by John Akers
“Can’t say I could tell them apart,” said Pax, while wondering why she was showing him these things.
“For a long time, neither could microbiologists,” said Alethia. “Neither of them has a cellular nucleus, and neither can form more than a single-celled organism. For a long time, it was thought bacteria were descended from archaea, but in the 1990s researchers discovered enough genetic and structural differences that it became clear they were separate life-forms.”
The pictures of the cells faded out and were replaced by the rocky surface of a seafloor all around them. Tall columns of bubbles rose rapidly out of many different places on the ground.
“Archaea got their start as extremophiles, living in environments such as these hydrothermal vents in the Pacific Ocean, where the temperatures can reach as high as 250 degrees Fahrenheit. Many now exist in much more mundane places, such as those in our intestinal tract that help with our digestive process. And while some bacteria are extremophiles as well, as a whole they are far more prevalent, existing in every habitat on Earth. Despite their tiny size, the biomass of bacteria exceeds that of all plant and animal life put together.”
The point of view shown on the walls began rising along with the bubbles from the hydrothermal vents. The darkness faded into an ever-lightening blue, and a few moments later, the viewpoint broke through the surface of the water. In front of them was a coastline, with what looked like hundreds of giant pancakes splattered across the shore.
“Stromatolites, 3.7 billion years ago, on what later became the western coast of Australia,” said Aleathia. “They were a type of sedimentary, rock-like formation inside which one type of bacteria evolved an early version of photosynthesis to produce the energy it needed to survive. As with plants today, the by-product of this process was oxygen. Initially, the oxygen was absorbed by iron and limestone in the Earth’s crust, but over hundreds of millions of years those became fully oxidized, and excess O2 began accumulating in the atmosphere. The ultraviolet radiation from the sun then transformed some of it into ozone, O3, which in turn led to the formation of the ozone layer in the stratosphere. As the ozone layer thickened, it reflected greater and greater amounts of the sun’s radiation, eventually blocking out all but one to two percent.
“Somewhat ironically, the high concentration of oxygen in the air was toxic to most of the life-forms at that time, and led to the first of several mass extinctions of life on Earth. However, the life forms that were able to adapt to the new atmosphere were no longer subject to the mutating effects of the sun’s radiation.”
“I see,” said Pax. “Just out of curiosity, why are you showing me all of this?”
“Because it provides important context for what’s to come.”
Pax looked at her skeptically. “All right, I guess.”
More versions of one-celled organisms appeared, some circular or ovoid in shape, while others were blobs with no particular shape at all. Many had no obvious means of movement, but a few had flagellate tails or tiny cilia covering it that rhythmically rippled to propel itself forward.
“Two and a half billion years ago,” Alethia continued, “the third form of life still in existence today, eukaryotes, appeared. Eukaryotes possessed a cellular nucleus, which acted as a central processing unit that eventually enabled them to form complex multicellular organisms. However, multicellular eukaryotes didn’t emerge for almost two billion years. Until then, eukaryotes remained unicellular, just like archaea and bacteria. Modern examples of single-celled eukaryotes include amoeba, paramecium, single-celled algae, and yeasts.”
The view suddenly plunged back down into the water. As darkness soon surrounded them again, something occurred to Pax.
“Hang on,” he said. “You said those are the only three forms of life. What about viruses?”
“Viruses aren’t considered life-forms, although it’s somewhat a matter of definition. Life is defined as an organism that is self-sufficient and self-replicating. Viruses have no cellular structure of their own and can only replicate inside the cells of other organisms so they aren’t considered living organisms in the same sense.”
As Pax considered this, a faint light appeared around them. Now he saw they were once again on the sea floor, only this time they were surrounded by primitive sea creatures. Jellyfish and sea worms drifted through the water, while starfish, sea cucumbers, and sea urchins all inched along on the sea floor. Nearby, some sea sponges and anemones appeared but remained stationary on nearby rock formations.
“Then, 600 million years ago, multicellular eukaryotes appeared. Sponges were the first, but the sea worm evolved the basic characteristics of most animals still living today: a mouth, an anus, an alimentary canal, bilateral symmetry, and a means of self-propulsion.”
