The list is long – as long as life has been around on Earth – but it's still interesting.
Follow the journey back in time billions of years below, and stay informed about the journey of life on Earth, as reported by the British newspaper “Daily Mail”. NewScientist And what scientists already know about each step of its evolution.
3.8 billion years ago
This is science's current estimate of the beginning of life on Earth. During this period, something gave rise to two groups of organisms: bacteria and archaea.
Until now, scientists suspect that these life forms evolved from alkaline hydrothermal vents on the seafloor. Furthermore, researchers believe that these organisms contained genetic material based on RNA (not DNA).
However, there is little certainty about this period. Therefore, it is still necessary to know when, how and in what order bacteria are separated from archaea.
3.5 billion years ago
The oldest fossils of single-celled organisms date from this time, about 300 million years after the first sign of life. Even a little later, about 3.46 billion years ago, they began feeding on methane, according to the researchers.
Recently, scientists discovered that some rock formations in Western Australia are actually fossilized microbes dating back to 3.4 billion years ago, also around this period.
3 billion years ago
According to researchers, science knows that at this time of development Viruses already exist. However, they may have appeared at this time or even earlier, with the first signs of life.
2.4 billion years ago
The “Great Oxidation Event” is believed to have occurred during this period. It refers to the period when iron in the oceans oxidized, causing the metal to sink and create natural formations on the sea floor.
Some scientists believe this indicates the presence of photosynthetic cyanobacteria, meaning they produce oxygen. For them, production led to the element accumulating on Earth, so that it was stored in the atmosphere.
However, some researchers have recently refuted this idea. For them, cyanobacteria evolved later. Therefore, they believe that other bacteria oxidized iron during this period, even without the presence of oxygen.
2.3 billion years ago
Research indicates that the ground froze during this period. It is a possible first “ice world.” According to science, this could be a result of the lack of volcanic activity at that time.
Then, when the ice melted, it released more oxygen into the atmosphere.
2.15 billion years ago
The most reliable fossil evidence for the presence of cyanobacteria dates back to this period. Therefore, perhaps at this time oxygen began to accumulate in the Earth's atmosphere.
However, there are researchers who defend the hypothesis that O2 buildup is only due to the presence of another factor: a decline in methane-producing bacteria. This is because methane reacts with oxygen, removing it from the atmosphere.
2 billion years ago
At this moment of development, a simple cell fused into another, forming the first eukaryotic cells – those containing organelles. In the nucleus, DNA remained.
Meanwhile, other compact bacteria generated mitochondria, which provide energy. For example, cyanobacteria gave rise to chloroplasts, organelles that enable photosynthesis in plants.
1.5 billion years ago
About 500 million years after their appearance, eukaryotic organisms (which are still single-celled) are divided into three groups: plants, fungi, and animals. Thus, each strain develops separately. However, scientists still don't have answers about the order in which this happened.
900 million years ago
The first multicellular organisms were developed around this time. According to the researchers, this may have happened due to the formation of a colony of single-celled organisms, which ended up forming another colony, containing more than one cell.
800 million years ago
After unicellular organisms differentiate into the animal lineage and then become multicellular, they begin to divide into groups. The first are sponges, then placozoans.
In general, they are plate-shaped organisms with only three layers of cells, and are probably the last common ancestor of all animals.
770 million years ago
Once again, the planet freezes. About 40 million years later, jellyfish separated from other multicellular animals, as did cnidarians.
630 million years ago
Around this time some animals develop and begin to form upper and lower parts, front and back. This is called bilateral symmetry.
Perhaps the first animal to exhibit this characteristic was a type of worm Vernanimacula guizhouenawhose first fossil record dates back to about 600 million years ago.
590 million years ago
Another stage in the evolution of animals. After developing bilateral symmetry, they divide into protostomes and deuterostomes. This happened based on the way the embryos in each group developed.
Protostomes are those that generate the mouth through their first opening. They became arthropods (insects, spiders, crabs, shrimp, for example), in addition to microscopic worms.
Deuterostomes are those that generate the first anus. It gave rise to all vertebrate animals that exist today.
570 million years ago
At this point, there is another division: the echinoderms, which produced animals like sea stars, separated from the rest of the deuterostomes. They thus form a group known as Ambulacraria.
Only 5 million years later, some animals began to move on their own. At least, that's what fossil traces from that time indicate.
540 million years ago
Among the deuterostomes are the first chordates, animals with a backbone – or at least a primitive version of it.
About 5 million years later, the Cambrian explosion begins, a period in which many new body types appear.
