When you walk into the Field Museum in Chicago, Illinois, the first thing you see is a gigantic Tyrannosaurus Rex named Sue. She leans forward in what looks like a hunting posture, her tiny arms extended, her great mouth parted to reveal an arsenal of nine-inch teeth ready to tear you in half with one neat rip and twist. Her gaping eye sockets regard you with solemn intent. This is the ancient greeting of the predator, recognizable even by pampered, modern, city-dwelling humans.

It is lucky for you, therefore, that Sue is dead.

The last time Sue took a living step on land or drew breath from an atmosphere far richer in oxygen than the one we breathe today was over 65 million years ago. Someone found her near Cheyenne, Wyoming, and after a roundabout journey and many back-and-forth arguments and documents attested to and payments exchanged, she arrived at the museum in her well-preserved state.

Sue is one of the most intact T-rex skeletons ever recovered. It is rare that paleontologists are able to extract whole dinosaur skeletons from the ancient bedrock, or nearly whole (a record 90% intact) as in Sue’s case. The prevailing belief is that she died in a swamp or was otherwise somehow covered in water and mud soon after her demise, which prevented other animals from dismembering and carrying away pieces of her ample body.

The first thing you notice about Sue is that she is not as big as you would expect. From numerous over-hyped dinosaur-reincarnation films we have witnessed tyrannosaurs the size of houses, and brachiosaurs and apatosauruses that could crush city buses with a single stomp. But the size of these computer animated monstrosities exceeds reality, as is to be expected from our dear friends in Hollywood.

Sue is somewhat less gargantuan. The impression is that she is more or less the size of your average elephant. Or perhaps a backhoe. From her great torso and massive thighs up to the utilitarian forearms and vast mechanisms of her jaws, her body presents the impression of power equipment. A great piece of natural machinery produced by millennia of evolution to run and bite and kill and eat.

Despite her formidable strength and size, Sue did not have an easy life. Her body shows signs of numerous injuries and pathologies. Her right shoulder blade is damaged, and a tendon in her right arm was torn, perhaps from a struggle with prey. She also had three broken ribs, one which healed in two separate pieces. Her bones show numerous signs of chronic infection. Her spine was arthritic (no great surprise seeing the body it had to support) and there are indications that she suffered from gout.

Sue was 28 years old when she died.

On the surface it is hard to identify with an animal that would have happily crushed you to death with one bite and fed on your innards with relish. But consider her challenges. Torn muscles. Arthritis. Gout. We can recognize these all-too-human conditions and their symptoms because people and animals have them today. Walking talking modern apes like us may not share any direct descendants with the Tyrannosaurus Rex of the late Cretaceous. But we have enough in common to make you wonder where the lineages diverged.

Go back far enough, you will find a common ancestor between us and the T-rex. Hell, dive deep enough into the gene pool and you will find a common ancestor between yourself and mushrooms. That ancestor might be some kind of hideous fish-lizard, or even a jellyfish or frond of algae floating in the gently swaying undersea currents of the primordial ocean. But ancestor it will be.

Life remembers arthritis. Life remembers gout. Life constructs similar mechanisms of bones and tendons and immune systems that break and tear and fail in similar ways, over and over again in an endless repeating cycle, improving and learning and selecting and re-selecting for traits and conditions and environments but repeating just the same. Our cells have been dividing ever since the first cell came up with the notion to split itself in two all those billions of years back into our communal past. In a certain sense, that cell is still alive within us. You might be a new organism walking the earth today, but your DNA remembers a far more ancient past.

All things repeat. All things move in cycles. As events march forward down the corridor of time, familiar places are re-seen and revisited. Recall the famous ascending spiral of the Guggenheim Museum in New York City. As one climbs, you experience the marked wonders of various artists and exhibits as developed over history and time, but always you can look back across the pathway to where you were before, or down to the bottom where you started, or ahead and upward. The destination is obscured, fuzzy, but with a certainty the climb continues.

In the Guggenheim the path ends at the top. You can go no further, but can look up and out and behold a sky and a world and the infinite universe beyond. Even if you do not, the world goes on without you.

Of course, I’m not thinking about any of that when I walk into the Field Museum one frigid day in January. All I’m thinking is, Holy shit, that’s a goddamn T-rex!

I say as much out loud to my then-girlfriend, who smiles and nods and cranes her neck back to look up at the massive skeleton in front of us.

We’re here because we drove down to Chicago from her parents’ house in Minneapolis to check out the city, get a feel for it. It is January 3rd, a few days after the New Year. We have a vague notion that we might end up living here one day. In another few months we will be. Our relationship, however, will not survive the next winter.

Right now though we are still happy, healthy, warm inside the climate-controlled museum with the bitter Chicago weather raking its icy claws against the doors and windows outside. It began to snow last night and there is fresh powder on the lawns and parkways outside, masking the dirty frozen muck that accumulates over the interminable course of the Midwestern winter.

