If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

READ: An Introduction to Big History

The Big History story of the universe – and human’s place in it – is told from two perspectives that are outlined in this article. The first, from historian David Christian, is based on thresholds of increasing complexity. The second, from geologist Walter Alvarez, concentrates on four movements: the Cosmos, the Earth, Life, and Humanity.
The article below uses “Three Close Reads”. If you want to learn more about this strategy, click here.

First read: preview and skimming for gist

Before you read the article, you should skim it first. The skim should be very quick and give you the gist (general idea) of what the article is about. You should be looking at the title, author, headings, pictures, and opening sentences of paragraphs for the gist.

Second read: key ideas and understanding content

Now that you’ve skimmed the article, you should preview the questions you will be answering. These questions will help you get a better understanding of the concepts and arguments that are presented in the article. Keep in mind that when you read the article, it is a good idea to write down any vocab you see in the article that is unfamiliar to you.
By the end of the second close read, you should be able to answer the following questions:
  1. What does it mean to periodize history?
  2. What are origin stories? What makes Big History a unique kind of origin story, according to the author?
  3. What is a “threshold of increasing complexity?”
  4. How is David Christian’s narrative of Big History different from Walter Alvarez’s?
  5. How are David Christian and Walter Alvarez’s narratives of Big History similar?

Third read: evaluating and corroborating

Finally, here are some questions that will help you focus on why this article matters and how it connects to other content you’ve studied.
At the end of the third read, you should be able to respond to these questions:
  1. How might studying Big History support our learning in a world history course?
  2. Based on what you learned from the text, what do you think could be the next threshold of increasing complexity?
Now that you know what to look for, it’s time to read! Remember to return to these questions once you’ve finished reading.

An Introduction to Big History: Thresholds of Increasing Complexity or Four Movements?

Photo of the planet Earth taken from outer space.
By Bob Bain
The Big History story of the universe – and human’s place in it – is told from two perspectives that are outlined in this article. The first, from historian David Christian, is based on thresholds of increasing complexity. The second, from geologist Walter Alvarez, concentrates on four movements: the Cosmos, the Earth, Life, and Humanity.


In the Era 1 Overview, you read about how everything in the Universe has a history. Everyone and everything—from your great-great grandparents to a World War II battle—has a history story. There's a history of the planet and even a history of the entire cosmos. You also learned that you can understand how the history of Earth or the universe fits into your own life story. But it requires some scale switching. You must look at time and space from different perspectives. And in order to make sure a history is coherent, or that it fits together as a story, you need to periodize it. That's a fancy way of saying how historians divide or categorize history into distinct chunks of time or eras.
The Big History story of the universe—and human's place in it—has been told from many different perspectives. Two of those perspectives are outlined in this article. The first is based on thresholds of increasing complexity. This is how historian David Christian organized 13.8 billion years of history to fit into one course. The second concentrates on four movements. It's based on how geologist Walter Alvarez chose to arrange his Big History.

