, which later would generate descendants who were the ancestors of all terrestrial plants.
A little history
About 3,500 million years ago, moss, together with conifers and flowering plants, were the first plant population to abandon the marine environment to conquer the land.
The plant fossil of the primitive Vascular plant Cooksonia, constitutes the first evidence that locates the time in which the terrestrial plants appeared at the end of the Ordovician period and beginning of Silurico, of the Paleozoic era, about 450 to 470 million years ago; But the colonization of the earth by plants probably happened millions of years before its appearance.
The origin of the terrestrial plants coincides with a period of glaciation and mass extinction. It is possible that at that time atmospheric carbon levels were higher than those of today, and that oxygen and ozone levels were almost equivalent to the current concentration.
Half a million years ago certain forms of green algae made a permanent transition from the ocean to dry land, giving rise to terrestrial vegetation and aquatic upper plants (descendants of terrestrial ancestors).
The ferns are also living fossils preserved to this day and tell us how vegetation will have been in the early days.
The first plants with seeds were Conifers that appeared in the Second Age hundreds of thousands of centuries later initiating a new great vegetal civilization.
The first plants with seeds that are known the date from the Upper Devonian (about 370 million years ago).
Elkinsia polymorpha is the oldest fossil known in this group and consists of a few twigs with seeds. The fragment is small but very well preserved, which has allowed knowing numerous details of its anatomy.
It is proposed that moss emerged from an algae-like Coleochaete, but the Pteridophytes (ferns and other seedless vascular plants) originated from a branched green alga, which spatially separated the production of gametes and spores; Based on these evidences, a phylogenetic tree was constructed showing the relationship between green algae and the ancestor of modern terrestrial plants.
Plants with Leaves
The first plants with leaves were the mosses to which the fossil evidence assigns a very old origin. The mosses did not evolve, they did not adapt to the aerial life and although they possess lignin (the essential component of the wood to which it provides its rigidity), they did not know how to use it. Mosses, along with conifers and flowering plants, are the first plant civilization to leave the marine environment to conquer the land.
The first plants that ‘learned’ to take advantage of the wood were the ferns, which constituted thus the first great vegetal civilization adapted to the terrestrial life.
Four hundred million years ago, after a terrible drought that devastated the earth, the first erect plants appeared like the Rhinia.
Another later fossil is Archaeosperma arnoldii, in which four ovules are surrounded by elongated appendages that constituted a species of the dome.
These predecessors presented the seeds directly on the branches and did not have specialized structures around them. On the contrary, the present plants present the seeds grouped in cones or flowers.
From this time are the first modern forests, with large trees, with secondary growth in thickness.
One of the most well-known fossils, which must have been very abundant, is Archaeopteris, as it has been found in many localities with Detaitic rocks and very different latitudes.
In the Carboniferous, the plants with seeds were very abundant and already had diversified in numerous evolutionary lines of which remain numerous fossil remains.
From the Permian to the Upper Jurassic many of these lines were extinguished, and only five groups have reached the present time: cicadas, ginkgos, conifers, gneisses and angiosperms.
First Plant Lines
The origin of the first three lines goes back to the Paleozoic, the gnetales and modern conifers appeared between the Triassic and the Jurassic, and the angiosperms, later, in the Mesozoic.
During the Cretaceous and Jurassic all current lines decreased in number, except the angiosperms that experienced a great radiation.
As a result, the current lines vary markedly in diversity (number of species) and degree of divergence. Plants with current seeds are grouped into five divisions.
- Cycadophyta, 10-11 genera, 100-160 species (eg Cycas, Encephalarthos).
- Gynkgophya, 1 genus, 1 species (Ginkgo biloba)
- Pinophyta (= Coniferophyta), 65-70 genera, 600 species (eg Pinus, Larix, Abies, Cedrus, Juniperus, Taxus)
- Gnetophyta, 3 genera, 70 species (Gnetum, Ephedra, Welwitschia)
- Magnoliophyta, approx. 12,000 genera ,. 260,000 species. So let’s take care of planet earth.
A short video explaining a few key facts and concepts on land plant evolution from a phylogenetic perspective.
A great book I recommend is this.
- Linda Lowery
- Publisher: Lerner Publishing Group
- Edition no. 0 (08/01/2003)
- Encuadernación para biblioteca: 45 pages
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