Timescales Summary


Time Scale 1

13.7 billion to 1 billion years ago

This is an image of some of the farthest galaxies ever seen from a time when the universe was about 400 million years old. Using NASA’s Hubble Space Telescope, the image shows some of the first galaxies that were formed shortly after the big bang occured.

Credit: Photo by NASA/ESA/S. Beckwith(STScI) and The HUDF Team, Courtesy of NASA

How did the universe come to be? When did this happen? For most of us, the processes that created the universe are so foreign and bizarre to our everyday experiences that they stretch our imaginations to their limits. Physics, astronomy, and mathematics have provided most of the evidence for the story of our cosmic genesis.

The story begins some 13.7 billion years ago with the “Big Bang”, where the entire contents of the universe emerged from nothingness. Exactly how and why this came to be is not known. Our universe is believed to have been originally compressed into a single point smaller than the size of an atom, a point of unimaginable heat and density. Matter, energy, time, and space were created in that first millisecond of the “Big Bang”. This was followed by a rapid expansion of the universe, a primordial, cosmic plasma “soup” in which a battle ensued between matter and antimatter particles annihilating each other into oblivion. A small amount of that matter won out, and makes up the ‘stuff’ of the world we know.

Over the course of billions of years, as the very early universe continued to expand and cool, new components of the universe appeared in sequence: subatomic particles, simple atoms (e.g. helium and hydrogen), clouds of gas (nebulae), and then stars. Gravity continued to cluster stars into galaxies, and hypernovae explosions produced heavier elements, scattering them through the universe.

Among the trillions of stars that formed, an enormous grouping of over 200 billion stars formed, our Milky Way galaxy. One star on an outer arm of the Milky Way is our sun. As our sun coalesced from its solar nebula about 4.6 billion years ago, the planets of our solar system -including the earth – began to form from the accumulation of gas and dust into small particles. Around 4.5 billion years ago, the early earth was catastrophically struck by a Mars-sized planet – tilting the earth on its axis, and, from the debris, creating the moon.

During the next several hundred million years, the earth developed its liquid oceans, rocky continents, and a primitive, oxygen-poor atmosphere. Out of these conditions the earliest life emerged, almost certainly in the oceans. The earliest life forms were simple, single-celled organisms with DNA that could reproduce. By 3.5 billion years ago, cyanobacteria, simple life forms without a nucleus, were producing oxygen through photosynthesis, converting our atmosphere to one that ultimately supported more complex life, including cells with a nucleus and, ultimately, sexual reproduction.


Time Scale 2

1 billion to 100 million years ago

Prehistoric Life Pageant
“The March of Life.” The progression of life from a “primordial soup” to more and more complex life forms over time.

Credit: Illustration by John Sibbick, courtesy of John Sibbick Illustration. This illustration is used with permission. All rights reserved.

How did the design of animal body plans emerge during the course of evolution? During Time Scale Two, the first complex animal forms emerge from worm-like ancestors. After a number of extreme ice ages, the last “Snowball Earth” phase occurred about 635 million years ago. The subsequent warm period may have created favorable conditions in the sea leading to the “Cambrian Explosion,” which occurred about 540 million years ago. All of the modern animal groups emerge at this time, including annelids (worms), jellyfish and anemones, sponges, brachiopods (“lamp shells”), bryozoans (“moss animals” or “sea mats”), mollusks (snails, clams, squid, octopi), arthropods (crabs, spiders, insects), and chordates (our ancestors), and the major developments leading to the emergence of the dinosaurs and early mammals are documented in the fossil record.

The major stages of animal evolution that emerge during this period include chordates, vertebrates, jawless fishes, jawed fishes, lungfish, amphibians, reptiles, mammal-like reptiles, and finally mammals. The greatest extinction event in the history of life, the Permian Extinction, occurred around 250 million years ago, with over 90 percent of the earth’s species going extinct.

During this Time Scale the first land plants also populate the continents, and the African plate separated from the North American plate (creating the Atlantic Ocean). The earth was populated with the major groups (phyla) of animals we know today, although the fossil record preserves earlier, ancestral forms for these animal groups.


Time Scale 3

100 million to 10 million years ago

Cretaceous Impact
About 65 million years ago, an extraterrestrial impact wreaked havoc on earth’s life forms. The vestiges of the catastrophe are recorded in the geological strata that is known as the Cretaceous-Tertiary Boundary.

Credit: Illustration by Don Davis, courtesy of NASA

How did mammals and birds come to replace the reptilian dinosaurs as the major inheritors of the earth? The later evolution of the dinosaurs occurred between 100 and 65 million years ago, including such forms as Tyrannosaurus rex and Velociraptor as well as the three-horned Triceratops.

