If there was a time machine, where and on what date would they travel? We have all asked ourselves that at some point or it has been a topic of conversation between friends, family and/or acquaintances.
Whenever I am asked this question, I answer that I would love to travel to the four periods that seem to me to be the most surprising in the biological history of our planet, without first taking a 5-second tour of the origin of life, just 5 seconds to avoid dying of suffocation and heat.
We are 4.6 billion years ago, in the Hadean, when our planet Earth originated. Our planet was a red sphere, without an atmosphere and without oxygen, and with immense volcanic activity and solar radiation, huge explosions filled our planet and the heat was unbearable.
As the years passed, 3.7 billion years ago life originated in the Archaean; the first organisms were chemosynthetic and photosynthetic (bacteria and archaea) that lived on the surface and depths of the ocean. They are microscopic but extraordinary beings that generate their own food by absorbing bright sunlight and water, thus releasing oxygen.
The oldest fossil is a stromatolite, that is, a group of cyanobacteria from 3.5 billion years ago.
As time passed, in the Proterozoic, another type of unicellular organisms began to emerge, eukaryotic organisms. One of the most accepted theories (the endosymbiotic theory) explains that single-celled prokaryotic organisms (bacteria and archaea) began to live inside other prokaryotic organisms, taking on the function of a cellular organelle to convert food into energy, functioning as mitochondria or chloroplasts. These organisms began to evolve and generate specialized organelles to perform more complex functions, such as the nucleus (where DNA is packaged and protected), thus generating eukaryotic organisms.
These eukaryotic organisms began to generate colonies and live collectively to protect themselves and feed more efficiently. In order to transmit information from one to another and fulfill the tasks assigned to each one, they began to communicate through cellular connections, thus giving rise to multicellularity and generating new ecosystems in the ocean.
During this period, approximately 600 million years ago, the ocean was full of very curious, soft-bodied, soft and spongy organisms that looked like leaves and feathers; they fed on microorganisms, they were filter feeders. Their structure was very different from that of the animals we know today, which is why they have no current representatives; previously, it was believed that they were ancestors of sponges, jellyfish, annelids (such as worms) or echinoderms (starfish, sea cucumbers, etc.), however, they were organisms that lived only at that time, they became extinct and never existed again.
They were found in parts of North America, South America, Europe and parts of Asia, Africa and Australia. In Mexico there is evidence of these organisms in Sonora.
At the end of the Ediacaran period, oxygen began to increase, so immense and diverse organisms began to emerge in the ocean.
In the Cambrian (540 million years ago), an explosion of diversity of organisms emerged, unlike the Ediacara fauna, these are like those we know today, with shells and cephalization (head). These animals lived in shallow, shallow waters. They lived under or on the sediment (benthos), some swam in the water columns (nekton) and others floated wandering on the sea surface (plankton).
Those found in the sediment were excavators and moved inside the substrate, building secret tunnels, others moved on the sediment (walking), such as trilobites. They lived on the floors of the reefs, they were very diverse and abundant, they had sensory protuberances on their heads (antenna type) that they used to detect prey and thus capture them more easily.
And finally, on the surface of the water, there were small animals that lived in suspension and moved passively by ocean currents.
It was an amazing period, the one that impresses me the most, the forests in the Carboniferous were extraordinary, they were full of giant plants that measured up to 35 meters and a great diversity of plants such as ferns, sphenophytes, cordaites, and lycophytes.
The Carboniferous forests were very humid, swampy and full of giant insects, such as cockroaches that measured up to 9 cm in length and the Meganeura, an insect related to today's dragonflies that had a wingspan of up to 75 cm.
This period may be very familiar to you; during this time there were dinosaurs on planet Earth.
Do you know the name of any dinosaur? What is your favorite?
Some dinosaurs that lived in this period were the following:
- Sauropods, those giant herbivorous dinosaurs.
- The Ornithischians, they walked in a herd like the Iguanodon.
- The Triceratops, these fed on cycads and ferns.
- Tyrannosaurus rex were carnivorous and dominated the late Cretaceous in the North.
- The Spinosaurus were dinosaurs that were abundant in the south.
In addition, other creatures lived from these organisms, such as frogs, salamanders, turtles, crocodiles and snakes that lived on the coasts.
The Cretaceous ended when multiple meteorites collided with the earth and these animals became extinct.
Tell us in the comments section, what is your favorite period?
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Díaz-Sibaja, R. (2015). Ediacaran biota, the first eumetazoans in the fossil record. Nicolaite Science (66); 41-61.
Dieguez, C. (2003). Fauna and Vegetation during the Jurassic and Cretaceous. Monograph Garden Bot. Córdoba (11); 53-62.
Hornung-Leoni, C. T and Pulido-Silva, M. T. (2009). Traveling from the Carboniferous to the Jurassic: a story told through plants. Herreriana Magazine of Science Dissemination. Darwin Special Issue 2009.
Rangel-Galván, M. (2021). The Cambrian explosion: a unique phyla diversification event. Elements 121; 23-28.