The animals all suddenly disappeared and were replaced by ones that looked like enormous insects, some more than two feet long. One resembled a horseshoe crab with segmented casings and stubby, chitinous legs that churned rapidly. Another looked like a giant spiny slug, while another looked like a giant millipede with no legs, a long nose, and five eyes. It was followed by what looked like squid arms emanating from a long, conical shell.
“Feels like I’m in Mos Isley,” Pax joked. He glanced over and saw a smile flicker across Alethia’s face before she resumed talking.
“Starting 540 million years ago,” she said, “all the major animal phyla we know today, including mollusks, echinoderms, arthropods, and chordates, developed in only 30 million years. But despite the explosion in the number and variety of life-forms, the process by which the genetic information in DNA is transcripted from one generation to the next remained the same. As far as we can tell, it isn’t a very efficient process. In humans, less than five percent of the overall genetic sequence is used to encode the proteins that carry out all the cellular functions needed for us to survive.”
“Must’ve been designed by the government,” Pax joked. He looked back over the images of the early animals. “So they have no idea what the other 95 percent is for?”
“Some of it defines certain types of RNA. Other parts define chromosomal behaviors, such as centromeres, which is the point where chromosomes link to form an ‘X’ shape. Others define telomeres, which are where chromosomes terminate. But a great deal of the sequence remains a mystery.”
At the mention of telomeres, Pax involuntarily stiffened. He glanced over at Alethia to see if she’d noticed. To his dismay, he found she was looking right at him.
“Is something wrong, Mr. Pax?” asked Alethia. Her eyes were intense, probing.
“No, everything’s fine,” Pax said. Fortunately, Alethia didn’t press the matter and turned her attention back to the images in front of them.
Now, a bizarre-looking fish appeared. It had only a small, fixed opening for a mouth and a single dorsal fin that ran from its head all the way down and underneath its tail.
“The first fish,” said Alethia, “490 million years ago.” Soon after, another fish appeared, now with hinged jaws and a single pair of stubby fins. “It took another 70 million years before the evolution of the first lobe-finned fish, whose two fins were each connected to its body by a single bone. A branch of these, of course, evolved into modern ray-finned fish, whose fins consist of a web of skin held together by multiple spines. But the lobe-finned fish is also of particular importance to us, as it is the ancestor of all four-limbed land animals.”
The fish suddenly transformed into a weird-looking creature resembling a cross between a fish and a giant salamander. It swam toward them, then did a 180-degree turn and swam up and away from them. The point of view followed it, eventually breaking through the surface of the water again. Now Pax could see the salamander fish awkwardly waddling about on the land, its limbs splayed out perpendicularly to its body.
“400 million years ago, the first tetrapods, along with arachnids such as scorpions, began making the first forays onto land.” Pax noticed algae and rudimentary plants had already begun to develop on the land near the wa
terlines, as well as several types of seed-bearing plants and trees with fern-like leaves. Then an image of a large egg with mottled yellow and white colors appeared in the sand near the water.
“Then, 330 million years ago,” said Alethia, ”amniotic vertebrates began laying their eggs on land rather than in water. Relatively soon afterward they split into two main branches, one of which evolved into reptiles, dinosaurs, and birds, and the other into mammals and related animals. All other mammal-like creatures eventually became extinct, but so did most forms of life, thanks to three extinction events that occurred over a 200 million year period.
“The first occurred 250 million years ago, and was the most severe extinction event ever to happen on Earth. Ninety-five percent of all life was wiped out in less than 60,000 years. It was followed only 20 million years later by another that eliminated 50 percent of the species that had managed to recover from the previous one. Dinosaurs appeared shortly before the second event, but were small in size and managed to survive it. Afterward, they grew tremendously, and became the dominant form of animal life for the next 150 million years.
A number of smaller mammal-like creatures now appeared. Most resembled rodents or squirrels, while some were larger and looked more like badgers, or beavers with long flat tails.
