Humans in the Universe
13 Billion - 200,000 Years ago
The Creation of Adam
A Pictorial Archive from Nineteenth-Century Sources. Mineola, NY: Dover Publications, Inc.
This Big Era and the Three Essential Questions
Humans are part of a universe that is older and larger than we can begin to
imagine. How was this universe created? How was the earth created? How and
when were our ancestors created? What is our place in the universe? Are we important, or
are we insignificant?
This Big Era sets the stage for human history. It is about the creation of our
environment, of the world we live in, its landscapes, its plants and animals. It is also
about the evolutionary steps that led to the creation of our species,
Homosapiens.
Understanding this era is vital if we are to grasp how human history fits into the larger
history of our earth and the universe as a whole. This is because our ideas about the
universe, the earth, and our own existence as a species affect how we think about
ourselves and our history. They help us understand our place in the larger universe of
which we are a part. So "creation myths," stories that help us understand how everything
around us came to be, seem to exist in all human societies.
Humans and the Environment
In the story of creation in the Bible’s Book of Genesis, God
made human beings. But he did so only after he had created
everything else that was to be part of his universe. The
creation took seven days. This is how it began in the
biblical account: "And God said, Let there be light:
and there was light. And God saw
the light, that it was good: and God
divided the light from the darkness.
And God called the light Day, and the
darkness he called Night."1 After making
day and night, God created the seas, dry land, grass,
fruit trees, the sun, the moon, fish, birds, cattle, every kind of "creeping thing," and,
finally, man and woman. Then he rested.
This infrared image from NASA’s Spitzer Space Telescope shows hundreds of thousands of stars crowded into the swirling core of our spiral milky way galaxy.
NASA Jet Propulsion Laboratory California Institute of Technology
In thinking about this story, notice that God first made the entire physical and
natural environment, everything from the stars to green grass, then fashioned human
beings and put them into this setting. In the creation story that modern science tells,
the environment was also created before humans, but the time scales are very different.
According to modern science, humans evolved on a planet that had already existed for
over four-and-a-half billion years. The terrestrial environment shaped the creation of
our species. Moreover, the environment of the earth was itself the product of the earlier
history of the cosmos as a whole. Consequently, in introducing Big Era One we must
begin at the beginning, setting the debut of Homo sapiens within the largest possible
scene in both time and space.
The Universe
Modern science suggests that the universe was created about 13.7 billion years
BP. What existed before that moment? At present, we have no way of answering that
question. Many astronomers would say that the query is meaningless because neither time
nor space existed before the creation of the universe. There was nothing. Even so, there
must have been at least the possibility of something, because in this "nothingness" a sort
of explosion occurred. Within a split second of that explosion, something did exist. The
early universe was tiny and fantastically hot, a searing cloud of energy and matter, much
hotter than the interior of the sun. For a trillionth of a second the universe expanded
faster than the speed of light, until it was bigger than an entire galaxy. Then the rate of
expansion slowed, though expansion continues to the present day.
The solar system is depicted at the bottom of this famous NASA
plaque mounted on 1972’s Pioneer spacecraft, carrying a message
to potential extraterrestrials. The arrow at the bottom indicates the
spacecraft’s trajectory through the planets. Other symbols include
naked, friendly humans, neutral hydrogen, and the relative position
of the sun to the center of the galaxy.
NASA. Wikimedia Commons
As the universe expanded, it cooled down. After about 300,000 years, it was cool
enough that protons and electrons could combine to form atoms of hydrogen and helium.
These are the simplest atoms of
all. After about one billion
years, huge clouds of hydrogen
and helium began to collapse in
on themselves. As they did so,
their centers got hotter and
hotter. When they were hot
enough, hydrogen atoms began
to fuse together violently like
vast hydrogen bombs. In this
way, the first stars lit up.
Hundreds of billions of stars
appeared, gathered in hundreds
of billions of clusters that we call
"galaxies." In the stars, new
chemical elements were created,
so that as stars lived and died,
they generated the energy and
raw materials needed to make new and more complex types of matter. So it is no accident
that complex objects such as planets and human beings appear near stars.
Our Galaxy
Our attention now turns to one tiny part of the universe. Our sun and the planets that
circle around it were created about 4.5 billion years BP, so they are about one third of the
age of the universe. They were created about two thirds of the way from the center of a
galaxy we call the "Milky Way." Look up at the heavens on a clear night, and the Milky
Way looks like a pale creamy pathway through the stars.