In a city like Chicago all the snow turns gray and brown over the long cold season from grime and pollution and excrement of a million dogs and bums and drunks that wander the streets. Sometimes a rare warm day will melt it all but the next snowfall will lay down a fresh layer, ready to be shat upon anew by the swarming human circus all around. In the lee of buildings where the sun never touches, the stuff gets truly foul.

Last night when the snow started, we were happy because in Minneapolis the winter had been dark and cold but without much snow. When I flew in from California the Midwestern terrain was brown and bleak, bare fields and skeletal trees dotting the wide-open prairie landscape. But then we left for Chicago and, as we sat one night in one of the numerous sports bars drinking pints of dark brown beer and watching the city go by outside, the snow began coming down thick and heavy. Within half an hour the big snowplows were out, piling the stuff up into tall banks on either side of the road and laying down a layer of sharp blue rock salt behind them.

After the snow stopped falling and the plows went home all was still on the street outside. Not many willingly venture out of their warm dens on a night like that in Chicago, so we were almost alone walking back to our hotel, clutching each other, feeling the thickness of our jackets between us, watching our breath mist in the cold night air. There is something special about a fresh snowfall. The air is clear and crisp, biting at exposed skin. Sound all but vanishes and everything gets very quiet. A great white blanket descends over the world, dampening all noise and settling everything into a soft, cold tranquility.

The next day we went down to the Field Museum to walk through the past.

The Field Natural History Museum lies in a large complex of buildings along with the Shedd aquarium and the Hayden planetarium on a tiny peninsula jutting out into the placid waters of Lake Michigan in Chicago, Illinois. As you stand before the tall marble columns marking its entrance, you can look out over the wide, flat expanse of the Great Lake, or back towards the imposing skyline of the city. All cities have a distinctive skyline, and Chicago is no exception. There are the mighty twinned antennae of the Willis Tower, once the Sears Tower. There the massive green diamond of the Crane building. The great obelisk of Hancock Center. From certain vantages the ugly silver phallus of Chicago’s Trump Tower can be seen, however much one might want to ignore it. The view leaves an impression, and is especially impressive from across half a mile of open water.

There was a curious exhibit in the museum that day. Thinking back, I wonder at how lucky we were to arrive there on just that day, at that precise time. The exhibit is still there as far as I know, but if I saw it today, I wouldn’t have seen what I saw in it then. After we left, the idea of the thing stuck with me. I couldn’t shake it. I was affected. Since that day and the order of events which shaped and defined it, I could see my whole life and the lives of everyone in the world who had ever come before and those yet to come falling into place ahead of and behind me. It all suddenly made so much sense.

On the second floor of the museum, there was a special exhibit. In this exhibit, a number of halls had been converted to a series of displays, complete with models, infographics, specimens and a guided path that took you from one part of the exhibit to the next. It was called “Evolving Planet” and featured a whole chronology of life on Earth from its inception to the present day. At first there appeared to be nothing unique about this particular set of displays. After all, most historical museums feature a timeline of some kind.

What made this exhibit unique was that it was separated into periods of time between mass extinction events. The one that killed the dinosaurs just one among a myriad of others. There are six widely recognized major extinction events (and many more minor ones) in Earth’s history, marked by the boundaries between time periods in which they occurred: the Ordovician-Silurian, the late Devonian, the Permian-Triassic, Triassic-Jurassic, and Cretaceous-Paleogene.

The exhibit culminated with the sixth and final event, the Holocene extinction.

The Holocene is the time period in which we modern humans live.

The latest extinction event is happening right now.

In the museum, the exhibit is well-planned. They don’t hit you with the big reveal until the end. With all the flair and sleight-of-hand of the best magicians, the designers lead you down the garden path, saving the best for last.

When you enter, the first hall is a parade of deep-sea trilobites and barren land masses devoid of plant life. In the history of the world, this is the time beyond when the seething molten mass that was the primordial Earth has settled into a semblance of solidity and the oceans have had time to expand and fill with water. The exact mechanism by which so much liquid water was deposited on the planet is still unclear, much like the precise origins of life itself. But at any rate, we had oceans. Life was thriving and expanding within them. Species were experimenting with different shapes and sizes and occupations. Life fed on life and grew and changed and molded itself to greatest success within its environment.

Then something happened.

The most widely accepted hypothesis is that two periods of massive and rapid climate change at the end of the Ordovician and beginning of the Silurian periods were just too much for most species to handle. The Earth cooled rapidly and glaciers began to form, drawing water out of the oceans and lowering sea levels so that creatures who lived along the continental shelves were exposed to air or shallower water and to higher levels of ultraviolet radiation than animals who lived deeper in the ocean. The atmosphere also changed due to widespread volcanic eruptions, and levels of carbon dioxide actually dropped immensely, which had a detrimental effect on many organisms.

