Rising Complexity of Life

In the brief text titled “Rising Complexity of the Universe,” we explored the formation of stars, galaxies, the solar system, and Earth following the Big Bang. In this text titled “Rising Complexity of Life,” we will explain the formation of the Goldilocks conditions that permitted life’s emergence on Earth, the evolution from single-celled organisms to the emergence of mammals, and the perilous journey life has encountered, facing the threat of extinction, nevertheless, always finding a way to persist.

Stromatolites: the earliest evidence of life.

The Emergence of Life from the Cosmic Abyss

There are three main hypotheses regarding the origins of life. Firstly, Darwin proposed that life originated in small pools of warm water, which remains the predominant theory. The second hypothesis suggests that life emerged from organic chemicals near underwater hot volcanoes. Lastly, the panspermia theory proposes that life originated elsewhere in the universe and was transported to Earth via asteroids containing life.

The Evolution of Life

The evolutionary timeline unfolds with the emergence of life, beginning with single-celled prokaryotes inhabiting the ocean floor. As sunlight permeated the surface waters, these prokaryotes gradually migrated upwards, harnessing their warmth and energy for photosynthesis. This photosynthetic activity flooded the atmosphere with oxygen, precipitating the extinction of carbon dioxide-dependent organisms and paving the way for oxygen-respiring life forms.

Escalating Levels of Complexity

Subsequently, more intricate organisms, termed eukaryotes, arose, characterized by the presence of organelles within their cells.

As multicellular organisms evolved, specialized nerve cells emerged to facilitate complex functions, culminating in the development of consciousness.

Transitioning to land, plants and fungi enriched the soil, making it conducive for life. This transition attracted organisms to terrestrial habitats.

From Reptiles to Mammals

The first terrestrial inhabitants were fish-like creatures, succeeded by egg-laying reptiles. Over time, mammals evolved from reptilian ancestors, exhibiting warm-bloodedness and live birth, distinguishing them from their reptilian predecessors. Some mammals even displayed features like feathers, further diversifying life on land.

Five Eras and Extinction Events: Facing Calamities

While the odds of the Goldilocks conditions (optimal conditions) necessary for life to emerge are slim, they did materialize. Conversely, the likelihood of conditions capable of extinguishing life was considerably higher, and throughout Earth’s history, life faced the imminent threat of extinction on numerous occasions.

There have been five significant extinction events to date. Each event witnessed the extinction of various species, yet surviving species and their descendants persevered and thrived, perpetuating life’s resilience and adaptability, further complicating their existence.

Ordovician Era

This extinction event occurred during a time of abundant marine life, with sea levels significantly higher than today’s sea levels. The rapid cooling of the planet and the subsequent freezing of the oceans led to the demise of approximately 85% of marine species.

Devonian Era

This period saw the proliferation of fish species, with the emergence of lobe-finned fish, ancestors of four-limbed land vertebrates. Additionally, plant life on land evolved into towering trees, enhancing oxygen levels in the atmosphere. The cause of the significant extinction event during this period is attributed to rapid global climate fluctuations, resulting in the loss of around 70% of species.

Artist depiction of the “Great Dying.”

Permian Era

A time marked by drying forests and the rise of reptiles, including synapsids, the precursors to mammals. The Permian extinction, also known as the “Great Dying,” is the most extensive extinction event in Earth’s history. It resulted in the loss of 90% of marine species and 70% of land species. Volcanic eruptions in Siberia released gases that enveloped the atmosphere, leading to a dramatic cooling effect.

Triassic Era

Characterized by arid and hot conditions favourable for reptiles, this period witnessed the emergence and diversification of reptilian species. The cause of the extinction event during this era is theorized to be either an asteroid impact or volcanic activity. While most reptilian species perished, dinosaurs endured, marking the onset of the age of dinosaurs.

“The Crater of Doom” in Mexico, was formed by the impact of the meteorite thought to have caused the extinction of the dinosaurs.

Cretaceous Era

The era dominated by dinosaurs came to an abrupt end with the impact of a massive asteroid on Earth. This cataclysmic event led to the extinction of dinosaurs, creating ecological niches for the evolution of new mammalian species.

Conclusion

In this brief text, we explored the initial emergence of life and the perils of extinction it encountered. We’ve observed a progressive rise in complexity with each successive event. Following the texts “Rising Complexity of the Universe” and “Rising Complexity of Life,” the forthcoming text will explain the evolutionary journey of humans and their civilization establishment, titled “Rising Complexity of Humanity.”

References

• American Museum of Natural History. (n.d.) Mass Extinction Events. https://www.amnh.org/exhibitions/dinosaurs-ancient-fossils/extinction/mass-extinction
• BBC Ideas. (2022, December 29). Are we thinking about alien life all wrong? [Video]. YouTube. https://www.youtube.com/watch?v=KbRObyIqv1U&t=8
• Begum, T. (2023, February 21). What is mass extinction and are we facing a sixth one? Natural History Museum. https://www.nhm.ac.uk/discover/what-is-mass-extinction-and-are-we-facing-a-sixth-one.html
• Christian, D., et al. Big History. [MOOC]. Big history project. https://bhp-public.oerproject.com/
• Lotzof, K. (n.d.) Charles Darwin: History’s most famous biologist. Natural History Museum. https://www.nhm.ac.uk/discover/charles-darwin-most-famous-biologist.html
• National Geographic. (n.d.) Devonian era. https://www.nationalgeographic.com/science/article/devonian
• National Geographic. (n.d.). Ordovician era. https://www.nationalgeographic.com/science/article/ordovician
• National Geographic. (n.d.) Permian era. https://www.nationalgeographic.com/science/article/permian

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