Lucy’s Cradle (fisheye)

For as long as humans
have walked the Earth, we’ve contemplated the
starry night sky, seeking to understand the connection
between the heavens and ourselves. Today modern tools like
the Hubble Space Telescope provide us with a view of the universe
unparalleled in human history. Our vision now extends into
the farthest regions of space and to the earliest moments of time. We wonder why we’ve found
life only on Earth and when our ancestors first
became aware of the universe. To understand why some worlds bear life, we will visit the barren worlds
in our solar system. To discover when life became intelligent, we will journey to the grasslands
of East Africa over three million years ago. Over a hundred planets and moons
of all sizes orbit the Sun, yet only one has intelligent life or perhaps any life at all. Many of the outer planets, like Saturn, lie so far from the Sun that the Sun looks like
a bright star in their cold eternal night. These are frozen worlds without
enough energy from sunlight to fuel the birth of life. Distance from the Sun is the first critical factor in
the development of life. Solar energy increases as we move
sunward toward Jupiter. This is a world that produces
its own energy by shrinking – generating heat as gravity
reduces its size. Turbulent windstorms race through
the cloud tops at hurricane speeds, creating bright zones and dark
belts in Jupiter’s atmosphere. Life is most unlikely in this violent toxic floating world without a solid surface. But Jupiter’s large moons could harbor life. For instance, Io, closest of the large moons, is an amazing world of dramatic change. Its surface is always active
with erupting volcanoes that constantly resurface the moon. But on Io, change is too
violent and destructive, and the surface is too unstable
for life to develop. Callisto possesses the most ancient surface. With highly eroded canyons and ice valleys, this world has changed very little
since its birth billions of years ago. Although violence destroys life, life cannot develop and evolve
on a world without any change. The barren Callisto is as poorly
suited for life as the violent Io. Jupiter’s moon Europa looks more like a cracked ice ball than a moon. It is a much less violent place than Io, but much more dynamic than Callisto. On its surface, long fissures mark
fracture lines in the icy crust. Underneath could be a liquid
ocean and possibly life. Jupiter’s moon Ganymede
also has an icy crust. On Europa and Ganymede, water provides the medium and tidal forces with Jupiter
could provide the energy. But any life below these icy surfaces would certainly be simple and primitive. The necessary conditions are present, but they cannot guarantee the emergence of life. Moving sunward we reach the red planet Mars. Although just half the size of Earth, Mars is a world of gigantic features like volcanoes larger than Mt. Everest, canyons the width of the United States, and ancient dried up riverbeds. Billions of years ago this world was much wetter
with a thicker atmosphere that allowed liquid water on its surface. Life could have begun here long ago, but today’s dry and cold Mars cannot
support the development of life. Any life on Mars now hides below the planet’s parched surface. The Martian atmosphere is too
thin to support life, but what about the much
thicker atmosphere of Venus? Venus has sometimes been
called Earth’s sister world. But a closer look by Russian landers reveals a nightmarish planet
of intense pressures, extreme temperatures,
and sulfuric acid rain. This is a world of the right size
and distance from the Sun for life. Yet its atmosphere is poisonous, and its surface too hot
and oppressive for life to form. The RIGHT atmosphere is
also critical for life. At last we approach the third planet, Earth, covered with fertile land
and life-bearing oceans. Solar energy, atmosphere, liquid water,
and moderate temperatures – all are here for the development of life. On Earth, life not only exists, but also has become intelligent and
aware of its place in the universe. Once life appeared in the oceans of Earth, what conditions caused it to develop
into organisms of many cells, complex designs, and eventually, self-awareness? On Earth, the changing environment forces life to adapt or die. The most dramatic changes affecting life on Earth may have come from space. In 1994, a fractured comet plunged into Jupiter, releasing the energy of a thousand atom bombs. Any one of the comet’s twenty fragments
could have caused major damage on Earth, but Jupiter’s gravity captured this comet, thus protecting the inner solar system. Development of life,
especially intelligent life, may require a planet like Jupiter to protect
inner planets from devastating impacts. Earth’s last great impact
occurred 65 million years ago. A 10-kilometer wide asteroid slammed into
the southern Gulf of Mexico. Its fiery plunge created temperatures
hotter than the Sun’s surface. Soot and floating ash could have
blotted out the Sun for months, possibly years. Dominant animals, like the Triceratops
and Tyrannosaurus rex, could not adapt to the drop in
temperature and loss of food supply. Up to 70% of all species perished, including all of the non-flying dinosaurs. Afterward, the smaller mammals
adapted to the new environments, claimed the land that had belonged to
the giant reptiles, and flourished. But where on the planet
would intelligence appear? And When? What conditions would create
the cradle of humanity? Today Homo sapiens sapiens
is a worldwide species. Lights of human civilization cover
the modern globe, showing humans living in all
climates and conditions. The spread of modern civilization provides few clues about when and