Our sun is a star, and like all other stars, it was formed from the collapse of a huge
cloud of gas and dust particles. More than 99 percent of this material went to make up
the sun, but wisps of matter orbited around it at various distances. Over time, the matter
in each orbit was drawn together by gravity or by violent collisions into lumps of matter
that eventually formed the planets. This is how our earth was formed. At first, it was
extremely hot. The heavy metals within it melted and sank to the center of the earth to
form its core. Lighter materials rose to the surface, and gases bubbled up to form the
earliest atmosphere.
The Earth
The early earth was a violent place, bombarded by asteroids, and bubbling with
heat from its interior. If you visited its surface, you would have seen landscapes full of
volcanoes. But you would not have been able to breathe because its atmosphere contained
no oxygen. Slowly, the number of asteroid impacts diminished, the surface cooled, and,
about 4 billion years BP, water vapor in the atmosphere condensed to form the first oceans.
This 2002 scanning electron micrograph (SEM) shows an amoeba in its trophozite phase, a vegetative period spent feeding, moving about, and reproducing.
Wikimedia Commons
Eventually, the earth’s surface hardened and congealed, forming a number of thin
plates that floated on the hot, molten material beneath. These plates slowly moved around
the surface, and where they collided, they formed huge mountain chains. Where they
moved apart, they created huge tears in the
earth’s surface. You can see one of these
tears in Africa’s Rift Valley. Some of these
huge valleys eventually filled up to form new
oceans. This process, known to geologists as
"plate tectonics," means that the surface of
the earth has changed continuously. As it
changed so did the landscapes and weather
patterns at the surface of the earth.
Early Life Forms
Life evolved in this ever-changing environment. The first living organisms probably
evolved deep within the seas. Around volcanic vents at the bottom of oceans, complex
chemicals engaged in ever-changing reactions powered by the heat from these volcanoes.
Those reactions led to the formation of complex chemicals that eventually created the first
living organisms. Did life evolve only on our earth? At present, we do not know for sure.
It seems likely, however, that life has evolved many times, wherever planets appeared that
are similar to our earth.
The earliest living organisms consisted of single cells, as most living organisms do even
today. The earliest organisms probably fed off the chemicals leaking from deep-sea
volcanoes. Their fossil remains can be
identified today, and the oldest of these
remains can be dated to about 3.5 billion
years BP. Like all living organisms, those
early single-celled creatures were subject to
the laws of evolution. Minor changes in
organisms were passed on from generation
to generation. Those organisms that
flourished best in particular environments
multiplied most successfully and left the
most descendants. In this way, generation
by generation, the average features of
species gradually changed and diversified, eventually forming entirely new species. And the
number and variety of different species increased.
Homo erectus skull
Naturmuseum Freiburg Wikimedia Commons
By as early as 3.5 billion years BP, some single-celled organisms began to derive energy directly
from sunlight by using the chemical reaction
known as photosynthesis. Since then, the sun’s
energy has been the main "battery" driving life
on earth. Photosynthesizing organisms breathed
in carbon dioxide and breathed out oxygen.
So, as they multiplied, the amount of oxygen
in the atmosphere increased. Living organisms
were already shaping the earth’s atmosphere.
Eventually, more complicated cells appeared that
could "breathe" oxygen. These are known as "eukaryotic" cells. From about 600 million
years BP, organisms appeared that were made up of many individual eukaryotic cells.
These were the first "multi-celled" organisms. Large, multi-celled organisms eventually
colonized the land, in the form of plants, fungi, and animals.
Animals
One hundred million years BP, the most flourishing land-based animals were the
reptiles we call dinosaurs. About 65 million years BP, however, most of them died off in
what was probably a catastrophic meteor impact. Now other types of large animals could
flourish in their place. Most successful of all in the last 65 million years has been the
large class of animals called
mammals. These are warm-blooded, fur-bearing animals that
nourish their young in their mothers’ wombs and feed their infants with mother’s milk.
After the dinosaur calamity, mammals began to spread, multiply, and diversify, occupying
many of the
niches once inhabited by dinosaurs. There appeared grass-eaters, meat-eaters,
swimming mammals such as whales, and even flying mammals such as bats.