It now appears that 65 million years ago the earth was struck by a large extraterrestrial body (an asteroid or comet) about 5 miles in diameter, about the size of Mt. Everest). This catastrophic impact (now known from a 100 mile-wide crater off the coast of Yucatan, Mexico) would have created a 5 mile-high tidal wave in coastal areas, reaching far into the continents and flooding much of the land. This was followed by a firestorm of countless rock fragments launched into space only to re-enter the earth’s atmosphere as fireballs heating much of the earth to oven-like temperatures. The massive quantities of dust particles created by the impact circled the earth and probably then caused a cold, dark “nuclear winter”, in which much of the earth’s plant life would have perished, starving many of the surviving animals that would have fed on them. Talk about being in the wrong place at the wrong time! Geologically, the strata documenting this catastrophe have been called the “K-T” or Cretaceous-Tertiary Boundary.

About two-thirds of the existing species perished and are not found in the fossil record after this event (that is, above the K-T Boundary), including all of the dinosaurs. This apparently opened vast niches for mammals and birds, as well as a host of other animals, and created conditions for the rapid spread and diversification of new forms. The major orders of mammals emerged during this time, including marsupials (kangaroos, platypus, etc.), insectivores (moles, shrews, hedgehogs), lagomorphs (hares and rabbits), carnivores (dogs, cats, hyenas, bears, raccoons, skunks, otters, etc), rodents (mice, rats, chipmunks, squirrels, hamsters, gerbils, etc.), bats, sea mammals (whales and dolphins), artiodactyls (even-toed giraffes, deer, antelope, cattle, sheep and goats, pigs, hippos, and camels), perissodactyls (odd-toed animals including rhinos, horses, and tapirs), edentates (armadillos, sloths, and anteaters), and hyraxes and dassies. The first representatives of our order, the primates, emerged during this time. The fossil primate record documents the evolution of the first prosimians, monkeys, and apes over the following tens of millions of years.


Time Scale 4

10 million to 1 million years ago

Early bipedal ancestors. Australopithecus africanus from Sterkfontein Cave, South Africa ca. 2.5 million years ago, an example of a small-brained bipedal hominin.

Credit: Photo by Kathy Schick, courtesy of the Stone Age Institute. All rights reserved.

How did our ape-like ancestors come to be human? This time scale documents the transition from our ape-like ancestors to the earliest bipedal hominids. The earlier parts of this story occurred on the African continent during a time of climatic fluctuation and a general cooling and drying phase. By five million years ago human ancestors were walking upright but still had small, ape-like brains. By two-and-a-half million years ago, two major hominid branches had emerged: the smaller-brained, larger-toothed robust australopithecines (destined for extinction), and the larger-brained ancestors of what would become ourselves, modern humans.

The first recognizable stone tools and cut-marked animal bones emerge about two-and-a-half million years ago as well. The earliest documented human technology consists of battered pebbles that were used to flake stone as well as to crack open animal bones, and flaked cobble-cores and the resultant flakes and fragments struck off of them. Cut-marks and percussion fracture marks on animal bones indicate that tool-using hominids were butchering a range of smaller and larger animals and feeding on the meat and marrow. Technology could have also been used to shape and sharpen sticks for digging up edible roots and tubers and for making containers for carrying plant foods and other materials. These earliest technologies (called the “Oldowan” after the famous site of Olduvai Gorge in Tanzania) are contempory with smaller-brained australopithecines, Australopithecus garhi in East Africa and Australopithecus africanus in South Africa. These hominids had brains about one-third the size of modern humans.

By around two million years ago, human ancestors were developing larger brains and smaller jaws and teeth, probably with the habitual use of stone tools and other material culture and technology. Quite likely a feedback system was co-evolving between biology, on one hand, and technology and culture on the other. The earliest forms of our own genus, Homo rudolfensis and Homo habilis, emerged at this time, hominids with larger brains, about one-half the size of that of modern humans. By 1.8 million years ago, humans had spread from Africa to Eurasia.

A new hominid form, Homo erectus, emerged about 1.7 million years ago. This human ancestor had a brain about two-thirds the size of that of a modern human, and similar body proportions and size to modern humans as well. With the emergence of Homo erectus all other major hominid forms, including the robust australopithecines, appear to go extinct. Coinciding with the emergence of this new hominid form is a new technology, called the “Acheulean”, characterized by large cutting tools, handaxes and cleavers, made on large flakes struck from boulder-cores.


