Forged in fire: Earth's past and future explored in 'Cosmos: Possible Worlds'

A young Neanderthal girl kneels at the water's edge as host Neil deGrasse Tyson looks on. Until about 40,000 years ago, our Neanderthal relatives lived very much as we did.
A young Neanderthal girl kneels at the water's edge as host Neil deGrasse Tyson looks on. Until about 40,000 years ago, our Neanderthal relatives lived very much as we did. (Image credit: Cosmos Studios)

Religion and worship are intrinsically tied with our history as a species, as is fire, and both are recurring motifs in this week's episodes of "Cosmos: Possible Worlds." 

At the beginning of episode 11, called "Shadows of Forgotten Ancestors," host Neil deGrasse Tyson reminds us that when Homo sapiens, which means  "wise ones," discovered and controlled fire hundreds of thousands of years ago, everything changed. Fire allowed us to cook food and heat dwellings, and it served as a focal point for storytelling and sharing cultural identity among community members. 

Persepolis, a complex built by emperors around 600 BCE when Persia was the only superpower on Earth, illustrates the central focus fire had in ancient civilization. The domestication of fire played a crucial role in the worship of the Zoroastrian god, Ahura Mazda, and symbolized the god's purity and the "light of the illuminated mind." 

Related: 'Cosmos: Possible Worlds' brings the search for E.T. down to Earth

Evil, catastrophe and disease, on the other hand, were caused by Angra Mainyu, the Zoroastrian representation of what modern Christian societies would call the devil. Why people thought of these maladies as being the creation of an evil being becomes more obvious as Tyson walks us through how a rabies virus invades a dog's body after the pup has been infected by a rabid bat. 

Disease microbes not only attack and kill cells, Tyson explains, but also change their hosts' behavior to facilitate the virus' spread to other hosts. The rabies virus, for example, turns its host into a fearless, crazed animal by attacking the limbic system, which deals with emotions and memory. Once the limbic system is compromised, the virus turns its attention to the mechanisms in the animals' throat that produce saliva, causing infected animals to foam at the mouth. The virus also inhibits the swallowing mechanism, maximizing the chances infected saliva will spread to another host. 

How does the virus "know" to do this? "Evolution by natural selection," says Tyson, explaining that "given enough time, a random mutation will take hold if it enhances the virus' chance of survival." Ironically, it's the victims that keep a virus' "wicked flame" alive as it leaps from host to host, bending them to its will as if it were a sentient being. "We are at the mercy of unseen forces; viruses, microbes, hormones, our very own DNA. Where does the programming end and free will begin, if it ever does at all?" 

Elaborating on these points, Tyson turns to insects and animals. Simple behavioral programs are abundant in the animal kingdom; for example, upon their death, bees secrete oleic acid (a "death pheromone") to tell their fellow hive members to remove their corpses from the hive, and geese will instinctively retrieve any egg-like objects that may have rolled away from their nests. While we may detect evidence of spontaneous decision-making in animals, Tyson says, can we identify a source of executive authority in them, or a "soul"? What about human beings? 

We don't yet have established parameters for what it means to be "distinctly human," Tyson notes. Plato was one of the first philosophers to put forth a definition: "Man is a featherless biped." Aristotle, a student of Plato's, would later proclaim that man is a social and political animal. Neither of these definitions hold much weight; after all, ants, bees, and termites are also social animals. Underscoring this point, Tyson gives us several examples of animal species that engage in trade and art, use technology and tools, parent their young through adolescence into adulthood, and who enslave and exploit other animals and keep them in captivity. Other animals even show each other affection and tenderness. 

Related: Creative creatures: 10 animals that use tools

On the Monterey Cliffs, "Cosmos: Possible Worlds" host Neil deGrasse Tyson gently rocks a newborn baby.

On the Monterey Cliffs, "Cosmos: Possible Worlds" host Neil deGrasse Tyson gently rocks a newborn baby.  (Image credit: Cosmos Studios)

It would seem the only thing that separates us from other animals, Tyson ponders, is our "neurotic need to feel 'special.'" Against the backdrop of the Halls of Extinction, featured prominently in previous episodes, Tyson insists that there must be a clear distinction between ourselves and animals that justifies our eating them, wearing them and even bringing an end to their species.

"Is DNA destiny, and if it is, does it have the power to write epic tales of heroism and saintliness?" There's heroism in the way a gazelle will put herself in harm's way to protect her offspring and herd from a cheetah, but there's also heroism in stories from our ancient past, as Tyson illustrates with the story of Ashoka. Five seconds ago on the "cosmic calendar" — approximately 2,200 Earth years ago — the emperor Ashoka's reign of terror over the Indian subcontinent began, marked by his proclivity for torture and extreme violence. 

After an exchange with an unnamed Buddhist monk, Ashoka underwent a profound change; having realized the true scope of his power, social welfare became Ashoka's top priority as his idea of "kinship" expanded to include everyone, even animals. He banned the ritual sacrifice of animals and established veterinary hospitals. Ashoka further dug wells, planted trees, built shelters, signed peace treaties with neighboring countries he once warred with, built schools, hospitals and hospices, introduced the education of women and free healthcare for all, and much more. 