Thresholds of increasing complexity: David Christian's Big History

David Christian is a historian who teaches at Macquarie University in Australia. He has written books on such topics as vodka in Russia, inner Eurasia, and Big History. Dr. Christian has recognized the importance of the stories people tell and the ways these stories help connect us in meaningful ways. He focuses on how we are connected to each other and also to the world and Universe in which we live. Some of these stories are origin stories. They explain the beginnings of where we came from, where we are in the universe, and where we are going. Every culture, Dr. Christian explained, had such origin stories. They played crucial roles in providing meaning to people. Sharing stories with others helped illuminate where people and their communities fit in our powerful, vast, and beautiful universe.
There is no common, modern origin story that suits our global community of over seven billion people. But Christian claims one has been emerging over the last 50 years. It's an origin story he calls "Big History". This modern story is different from other origin stories in two crucial ways. First, it is not tied to one region or culture, but is a story for all of us. Second, it draws on the best collective, evidence-based understanding of the universe, the Earth, life, and of humanity that we have.
The "plot" of Christian's story centers around the idea that sometimes completely new and more complex phenomena comes into existence. These phenomena are more complex because they have more parts. These parts are arranged in an entirely new way than previous "things". In his book Maps of Time, Christian coined the term thresholds of increasing complexity. The term identifies times when significant new forms of complex phenomena emerged. It gives a chapter-like structure to his story. He and other Big Historians, such as Cynthia Stokes Brown and Craig Benjamin, identified eight such thresholds of increasing complexity. This narrative is what the Big History Project used to structure its course in Big History.
So, what's the story? And why does it matter to world history?
Image of a book cover that shows a satellite view of the world at night, taken from outer space. Each continent is dotted by city lights.
This story begins with the emergence of the universe with the Big Bang. Our understanding of this first threshold developed recently. The physicists and cosmologists among us figured out how to measure the distance other stars are from the Earth. To our surprise, we learned that stars are moving away from us. This indicates that the universe is expanding. Using logic, scientists reasoned that that our expanding universe once upon a time must have been smaller, and smaller, and smaller still. Finally, they theorized that there must have been a point when the expanding universe emerged. They called this emergence the Big Bang. The early universe contained only hydrogen and helium and the four basic forces: gravity, electromagnetism, the strong force, and the weak force.
Image of a timeline featuring the thresholds of increasing complexity discussed in Big History.
Quite a Big History, wouldn’t you agree?
While relatively simple, these early elements and forces were enough for more complex phenomena to emerge such as stars and galaxies (Threshold 2). Then, more complex and heavier elements emerged (Threshold 3). Eventually our Solar System and Earth (Threshold 4) emerged. Gravity is a central actor in making the universe more complex after the Big Bang since it draws objects together. Gravity compressed clouds of hydrogen gas that formed a few billion years after the Big Bang, a compression that created increasing heat and mass, until finally the first stars "lit" up. The heat within stars and the heat produced when stars explode create more complex and heavier elements by fusing atoms together. About 4.5 billion years ago our Sun, an average-sized star, formed as gravity compressed gases just as it does when creating other stars. And gravity acted on the left-over "stuff" from the formation of the Sun to create the other planets and moons in our solar system. One of those planets is our Earth, a rocky planet with a single moon, a moon that revolves around the Earth while the Earth revolves around the Sun.
Living organisms, life, is Threshold 5 in Christian's Big History story. How living organisms emerged from inanimate—non-living—objects, is still a mystery. But it is a great example of complex things emerging from less complex things. The first organisms were single-celled bacteria. Some of these bacteria emitted oxygen into the air helping to form the ozone layer that protects us from the harmful rays of the Sun. From these single- celled organisms more complex life evolved to give us the great diversity of organisms on Earth. Today we have organisms ranging from micro-organisms to plants to animals, and, of course, to us humans.
This story, thus far, is not only a story of how the universe became more complex. It is also the story of how we humans developed our understanding of events over 13.82 billion years ago at the beginning of time. It is the story of how our Earth formed 4.5 billion years ago, or the origin of elements, or evolution of life. It is quite an amazing story about our curiosity, our innovations, and our collective learning. It is not just a big story of the universe. It is a story of the change in human's understanding of the universe.
If we can understand the science of physical and natural forces around us, we can develop clearer pictures of the past, the present, and the future. For example, we have learned a lot about the way the Earth formed with its unique elements, minerals, climate, landforms, and even its Moon. This knowledge has limited or encouraged human actions and experiences. Historians have been able to use new scientific explanations and understandings of our physical and biological world to provide stronger understandings of the past and the present. This in turn has enabled us to think with more knowledge about our future.
Christian's last three thresholds of increasing complexity are the Emergence of Humans and Collective Learning (Threshold 6), the Emergence of Agriculture (Threshold 7), and the Emergence of Modernity and Use of Fossil Fuels (Threshold 8). These thresholds represent three major transformations in our collective human experiences. These are the transformations that we will discuss in much greater detail in the rest of the course. Indeed, the World History Project is an extended investigation into the complexity that emerged with human actions. Complexity increased as humans evolved a language that allowed them to share culture and learning. It increased as humans domesticated plants and animals. And humans have transformed the Earth over the past 200 years with our use of fossil fuels.
Students in the Big History Project can tell a story of big changes. Their story covers over 13.82 billion years of time and an infinite amount of space. Those students can place all these "threshold" changes on one timeline and then explain how our universe and our lives have grown more complex. And they can trace that growing complexity from the Big Bang to Stars to Elements to Earth to Life to Human's Collective Learning to Agriculture to our Modern Age.