Time Scale 5

1 million to 100,000 years ago

Homo heidelbergensis
Almost human. Cranium of Homo heidelbergensis from Broken Hill Cave, Zambia ca. 500,000 years ago. These large-brained forms coould make beautiful handaxes and other tools.

Credit: Photo by Kathy Schick, courtesy of the Stone Age Institute. All rights reserved.

This time period documents the spread of Homo erectus and their descendants through much of the Old World, and the first appearance of our species, Homo sapiens or anatomically modern humans, in Africa. A sister species found at this time in Europe and the Near East was Homo neandertalensis or “Neandertal Man,” which was contemporary with modern humans during the later range of this time period. It also appears that surviving populations of Homo erectus may have existed in East Asia throughout much of this period.

There are a number of new innovations that emerge in the prehistoric record at this time – more symmetrical and refined handaxes and cleavers, the first antler and bone soft hammers for delicate flaking of stone, the first known wooden spears (and probably more habitual hunting of larger game), possibly early ritualistic behavior, and by the end of this Time Scale, the widespread controlled use of fire. There is a slow shift from the Acheulean handaxe and cleaver technologies to technologies stressing smaller flake tools, some with prepared core strategies for producing special types of flakes, that are characteristic of the Middle Palaeolithic or Middle Stone Age.

Over this period of this time, our ancestors evolved much larger brains, settled in many tropical and temperate areas of Europe and Asia. Adaptation to cooler climates is unusual in primates, and these hominins probably used material culture (e.g. hides for clothing and blankets, fire) to adapt to these new conditions.


Time Scale 6

100,000 to 10,000 years ago


Horse Painting at Lascaux Cave, France
This is an image of a cave painting of a horse in Lascaux cave, France. Paintings of animals may be found throughout the cave, and may have been created about 17,000 years ago.

Credit: Photo by Courtesy of Wikipedia

When did humans begin to communicate with symbols? What is the earliest archaeological evidence for language, art, music, and religion? What do the earliest forms of recognizable human architecture look like? Glimmerings of modern human behavior can be found in Africa about 80,000 years ago in the form of bead jewelry and geometric art, and over the next seventy millennia a wide range of human societies develop profound innovations in terms of their tools and technology and their artistic and symbolic expression.

It is during this time period that anatomically modern people first colonized Australia (then joined to New Guinea and Tasmania to form the continent called Sahul), and the Americas. New technological traits that emerge during this time include bone and antler tools (points, harpoons, needles – and presumably sewn clothing), spear throwers (atlatls), stone lamps, ceramics and pottery, art (in the form of cave drawings and paintings, engravings, sculpture), musical instruments, and the bow and arrow. The first definite architectural structures are also known from this time period.

This period ends with the demise of the last Ice Age between 12,000 and 10,000 years ago, with warming conditions causing sea levels to rise worldwide and ultimately produce the coastlines that we are familiar with today.


Time Scale 7

10,000 to 1,000 years ago


Pyramids at Giza, Egypt
The pyramids in Giza, Egypt were built by separate pharaohs. The oldest and the largest of these pyramids is the Great Pyramid built by Pharaoh Khufu during the 4th Dynasty period, about 4,500 years ago. It is considered to be one of the oldest of the Seven Wonders of the World, and is the only one that is still in relatively good condition.

Credit: Photo by Ricardo Liberato, Courtesy of Wikipedia

How did early humans learn to domesticate plants and animals? What were the conditions that led to the independent rise of civilizations in the Near East, East Asia, Africa, and the Americas? How did the potential accumulation of wealth and power give rise to more socially stratified societies? How did technologies and lifestyles change with the rise of metallurgy?

This time period documents the slow transition from hunter-gatherer bands to early pastoralists and agriculturalists. With a more productive and reliable food base, populations grew and villages flourished. As farming spread in both the Old World and the New World, new innovations and technologies also spread: ground stone axes, pottery, grinding stones for processing cereal crops, shrines, and, eventually, the monumental architecture.

Then, in many parts of the world these give rise to the emergence of more complex urban societies, sometimes called “civilization.” The earliest evidence for cities, writing systems, metallurgy (copper, then bronze, then iron), wheeled vehicles, and horse transport are found during this period, as well as the first large-scale ships and early experiments in democracy.


Time Scale 8

1,000 to 100 years ago

Galileo Galilei was a an Italian mathematician, physicist, astronomer, and philosopher who lived in the late 15th century. He is credited with improving the telescope and is considered to be the father of modern science. He was a staunch supporter of Copernicanism.
Credit: Illustration by Courtesy of NASA.