where humans first appeared. The answer may lie in a special molecule found in the nucleus of human cells. Humans are all one species sharing 99.9% of the same genetic code, written in this long strand molecule called DNA. Three billion chemical building
blocks called bases form the rungs of this DNA ladder. The chemical structure of these 3 billion bases is almost identical in every human of
every race on every continent. Only about 3% of these bases actually
determine our characteristics. The remaining sequences are
never used by our cells, but help us track the migration of
humans over the planet. These colored bars represent the
base pairs in a DNA sequence. Small changes occur when a DNA strand replicates these
base pairs during cell division and when DNA is passed
from parents to children. With each generation, the number
of these differences increases. Human groups that have been together the longest show the most DNA differences
from person to person. Tribes of southern Africa have
the greatest genetic diversity and have therefore lived together the longest. The differences within the DNA of indigenous people in the middle East are much less. The genetic diversity is still lower in Europe, the Far East and Australia. The native tribes of North and South America have the fewest differences in their DNA. These variations in the
amount of genetic diversity show the migration pattern of humanity. The lineage of all modern humans can be
traced to a group of a few thousand adults living in East Africa, perhaps as recently as 60,000 years ago. Africa is a place of great geologic stability and of dramatic geologic change. It also contains the largest well-watered
tropical landmass on the planet. About 20 million years ago, East Africa’s Great Rift Valley began to form. This rift is an ocean being born, as land masses pull apart,
leaving a sinking basin behind. First the Arabian Peninsula
pulled away from Africa, creating a valley that soon filled
with water to make the Red Sea. The Afar Depression is a triple conjunction where the spreading ridges that are
forming the Red Sea and the Gulf of Aden emerge on land to meet the East African Rift. The Afar is slowly rifting apart
as earthquakes create fissures that lower and widen the valley floor. Over millions of years, the Red Sea
may erode through the highlands and flood this valley. In about 10 million years, the whole East African Rift could be submerged, forming a new sea as large as the Red Sea and leaving Africa without its horn. We are fortunate to be
excavating this cradle of humanity when tectonic rifting has revealed
so many buried early human fossils, but before these same forces
flood this area forever. On November 24, 1974, archeologists Donald Johanson and Tom Gray were mapping the Hadar site in the Afar Depression. After a morning of surveying, they spotted a forearm bone in a nearby gully. Soon they saw a fragment of the
skull bone and then a thighbone, some ribs, a pelvis, and a lower jaw. After two weeks of excavation, the team recovered several hundred fragments, representing 40% of a single skeleton
called Australopithecus afarensis. This fossil became the most famous inhabitant of the Ethiopian National Museum in Addis Ababa. The skeleton was named Lucy from the popular Beatles song –
“Lucy in the sky with Diamonds”. Ethiopians call the famous fossil Dinkenesh, meaning “you are wonderful”. A dramatic change in Earth’s global climate may have produced conditions that favored
the development of humans in East Africa. For most of geologic time, the world’s climate was warmer and
more stable than it is today. The Sahara Desert in North Africa was much greener and more fertile. But the climate became dryer and more seasonal when Antarctica drifted over the South Pole. Enormous ice sheets trapped
water from Earth’s oceans, leading to the dryer global climate. While Antarctica drifted over the South Pole, the North Pole was also in a state of change. Drifting continents in the northern hemisphere were gradually changing ocean circulation
patterns in this hemisphere as well. Over time, the Arctic Ocean became
almost land-locked at the North Pole. Continents and islands
surrounding the Arctic Ocean were also ice covered, trapping even more water. These Arctic and Antarctic conditions blocked the flow of warm water from
the equator to the poles and encouraged the accumulation
of ice at both poles. With the appearance of ice caps, global temperatures dropped and ice
periodically covered northern Europe. These ice ages brought drier and more
severe seasonal weather to the planet. In Africa, they caused many
tropical forests to become grasslands. At this time our distant ancestors
gradually left the trees and learned to thrive in the new open savannas. Lucy embodies these early human ancestors. She lived over three million years ago and was about the height and
weight of a young girl today. She was fully bipedal – walking
upright on two legs. By standing upright she could
look over the grassland, cover longer distances, spot predators, and regulate her body
temperature more efficiently. Because she walked on two legs,
she would probably have recognized the Sun, and the cycles of day and night – or at least
reacted to changes in light level. Lucy’s hands were humanlike but her
fingers were slightly more curved. Her brain was less then a third of
the size of a modern human brain. And she had an ape shaped head
with a forward thrusting jaw. Although she walked on two legs
with her hands free, there is no evidence that
she made or used stone tools. Based on the fossil record of East Africa, we can show the changing appearance
and environment of our human ancestors, beginning 5 million years ago. Our story starts with Ardipithecus