Another Big History story: Walter Alvarez's improbable journey in four movements

Not all Big Historians use Christian's threshold of increasing complexity to structure their history. Indeed, not all Big Historians are even historians. For example, Walter Alvarez is a geologist who taught a course in Big History at the University of California at Berkeley. He has also written a Big History, A Most Improbable Journey: A Big History of our Planets and Ourselves. Unlike David Christian, he does not use thresholds. Instead, he structures his course and his Big History around four regimes: the Cosmos, Earth, Life, and Humanity. For Alvarez, a regime is an orderly system that has some regularity or has developed some continuities. In telling his Big History narrative, Alvarez moves through the regimes of the Cosmos, the Earth, Life, and Humanity. He describes the patterns and regularities of each, and the specifics within each regime that are important for our lives. For example, in thinking about the Earth, Alvarez discusses the "gifts" of the Earth for humans. These gifts include silicon, which he argues is the Earth's favorite element and ours. It has played a vital role in the types of tools we have created, beginning with our first stone tools. In the regime of the Cosmos, the continuous "gifts" of elements emerge from stars.
Image of a book cover featuring the title in large, bolded, uppercase print and a small picture of planet Earth in the middle.
Alvarez's Big History does not simply focus on the continuities consisting of regularities, trends, or cycles. He also sees rare events, contingencies, that lead to significant changes in history. Specifically, he sees changes that people could not have predicted long before they happened. Dr. Alvarez and his father discovered the contingency when a comet or asteroid wiped out the dinosaurs. This was an important contribution to our understanding of our own history. "We humans exist," Alvarez wrote, "only because of the extinction of the dinosaurs" (Alvarez, 183). Dinosaurs dominated the Earth, limiting both the size and diversity of our mammalian ancestors. But that changed when, as much evidence suggests, a huge comet or asteroid hit the Yucatan Peninsula of Mexico. This impact happened about 66 million years ago and wiped the dinosaurs out. This rare event enabled mammals to thrive in ways they could not while the dinosaurs dominated. Obviously, comets wiping out species are not regular or continuous events, but rather a rare event that altered history. Human life, then, was contingent or depended upon this very rare, and irregular occurrence. Such contingencies populate the regularities in Alvarez's story.
While Dr. Alvarez tells historical stories in presenting his Big History, he does not put the changes onto one timeline. Instead he treats each of the regimes as a separate but connected story, filled with details about the Cosmos, the Earth, Life, and Humanity. But it's also a story about the people who discovered the patterns and continuities that shaped and continue to shape our lives. It's a story about the people that discovered the laws of gravity and light and the elements that make up the Earth. His regimes seem to be nested and interconnected and might be seen like this:
Nested diagram shows “Humanity” nested within “Life”, which is nested within “Earth”, which is nested within the “Cosmos”.
Table 1: Dr. Alvarez’s regimes of history.
Like Christian's Big History, Walter Alvarez's version stresses similar important events such as the Big Bang or the formation of the Earth and life itself. And like Christian, his story is filled with wonder of what an amazing and improbable a journey it has been. He marvels at the path that has led to our place in this time, on this Earth, and in this universe. And like Christian, this Big History sets the stage for understanding the place on which the rest of human history takes place.
Overview over: We have argued that history comes in different shapes and sizes. We've also explained that historians use different scales of time and space. These different scales shape or frame their investigations and their courses, including the very biggest scales of time and space. Then, we began this investigation into world history, at the very biggest scales possible. We began billions and billions of years before there were humans or even the Earth. We used the two versions of history at the very largest scales—the biggest of history—to give you a picture of the context within which human history plays out.
What do you think? Is there value in knowing how the universe and the Earth formed? Or what stars contribute to our past, our present, and likely our future?
Does it make a difference if you tell this story using thresholds of increasing complexity or regimes of continuities and contingencies in the Cosmos, the Earth, Life, and Humanity?
Would you expect differences in the ways a historian or a geologist or a chemist might create a history, even if the events in the history were just about the same?
Keep these questions in mind as you dig a bit deeper into the Big History of our world.
Author bio
Bob Bain is associate professor in the School of Education and in the Departments of History and Museum Studies at the University of Michigan. He also is the director of U-M’s World History and Literature Initiative and the faculty lead on the Big History Project. Before coming to the U-M in 1998, he taught high school history and social studies for 26 years. Bain’s research centers on teaching and learning history and the social sciences in the classroom, on-line, in museums, and at home.

Want to join the conversation?