This time period documents the development of develop the scientific method and the launching of the industrial revolution. This time period documents the rise of firearms in warfare, changing the ways that military strategy was planned and executed. It witnesses the flowering of painting, sculpture, literature and architecture of the Renaissance. During this period the printing press with movable type revolutionized the dissemination of ideas on parchment and paper. It saw the Ages of Exploration and the European discovery of the Americas, Australia, and the Pacific Islands (and exploitation of indigenous peoples and resources in far flung areas of the world). Significantly, powered transport on the sea, the land, and finally the air developed during this period, bringing different peoples in the world into closer contact and at an accelerating pace.

Most importantly, it was during this period that the scientific method truly flourished, emphasizing empirical evidence, careful observation and recording, and experimentation. Advances in astronomy (facilitated by the use of the telescope), biology (facilitated with the use of the microscope), physics, chemistry, engineering, geology, palaeontology, and archaeology were all products of this Scientific Revolution. Darwin’s concept of evolution by natural selection, showing that life forms changed over time as they adapted to changing conditions, became the pillar of the life sciences and became increasingly well-demonstrated and documented by the prehistoric fossil record.

The Industrial Revolution saw the rise of steam-generated power, standardization, and interchangeable parts, as well as profound socio-economic changes (not all of them good). Steam engines and, later, the internal combustion engine revolutionized human transport and trade in the form of trains, ships, automobiles, and finally the first airplanes. Electricity provided the energy required to illuminate entire cities. New ways of recording and documenting the world included photography, cinematography, and the phonograph, and new ways of long-distance communication included the telegraph, telephone, and radio.


Time Scale 9

100 to 10 years ago

Apollo 16 Lunar Landing, 1972
This photo was taken on April 20, 1972 during the Apollo 16 lunar landing mission. Lunar module pilot Charles M. Duke, Jr., took this photo of astronaut John W. Young, commander of the mission, saluting the U.S. flag during an extravehicular exercise.
Credit: Photo by Charles M. Duke Jr.,
Courtesy of NASA.

What are the most important human achievements of the last century? Our understanding of the nature of the universe, the strange laws of space-time physics, and the structure of the code of life (DNA) and how it replicates were major discoveries of this time period.

Technological innovations included rockets and jets, spacecraft, television, computers made with transistors and silicon chips, the beginnings of the World Wide Web, antibiotics and unique medical devices, and the harnessing of the atom for war and peace. High technology (personal computers, cell phones, GPS, etc.), became an ever-increasing part of a person’s lifestyle and in an ever-expanding wave around the world. Air transportation could shuttle a person anywhere in the world in less than a day. Satellites were employed for telecommunications, weather forecasts, and surveillance.

Human societies became ever-more dependent on hydrocarbons (coal, petroleum, natural gas) for energy production for power plants, houses, cars, planes, and ships, creating changes in the earth’s atmosphere in the form of increased carbon dioxide. Genetics and molecular biology were used as tools to study evolutionary relationships.

If you are reading this, you were probably born during this Time Scale. Never before had science, technology, and communications developed and spread so rapidly. High-tech devices that were cutting edge a few years previously could now become quickly and completely outmoded. We now live in a Brave New World…


Time Scale 10

The last 10 years

Wind Park in Galicia, Spain
This is a windpark in Galicia, Spain. In 2010, windpower produced 16% of Spain’s energy needs. Spain is the fourth largest wind energy producer in the world, following the United States, Germany, and China.

Credit: Photo by Arnejohs, Courtesy of Wikipedia.

What are the most important human developments of the past decade? This question is almost certainly going to provoke argument and contention, since different people might have widely different ideas about what is most “important.” And our calculations of importance may factor in, to varying degrees, perceived impact on our lives now, in the current day, as well as forecasts of potential mid-range or long-range effects on human populations and on the rest of our ecosystem, including other organisms (plants, animals, etc.), the earth’s atmosphere, oceans and water supplies, climate and weather systems, and overall resources.

Many important developments were actually refinements or new applications of older technologies. Satellite technologies allow you to pinpoint your exact location on the earth, and new imaging techniques allow you to zoom in on your house from space. Music is downloadable, with a pocket-sized player holding thousands of songs. Technologies trying to free us from the tyranny of petroleum dependence in our energy needs are being developed. We have now mapped the human genome, and we are exploring other planets and other moons in our solar system. And, after years of debate and controversy, there is growing consensus that our emissions of carbon dioxide from fossil fuels are creating a serious global warming over time.

This list of these events is intended to be controversial; it is likely that many of you would pick some different things than we did.

This time period sets the stage for our future destiny as a species and for the destiny of the rest of the planet.

Comments are closed.