530 million years ago
The first evidence of a vertebrate animal dates back to this period, which probably evolved from a fish without a jaw, but with a notochord, a rigid cartilaginous rod.
The first fossils of invertebrate animals (trilobites) also date from this time.
About 30 million years later, some animals began exploring the Earth, according to fossil evidence.
489 million years ago
At this moment, the so-called Great Ordovician Biodiversity Event begins. This occurs when there is a significant increase in the diversity of animals and plants.
After a few million years, plants began to colonize the land and fish split between the bony group and the cartilaginous group.
440 million years ago
Bony fish are divided into two main groups: lobe-finned fish, meaning those with bones in their fins, and ray-finned fish. The first gives rise to amphibians, reptiles, birds and mammals. The second group is the one that produced the majority of living fish species today.
After that, coelacanths and lungfishes separate from the lobe-finned fish group.
400 million years ago
The earliest evidence of insects dates back to this period. Also during this period, some plants develop and begin to have woody stems, like trunks. The first fossilized tree dates back to 15 million years ago.
397 million years ago
The first four-legged animals called tetrapods appeared. According to scientists, they likely evolved in shallow freshwater environments and then invaded land, giving rise to amphibians, reptiles, birds and mammals.
340 million years ago
The first major division occurs in tetrapods, with the amphibians separating from the others. After 30 million years, sauropsids and synapsids also separated.
Sauropsids include all modern reptiles, along with dinosaurs and birds. The first synapsids are also reptilian, but have different jaws, thus resembling and evolving from mammals.
320 to 250 million years ago
The first large group of webbed animals, called pelycosaurs, dominated the land. They're not dinosaurs yet.
275 to 100 million years ago
Therapsids, close relatives of pelycosaurs, evolved alongside them. They then began to replace their “cousins” in dominating the Earth, and continued until the beginning of the Cretaceous period, 100 million years ago.
During this period, a group of their teeth grow. These animals, called cynodonts, would evolve into the first mammals.
250 million years ago
At that moment, the largest mass extinction in Earth's history occurred, with many species exterminated. As the ecosystem recovers, the sauropsids now take over – it's now the world of dinosaurs.
Some ancestors of mammals lived as small nocturnal creatures. Meanwhile, marine animals that are cousins of octopuses are evolving in the oceans.
200 million years ago
As the Triassic period comes to a close, another mass extinction occurs, paving the way for dinosaurs to replace their sauropsid cousins.
Meanwhile, proto-mammals evolved the principle of homeothermy—the ability to maintain their internal temperature regardless of external conditions.
180 million years ago
At this moment the first division occurs between mammals: those that lay their eggs separately from others. A few monotremes are still alive today: they include the platypus and the echidnas.
Furthermore, evidence suggests that the first bird, called Archeopteryx, lived in Europe about 30 million years later.
140 million years ago
Around this time, placental mammals separate from marsupials. 10 million years later, the first flowering plants appeared.
105 and 85 million years ago
Once again, mammals are divided. Now, the placentas are divided into four main groups. Laurasians form a highly diverse community that includes hoofed mammals, whales, bats, and dogs.
Meanwhile, euarchontoglyrians are secreted by primates and rodents. Xenarthra includes anteaters and armadillos, and finally, Afrotheria gives rise to elephants.
100 and 93 million years ago
As Cretaceous dinosaurs reached their peak size, many marine invertebrates died out as the ocean ran out of oxygen. Scientists believe that this happened due to a huge underwater volcanic eruption.
75 million years ago
Rodents become a highly adapted and successful group. Therefore, they currently represent about 40% of modern mammalian species.
65 million years ago
Dinosaurs go extinct, paving the way for mammals to take over the planet. Two million years later, primates split into two groups: the haporrhinids, which have a dry nose, and the strepsirrhines, which have a wet nose. The second group develops in monkeys, apes and humans.
55 million years ago
According to scientists, the Paleocene/Eocene extinction occurs due to the rapid increase in the concentration of greenhouse gases. This leads to rising temperatures and the extermination of many species that live in the deep sea.
Only five million years later, artiodactyls began to evolve into whales.
40 million years ago
The New World monkeys become the first apes and separate from the rest of the group and colonize South America, after which the great apes begin to separate.
For 14 million years, orangutans spread throughout southern Asia, while their relatives remained in Africa. 7 million years ago, gorillas separated from other great apes.
6 million years ago
According to studies, during this period humans separated from their closest relatives, chimpanzees and bonobos. Soon after, human ancestors began walking on two legs.
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