The extinction was global. 85% of marine species vanished forever.

In the Field Museum, the exhibit marks the transition between one period of life on Earth and the next which follows the mass extinction with a great square archway. The space within is pitch black and lit with a band of threatening red light. MASS EXTINCTION, reads a sign. 85% OF ALL LIFE GOES EXTINCT.

Beyond the archway the next stage of natural history can be seen. Trilobites and jawed fish swim in renewed ocean waters and on land a forest of ferniferous plants and trees reaches skyward. Giant insects soar and buzz in the oxygen-rich air of an adolescent Earth, which has survived its first set of growing pains and now sprinting with excitement towards maturity.

Millions of years of history are here reduced to single footsteps. Take one step and you cover ten million years. Whole geological ages are consumed with a short stroll from one display to the next.

It is so easy to see the world as fixed and immutable. Looking around you can see the world as it is now and believe that it has always been this way and always will be. But our lives are so short when measured against the history of the planet we live on. We use terms like millions or billions of years without truly grasping the significance of such a span of time. The entirety of human civilization has taken place more or less within the last ten thousand years, a fraction of even a single million-year epoch. We have no recorded history beyond that and so to us there is nothing but a great darkness coming up behind and swallowing all possibility of memory.

But the Earth remembers. The stones beneath our feet hold the imprints of that vast black ocean of time swimming behind us. In places where great continental uplift or strong weathering has occurred (think the cliffs of Dover or the Grand Canyon of Arizona) we can see the record that time has left us. The darkness of prehistory is not so dark thanks to what we are able to see and divine from such natural afterimages left without design or intention for us to see. We are the first living creatures with the capacity to understand the true complexity and all the interacting forces and events which have led to this place and time in the world and the Universe.

But time is relative. Our modern human lives take place within a speedy hundred years or so. But a hundred years is a moment of an eyeblink of a fraction of a tail-shake in the natural history of the world, and as such we understandably cannot perceive events which take place over thousands or millions or billions of years. Even changes over decades within our own short lifespans are difficult to detect without careful reflection.

And so, we must use our imagination to see these things. The incredible brains we possess give us the ability to understand such things in representation. We can write down the order of events as we understand them that led from the beginning of the world to this day. We can draw timelines marking the separations in epochs, images of the creatures we see drawn from the fossil record, sculptures and recreations in paint and plaster of the world which came before. We can build museum exhibits that tell us where we are and how we got here. Re-creations and dioramas which show us the cataclysms which have marked great divisions in the history of life on Earth. We can see what has happened before countless times.

Things which will necessarily happen again.

The fact that we are living through one of the top six greatest mass extinctions ever to occur in the history of the world right now, at this very moment, is lost on most people. For one thing it is just not widely known. For another, how are we to recognize something that takes place over hundreds, even thousands of years, with our limited perspective on time?

It started with Neanderthals and the first Homo sapiens and other proto-humans. The control of fire and the birth of technology and development of weapons gave us the power to control and shape the natural world around us. And the first thing we did was start to kill everything else in sight. There are dozens of ice-age species, for example, that were hunted to extinction by humans. For example, it is thought by some that the wooly mammoth might still exist today in some form if it weren’t for us, since it was so heavily hunted.

All talk of climate change aside, obvious as its effects might be, what is more obvious and less controversial is that we are squeezing out most other forms of life. The sheer number of humans and the demand that we put on our environment takes a heavy toll on the natural world. Wherever humans increase, everything else decreases. Statistics are unnecessary. The silence in what remains of the fields and forests and at the edges of our cities says all that is needed to be said.

It is so hard for us to envision these things on the needed scale to truly behold them. But with our imagination and our technology we can help ourselves to see what is happening to us right now, beyond the diminished perspective that our brief lives provide, winking in and out of existence like the spark of a firefly on a warm summer night.

We can build portals to the past and tunnel doorways into time.

Take a step through one of these doorways, and you travel through ten million years from the distant past into what then was still the future. From a time of great abundance to a time of unbelievable change and death on an unimaginable scale.

Take a step from light into darkness. Total blackness, silent and complete. Red light engulfs you and enlightens you. 85% of all life. Thousands of species. Millions, perhaps billions of individuals.

Gone in the space of a single footstep.

Before you is the future. Another step and you will enter a whole new world where life has taken on new shapes and forms but always following the same basic pattern. The cell divides. What you see before you is a copy of a copy of a copy of a copy, darkened and brightened and smudged and torn and reassembled and reimagined. Life which has exploded in diversity but which, if you go back far enough, all shares the same beginning. Plants and animals and fish and insects all born from a molecule that became a cell that became two cells that became four. And so on. And so on. And so on.

Step, and the cell divides.

Step, and death becomes you.

Step, life is reborn and renewed.

One foot in front of the other, from now until forever.