“It was after the second event that the early mammalian ancestors appeared. Like dinosaurs before them, they started out small, getting by as nocturnal insect-eaters or attacking the nests of smaller dinosaurs. But early on they evolved a uniquely mammalian feature, the neocortex region of the brain, which eventually came to manage a number of higher-order functions such as cognition, sensory perception, and language.”
Their viewpoint rose rapidly into the air, until they were 50 or more miles above the surface. Suddenly, an asteroid came hurtling in from off to their right, moving so fast Pax barely caught a glimpse of it out of the corner of his eye. As it crashed into the ocean near a shoreline, an enormous, low rumbling filled the air. A gigantic cloud of dust flew up and slowly spread all over, eventually covering the land completely.
“The third extinction event was caused by an asteroid that collided with the Earth 66 million years ago on what is now the Gulf of Mexico,” said Alethia. “At least 6 miles in diameter, it struck with a force 2 million times greater than the largest nuclear weapon ever detonated, setting off volcanic eruptions all over the Earth. Massive amounts of sulfuric acid and other toxins spread throughout the stratosphere, blocking out the sun and dropping worldwide temperatures by as much as 50 degrees Fahrenheit. Seventy-five percent of all animals and plants species were killed off, including, most famously, all non-flying dinosaurs.”
“How do they know it was caused by an asteroid?” asked Pax.
“The fossil record shows a high level of iridium suddenly appeared all over the planet at this time,” said Alethia. “Iridium does not occur naturally on Earth, but is commonly found in asteroids.” Pax shrugged and nodded in acceptance.
The dust clouds cleared and their viewpoint moved back down to the surface. As they descended, Alethia said, “With dinosaurs out of the way, mammals grew quickly in size and variety. Around 90 million years ago—well before the extinction event you just saw—mammals had already diverged into primates and primate-like animals in one group, and all other mammals—dogs, cats, cows, horses, whales, moles, and so on—in the other. The primates then branched into a ‘wet-nosed’ group that includes our modern lemurs and lorises, and a ‘dry-nosed’ group consisting of monkeys and apes. Monkeys split off into their own line about 40 million years ago, then the lesser apes—gibbons—diverged from the great apes around 17 million years ago.
The viewpoint reached the surface again, and now they were facing a thick forest of trees.
“The great ape ancestors differed from all other animals in several significant ways,” Alethia continued. “For one, they sported considerably larger brains, proportionally speaking, than other animals. They also began evolving opposable thumbs, allowing them to grasp and manipulate external objects in ways no other animals could. And last but not least, they developed complex social structures that enabled them to operate collectively in ways other animals did not.”
A gray-haired animal that looked like a large monkey but with the broad face and flat cheeks of an orangutan appeared in the trees, swinging nimbly from branch to branch. Then it morphed into what looked much more like a modern orangutan. At the same time, there was a loud thud, as if an animal had suddenly dropped out of the trees to the ground.
“Fourteen million years ago,” said Alethia, “orangutans branched off on their own. The sound you just heard was the unknown ancestor of the remaining line, for whom there is essentially no fossil record, but we assume became more land-dwelling rather than arboreal, based on its descendants.”
Out of the trees came a gorilla, a large silverback, walking slowly forward on its knuckles. It stopped some twenty feet away from Pax and Alethia and regarded them, frowning. Suddenly it reared up and roared, beating its chest powerfully with its hands. It was so realistic Pax couldn’t stop his insides from clenching in fear and recoiling a couple of steps before catching himself.
To his relief, the gorilla suddenly disappeared and a chimpanzee emerged from the trees instead. It stopped at the same place the gorilla had, again eyeing Pax and Alethia suspiciously. Suddenly it too started shrieking and jumping up in anger. It grabbed a rock from the ground and hurled it just over their heads, then it grabbed a branch and started rushing toward them. Not five feet away, it too disappeared.
“Eight million years ago,” said Alethia, “gorillas split onto their own branch, followed by chimpanzees a million years after that. The remaining group was known as hominins.”
