This timeline was created for general audiences. Created by: Chrissy Christian, Daniel Dodinval, and Matt von Konrat, Field Museum of Natural History
Today's plants emerged from the broad group of chlorophyll-containing organisms called green algae. Many green algae live in fresh water and some even live on land. Recently, scientists discovered the oldest green algae fossils ever found - green seaweed fossils from about a billion years ago - suggesting that green algae probably dominated the seas for a long time before plants emerged and took over the land. Only one phyla of green algae are actually considered to be plants.
While monocots have just one seed leaf, eudicots have two. Formerly known as dicots, these plants are characterized by their branched leaf veins, thick taproots, and flowers with petals in multiples of four or five.
Monocots, flowering plants that sprout only one leaf from their seeds, are now seen in the fossil record. You can identify monocots today by their stringy roots, the parallel veins in their leaves, and their flowers, whose petals comin in multiples of three.
Red and brown algae first appear in the fossil record. These small photosynthesizers, like kelp and other types of seaweed, are their own group of organisms - they're no longer classified as bacteria, but they aren't considered plants, either.
The first plants with flowers and fruits, known as angiosperms, are now seen in the landscape. These species rely heavily on pollinators for fertilization and reproduction. Insects evolved significantly around this time, and it is believed that this impacted the evolution of these flowering plants.
The boundary between the Triassic and Jurassic periods is marked by Earth's fourth mass extinction event, which saw the end of up to 76% of all species due to volcanic activity, global warming, and generally changing climates. Most species of dinosaurs managed to survive the extinction, and with so much of their competition cleared out, this event cleared the way for them to dominate the planet.
It's hard to imagine 96% of all species on Earth dying at once, but that's exactly what happened at the end of the Permian period. In less than 100,000 years, 96% of all marine species and 70% of all land species were wiped out by rapid global warming, possibly caused by heavy volcanic activity filling the atmosphere with greenhouse gases and ash. There's a reason this event is sometimes referred to as the "Great Dying".
Cyanobacteria, the first organisms to produce oxygen, first appeared around this time. These water-dwelling bacteria have specialized parts called chloroplasts that photosynthesize sunlight into oxygen. The chloroplasts turn them a bluish color, which is why these organisms were previously known as "blue-green algae" - but we know now that they aren't algae, nor are they plants.
Gymnosperms were the first plants that produced seeds and didn't need water to reproduce. The word gymnosperm means "naked seed", referring to the cones they use to reproduce. Evergreen trees like pines and other conifers are gymnosperms.
The first living things to turn sunlight into energy, through a process called photosynthesis, weren't actually plants at all - they were tiny, single-celled bacteria. Unlike plants, they convert light to energy without the use of chlorophyll, the thing that gives plants their green color.
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Ferns were some of the first large plants on Earth. Many have large fronds that elegantly unfurl when they grow. Ferns reproduce by releasing spores into the air, rather than using flowers like many other plants.
Earth's second mass extinction event occurred late in the Devonian Period. Scientists have a hard time determining what exactly caused the extinction, but we do know that at least 75% of all species did not survive. The rise of land plants we're documenting here may actually be partially responsible, and it's because of how plants get their energy - photosynthesis. As plants began to spread across the planet, levels of oxygen in the atmosphere rose and levels of carbon dioxide sharply fell. Only species who could adapt to these changing conditions were able to survive.
The typical plants that you think of are finally here! Around this time, plants began to grow with stems, trunks and roots (known as the plant's vascular system), allowing them to grow taller and capture more light in a growing world. The first land plants laid the beds of carbon that are coal deposits today.
At the end of the Ordovician Period, life on Earth experienced the planet's first mass extinction, where 86% of all species were lost in the span of only about a million years. Scientists historically believed this occurred because of a global ice age that began and cooled the planet, followed by a period of global warming. However, recent studies suggest that it may instead have been the result of heavy volcanic activity.
The first plants to grow on land were small, lacking features like stems and roots that are required to grow big. They also reproduce without flowers. Many of these first land plants were bryophytes, a group of microscopic plants including mosses, hornworts, and liverworts.
The first humans evolved from our early hominoid ancestors.
The changes in climate and creation of tree canopies on land caused a boom of new epiphytic fern species (ferns that do not need to grow in soil). The mas
The age of the dinosaurs came to an end with Earth's fifth mass extinction event. At the end of the Cretaceous period, the planet was struck by a massive asteroid, causing widespread wildfires and producing a dust cloud that surrounded the planet and blocking out sunlight. This cooled the planet drastically and prevented plants and plankton from photosynthesizing. 76% of all species were lost in the aftermath. However, just like the fourth mass extinction cleared the way for dinosaurs to dominate, this extinction cleared the path for mammals to take over the Earth - including, eventually, humans.
Plants react to their environment, and when something changes in an ecosystem, other species have to evolve, too. Predatory insects, other herbivores, and a rapidly changing climate put stress on land plants around this time, causing massive in both land plants and animals.
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