Our hominin ancestors used tools known as Acheulean hand axes from about 1.4 million years BP.
This specimen was found in France. What useful tasks might an individual have been able to perform with this axe?
Kathleen Cohen World Images
One family of mammals, the
primates, were specialist tree-dwellers. To survive in
trees they needed good 3-D vision and a brain large enough to process a lot of visual
information. They also needed hands that could grip things with precision. Our own
ancestors, the
hominins, belonged to a branch of the "great apes," a group of primates
that had learned to live at least part of the time on the ground. The first hominins (a term
replacing the older word "hominid") appeared about six million
years BP, in Africa. What distinguished the first hominins
from other great apes was that they could stand upright.
Their brains, however, were about the size of those of
modern chimpanzees. In Africa, hominins flourished,
alongside many other species, and in time a great
variety of different hominin species appeared.
Humans and Other Humans
Early hominins probably lived much like modern chimpanzees or gorillas, that is,
in small, family-sized groups that gathered most of their food from plants but also ate
insects and small animals. They also occasionally scavenged the meat of larger animals.
From about two million years BP, some hominins, from the species known as
Homo erectus,
migrated out of Africa along the warmer southern fringe of the Eurasian
landmass from Europe to China. During the next two million years, new species
of hominins appeared in this huge
region, some with larger brains. One of
those species, known as
Neanderthals,
flourished in the last 500,000 years.
How did our hominin ancestors live?
Like chimpanzees and gorillas, our closest
relatives, they were highly social animals
that lived in family groups probably
ranging from five or six to thirty or forty
individuals. We can be pretty sure that
they were smart, because chimpanzees are smart. We know they could use and make stone
tools because we have found remains of those tools dating from about three million years
BP. Modern attempts to make stone tools show how hard the work is, but they also show
that using them could make quite a difference to the diets of early hominins. With sharp
stone flakes, you could butcher the remains of a large animal very efficiently—as long as the
other scavengers, such as hyenas, left you in peace. Using sharpened sticks, maybe hardened
in a fire, you could also get at roots of plants. Some early hominins may have used fire. We
have strong evidence for the use of fire by hominins living in China in 500,000 BP. Some
evidence from Africa suggests that hominins were using fire even earlier than that.
We can also be reasonably sure that early hominin societies were quite complex.
Studies of chimpanzee groups today show that they compete for status, making complex
alliances with one another to achieve higher standing. Politics of this kind require a lot
of "political" intelligence. We also know that chimps care for each other. Mothers have
much care for their offspring, and they appear genuinely distraught if their babies come to
harm. Hominins almost certainly engaged in behaviors that were equally complex.
Humans and Ideas
A varied stone tool kit, elemental social organization, and the control of fire all
enabled Homo erectus to become a well-traveled species, one successfully adapted to
a large part of the world. Even so, there is still something alien about this creature.
Despite its likely successes at social cooperation and competition on a small scale, it
did not, as far as we know, evolve complex rules for sharing food, resolving conflicts,
or strategizing long-term survival. Homo erectus fossil and tool sites have so far turned
up no evidence that they knew anything of symbolic expression, religion, art, or even
how to build a simple fireplace. As far as we know, this species produced no wall
paintings, no stone carvings, no intentional burial of the dead. In fact, their lifeways
changed remarkably little in the two million or more years that they survived, certainly
compared to the changes human society has undergone in the past several millennia. The
evolutionary processes that produced Homo sapiens, the "wise human" (a name we have
given ourselves!), involved not only anatomical changes and greater tool-making skills
but also the emergence of social communities that consciously shared a life of symbols,
ceremonies, and aesthetic expression.
We may ask, then, why was it that the history of early hominins, like that of
chimpanzees, was so different from that of our own species of hominin? Why did these
earlier hominins remain confined to Africa and the southern part of Eurasia, never
adapting to colder, northerly regions and never reaching Australia or the Americas?
Why did they never build villages or cities? Why are chimps still living in roughly the
same parts of Africa where their ancestors lived two or three million years BP, and why
have their numbers probably remained roughly the same throughout that entire period?
Why, by contrast, did Homo sapiens occupy all the great landmasses excepting Antarctica
and grow to number more than 6 billion today, living in the vast communities we call
cities? In short, what is so different about our own species of hominins? We will take up
that question in Big Era 2.
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