The tree line in front of them disappeared and was replaced by a flat desert plain that stretched out indefinitely, the bleak landscape only punctuated occasionally by a solitary tree or two. In front of them, an apelike animal with a shaggy coat of fur appeared. However, the fur was sparse enough in some places that Pax could see pink skin underneath. The face was decidedly ape-like, with wide cheekbones, a low forehead, and a jaw that jutted forward. Its neck was still hunched forward, however, as if it was still uncomfortable with its newfound vertical stature. But as it sidled past with an awkward, shuffling gait, Pax noticed the eyes were clear and bright. Overall, it looked roughly half ape and half human.
Alethia spoke again. “One of Hominins’ distinguishing characteristics was its ability to walk for prolonged periods on two feet instead of four. The other was its use of tools.”
A creature that was clearly more human than apelike appeared about 10 feet away, hunched over some large rocks on the ground holding a stone in its hand and forcefully striking it against another, larger stone on the ground. Much of the body and facial hair had disappeared, and the head and neck were now held fully upright.
“Two million years ago,” she said, “our ancestors Homo Erectus had evolved. Their brains had doubled in size relative to their hominin ancestors, and they possessed both the hand strength and precision grip needed to create a variety of simple stone tools. By chipping sharp edges in rocks, they could construct rudimentary tools such as hand axes. Perhaps most significantly, Homo Erectus learned to make fire and cook meat. The addition of cooked meat into their diets subsequently led to even more rapid cranial development.
“Evolutionary changes to vocal physiology enabled these early ancestors to use a guttural proto-language to communicate verbally. Their fully upright posture enabled them to see and walk farther than before, and they began hunting animals in coordinated packs over long distances. Over time they developed a hunter-gatherer division of labor.”
Next, an image of what looked like a small, male aboriginal with a frizzled mop of hair and a roughly shorn beard appeared. “Then, somewhere between 200,000 and 300,000 years ago, Homo Sapiens Sapiens evolved. Genetically speaking, this is us. Our brains had doubled in size again, and we had mastered the use of fire
and living in caves to protect ourselves from the elements. By 150,000 years ago, we had figured out how to skin other animals and treat the hides so they could be worn for warmth and protection. Our skeletons had become considerably lighter, reflecting our increasing reliance on technology, rather than biology, to cope with the demands of our environments.
“Fifty thousand years ago our tool use began to increase dramatically. We learned how to make more advanced stone tools, such as finely chipped scrapers and slicers, as well as tools for more specialized tasks, such as fish hooks made out of bone. As a result, we not only survived but thrived during a prolonged cold spell from 40,000 to 30,000 years ago. For unknown reasons, our close cousins the Neanderthals failed to adapt and became extinct.”
“We began to paint our bodies, wear jewelry, make cave art, and bury our dead. We developed more sophisticated means of hunting larger animals, like coordinating with each other to drive them over cliffs. We developed the first bow and arrow and the first ovens. We created fibers from flax and began weaving. We also began creating art, such as cave paintings and sculptures.”
Suddenly, the darkness that had surrounded the images immediately in front of them began to lighten. To his astonishment, Pax realized the large spherical room they had been in was gone. Now they were standing near the center of a huge circular room perhaps 100 feet in diameter and 50 feet high. The walls and floor were white, but the ceiling, strangely, was jet black.
In the center of the room there three white, circular disks. One was larger, about four feet wide and half a foot thick. It lay flat but somehow seemed to be hovering about three feet off the ground. The two smaller disks were positioned on opposite sides of the larger one, and were half its width and thickness. They were also suspended in the air, slightly below the larger disk.
Looking up again, Pax saw there didn’t seem to be a ceiling per se, just an eerie darkness. He felt like he was staring at a black hole.
Alethia walked over to the disks and Pax followed. Pax tried to see what was holding the disks up, but he couldn’t detect any wires above or supports underneath. On top of the larger disk, he saw there were two tall glasses containing a clear liquid. She picked them up and held one out to Pax. He took it but then hesitated, watching her. She took a long drink, then said, “Water, with some special additives for a pick-me-up.” Pax took a sip. It tasted like water. He drank some more.