"Ashoka's dream," Tyson says, referring to his philanthropic pursuits, "grows louder with time." We cut to a scene of a mother with her crying child, who had been born just moments before. We see the child again in the twelfth and penultimate episode of the series, "Coming of Age in the Anthropocene." The opening scene finds us on a placid seashore where Tyson describes life on Earth to the newborn. "We're all very young here," he coos, "new, like you, to the mysteries of the universe." Science, Tyson states, is our birthright and is how we piece together our history. 

Setting the stage for this new episode, Tyson recalls our own planet's fiery beginnings when it was hammered by a celestial body the size of Mars, which blasted into space material that became Earth's moon. Earth gradually cooled, forming a crust on its surface that allowed oceans to form. In our planet's infancy, days were much shorter; only about six hours long, notes Tyson. The environment was also toxic and hostile: "Scientists reason that the thick, hazy atmosphere trapped the heat of the Earth and made it scorching hot," Tyson explains.  

Related: How the moon formed: 5 wild lunar theories

Amazingly, there were organisms that survived this seemingly uninhabitable environment; these were cyanobacteria that lived deep in the oceans, and "remade" the planet by consuming carbon dioxide and producing oxygen, which in turn consumed the thick methane that enveloped our planet, causing temperatures to drop. Atoms of oxygen then gathered in the sky above our planet and formed ozone molecules. Life on land became possible, and the young Earth's landscape changed drastically as this life began to adapt to its new conditions. 

At 11 o'clock on New Year's Eve of the cosmic year, Homo erectus stood up for the first time, freeing its hands and earning the species its name. "They began to move around, to explore, daring to risk everything to get to unknown places. They were brave, and their blood runs in your veins," says Tyson of our ancient ancestors. Some explored Africa and others went on to Europe, and evidence supports the theory the European pioneers would later evolve into Neanderthals. Other H. erectus individuals would go on to Asia and evolve into our hominid cousins, the Denisovans.

Our Neanderthal relatives lived much as we did and did many of the things we consider to be "human," says Tyson. To this day, a few of us even carry some Neanderthal genes; however, some unknown force wiped out the Neanderthals and Denisovans many years ago. Scientists postulate it may have been their complacency that doomed them, as we have evidence showing they never ventured beyond ocean coastlines. 

More restless than their cousins the Neanderthals and Denisovans, our Homo sapiens ancestors crossed seas and unforgiving landscapes, changing the land, ocean and atmosphere, leading to mass extinction. The scientific community gave our age a new name, "Anthropocene," from the Greek words for "human" and "recent." Just as the Neanderthals and Denisovans may have doomed themselves, however, early Homo sapiens may have doomed their descendants: us. 

Altering our world comes at a great price; a "darkness," Tyson says, has been looming over us as our technology advances and population increases. The invention of agriculture allowed humans to settle on farms and later in cities. The carbon dioxide and methane released from various farming and agricultural techniques increased exponentially as our need for them increased, to sustain ever-growing numbers. In China we began burning coal, which became fuel for foundries, forges and homes. 

As harmful to the environment as these were, nothing compared to the damage done by chlorofluorocarbons, or CFCs. Before refrigerators, we kept food items cool and stored them in ice boxes. Later, the ice box was replaced by a gas-powered refrigerator that used ammonia sulfur dioxide as a coolant. However, these chemicals were poisonous and the mechanism would often leak, making them dangerous. The invention of CFCs, a molecule that hadn't existed in nature previously, was so successful it was used in almost everything. 

The catastrophic effect CFCs had on ozone was not discovered until the early 1970s, when chemists Mario Molina and Sherwood Rolland, studying the effects rocket fuel had on the atmosphere, found CFCs not only accumulated in the atmosphere, but had already thinned the ozone layer. When UV light hits a CFC molecule, it strips away the chlorine atoms, which then eat away at ozone, the very insulation that makes it possible to live on Earth. Thankfully, the scientists worked tirelessly to warn the world, and global governments heeded their warning; manufacturers stopped producing CFCs, and the ozone has been getting thicker ever since. Our children may even see the damage completely healed.

Related: The effects of global warming

The episode ends on a harrowing note, another scientists' warning we have yet to heed. Syukuro Manabe was born in rural Japan and took an intense interest in Earth's average global temperature. During the course of his career, he would assemble the evidence he needed to write "Thermal Equilibrium of the Atmosphere with a Given Distribution of Relative Humidity," a paper that predicted the increase of Earth's temperature due to greenhouse gases until it becomes an uninhabitable and toxic environment again, leading to our extinction. 

Many still believe the "science is unsettled," however, despite Manabe's correctly predicting the rise in temperature and its effects on our planet. "The scientists warned us," says a remorseful Tyson as we look into our future at life on Earth: lethal outdoor temperatures, global water shortages, wildfires. These ruminations culminate in the striking visual of battered baby bottles littering a dry and barren field, implying the worst for mankind. Tyson ends on a hopeful note, which will carry us into the final episode of the series. 

"This doesn't have to be," says Tyson. "it's not too late. There's another hallway, another future we can still have. I promise to get you there; we'll find a way."

"Cosmos" airs on the National Geographic channel on Mondays at 8 p.m. ET/9 p.m. CT and will be reprised on the Fox television network this summer.

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