who walked upright, but probably made his home in shady forests, rather than open savannahs. Australopithecus afarensis appeared
almost 4 million years ago as the environment of East Africa was changing from tropical forest to open grassland. Lucy is an Australopithecus afarensis. She could retreat to the trees
to protect her young, but walking upright helped her gather food and avoid predators on the open plains. Australopithecus garhi lived less
than three million years ago. He was taller than Lucy, but had her
protruding ape-like face. Crude stone tools discovered nearby suggest that he might have been
a scavenger who could butcher meat, providing a diet rich in protein and fats. Homo habilis,
the first species of the Homo genus, lived about two million years ago. His jaw was less protruding and
his increased brain capacity was about half that of a modern human’s. Homo habilis was probably both
a scavenger and a hunter whose larger brain enabled him to track
the flights of vultures toward an animal carcass or follow the triumphant laughs
of a feeding hyena. Paranthropus boisei lived at
the same time as Homo habilis, but was much more muscled and had massive teeth designed for chewing grubs and hard-shelled nuts. His restricted diet may have led to his extinction while early humans thrived on
a variety of plants and animals. The very adaptable Homo erectus had a brain about 75% of a modern human’s. Mastering fire, he could also
tolerate colder temperatures and cook a variety of foods. His complex social group
required some form of language to communicate feelings and expectations. The first modern human,
called Homo sapiens idaltu, lived 200,000 years ago, along with hippos and buffalos, which he hunted and killed
using advanced stone tools made from volcanic rocks and glasses. These early humans may have had funeral rituals using fire to cremate their dead. Fossils found in East Africa, have allowed modern Homo sapiens sapiens to piece together an ancestry shaped by adaptation to a dramatically changing environment – a condition that favored
the development of intelligence, problem solving, communication, and community. About 74,000 years ago, a mega-colossal
volcanic eruption, called the Toba Event, covered the Earth in ash, ejecting 2,000 times as much material as
the 1980 Mount St. Helens eruption. Ash and sulfuric acid, carried westward
by prevailing monsoon winds, destroyed life across India,
the middle east and northern Africa. The eruption lasted perhaps two weeks, but the resulting volcanic winter
significantly altered global climate for the next thousand years, causing both drought and famine. This eruption may have caused
a global human population crash with perhaps only a few thousand humans surviving. Under the severe environmental stress caused
by the cold and dark volcanic winter, the surviving humans had to develop
new levels of cooperation and greater technical skills and tools – skills of invention and collaboration that would eventually empower them to expand and dominate the planet. Sky myths and patterns show how surviving human
civilizations around the world have adapted to different environments and developed a heritage of legends and heroes. The oldest known star map is an image of a hunter scratched on
a mammoth tusk over 30,000 years ago. This figure with arms and legs outstretched is posed like the Western constellation Orion, including the hunter’s sword. The hunter Orion is also mentioned in
the Biblical texts of the Dead Sea Scrolls found in caves at Qumran on
the Dead Sea’s northern shore. Farming and settled civilizations led to regular observations of the sky. In Ethiopia, the ancient land of Lucy, farmers used the appearance of
specific stars in the Orion region to set their annual calendar. As agriculture became more efficient, there was time for science, religion, calendar making and watching the heavens. In the architecture of Ethiopia, we also find modern expressions
of the complex relationship between humans and the stars. Stone monoliths dominate Axum, the capital city of the ancient Axumite kingdom, over 2,000 years ago. These obelisks have a rectangular base
with a false door carved on one side. Elements like small windows and
disk patterns decorate the shaft. These obelisks were erected as funerary markers and their structure may symbolize
tower leading to heaven. Within the ancient city of Gondar in
the Ethiopian highlands, lies the 300-year-old
Debre Berhan Selassie Church, its name meaning
“Trinity at the Mountain of Light”. Two arched doors lead into
the rectangular sanctuary. Inside the faces of angels appear
in rows between the ceiling beams. They stare down with large eyes etched in kohl, a black substance Africans use
to darken their eyelids. A monk painted the interior of
this small sistine chapel. He gathered the colors for his
paintings from local rocks, soil, plants and the blood of animals. Each of his faces has a different expression and all eyes appear to follow you
around the room. Here the connection between the Earth
below and legends of the sky above is very real and personal. Modern astronomers search for a new relationship between humans and the universe beyond. They travel to mountaintop
observatories to explore the cosmos – looking far beyond constellation patterns – seeing farther with each larger telescope. They also watch the motions of stars for evidence of planets beyond our
solar system that could harbor life. These astronomers are continuing
a magnificent journey of human vision that began over 3 million years ago when a young female peered over
the grassland of East Africa and saw the distant horizon
beyond her fingertips.

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