The Scale of Time: From Heartbeats to the Heat Death of the Universe

Summary

This exploration of time scales reveals the extraordinary context of human existence within the vast temporal landscape of Earth and the universe. The article demonstrates how the human perception of time represents an infinitesimally small fraction of cosmic history. Our 70-year average lifespan constitutes less than 0.000002% of Earth's 4.6-billion-year history.

Our journey through time begins with human scales. All of recorded history spans merely 400 generations. This represents only 2% of the 300,000-year existence of our species. The article uncovers Earth's dynamic 4.6-billion-year biography written in layers of rock, continental drift and mass extinctions. It explores the 165 million year age of dinosaurs and the 66 million years which have elapsed since their extinction. It reflects on astronomical time scales which stretch our comprehension even further. A cosmological perspective is necessary to encompass the universe's 13.8-billion-year history and project into a distant future where star formation ceases and black holes evaporate.

Key Takeaways

Human existence is extraordinarily brief in geologic terms: A human lifetime represents less than 0.000002% of Earth's history and only 400 generations have lived across recorded history.

Dinosaurs dominated Earth far longer than humans have existed: Dinosaurs ruled for 165 million years (550 times longer than humans). The Cretaceous period lasted longer than the subesequent 66 million years.

Earth's history reveals constant change and mass extinctions: Our planet has experienced at least five major mass extinctions that reset evolutionary development.

The universe operates on vastly different timescales: Our galaxy takes 225-250 million years to complete one rotation. Massive stars burn out in 10-50 million years and red dwarfs can shine for 10 trillion years.

The far future stretches beyond human comprehension: Star formation will cease in 100 billion years and the last stars will die in 12 trillion years.

Understanding time's scale transforms our perspective on existence: This cosmic viewpoint inspires both humility about our brief moment and wonder at being part of a 13.8-billion-year story of the universe.

A Fundamental Dimension of Existence

Time is perhaps the most fundamental dimension of our existence. Yet its true scale remains one of the most difficult concepts for humans to grasp. We live our lives in seconds, minutes, and years. The universe operates on timescales stretching from the infinitesimally brief to the unimaginably vast. Understanding these different scales of time helps us appreciate our place in the cosmos. They reveal the extraordinary story of how everything we know came to be.

How Long is a Human Lifetime in the Context of Time?

The average global human lifetime is just over 70 years. But what does this truly represent? A human life occupies less than 0.000002% of Earth's 4.6-billion-year history. It represents an even smaller fraction of the universe's 13.8-billion-year timeline.

Our understanding of time is enmeshed fundamentally in the human experience. A human heartbeat lasts roughly one second. A conversation might span minutes. Our daily routines cycle every twenty-four hours. But familiar numbers can quickly become strange and alien when viewed from a different perspective. An eighty year lifespan translates to approximately 700,000 hours of conscious experience. One might say we live for an average of 42 million minutes.

Consider the following: Anatomically modern humans have existed for 300,000 years and organized human societies emerged approximately 10,000 years ago. A human generation is widely understood to be around 25 years. This means there have been a mere 400 generations of humans in all of recorded history. The totality of human achievement represents only 2% of the existence of our species.

The Industrial Revolution began around 1760. The subsequent two hundred and sixty-five years represents a mere four human lifetimes. Modernity has been transformed by the internet. A world without constant and omnipresent connectivity would be unimaginable to many. Yet the modern version of what has become the most fundamental technology powering our lives is only thirty-two years old. These timescales constitute mere moments when viewed across the fullness of time.

Human history reveals surprising temporal relationships that challenge our intuitive understanding of the past. We are closer in time to Cleopatra VII (who died in 30 BCE) than she was to the construction of the Great Pyramid of Giza. About 2,000 years separate us from the last pharaoh of Egypt. Approximately 2,500 years separated Cleopatra from the pyramid's construction in 2580 BCE. The Great Pyramid was already ancient in Cleopatra’s time. She looked upon this wonder of the ancient world in the same manner as we view the Colosseum today. Modern audiences will perhaps appreciate other interesting quirks of time: We are further away from the release of the PlayStation in 1994 than the PlayStation was to the Japanese release of the NES in 1983. Marty McFly would have traveled back to 1995 if Back to the Future was set in 2025.

Historical Time Comparisons

• Human species existence: 300,000 years
• Human recorded history: 5,000 years
• Agriculture development: 10,000 years ago
• Industrial Revolution: 265 years ago
• Internet age: 32 years

Our timer, stopwatch and alarm will satisfy all your timekeeping needs on a human timescale. More sophisticated tooling will regretfully be necessary when measuring time across longer spans, however.

What Can the Geologic Time Scale Show Us?

Geologic time is not measured in decades or centuries. It is measured in millions and billions of years. The system used by geologists to describe the timing and relationships of events in Earth's history is known as the geologic time scale. Geological time reveals a biography written in layers of rock, fossils and continental shifts.

Earth formed approximately 4.6 billion years ago. The planet has undergone dramatic transformations throughout its history. Oceans formed, continents drifted and life emerged. Major geological events demonstrate the planet's dynamic nature over these vast timescales. The breakup of the supercontinent Pangaea began 175 million years ago. The continents continue to drift at rates of centimeters per year. Mountain ranges like the Himalayas formed over tens of millions of years through the collision of tectonic plates. The Grand Canyon was carved by the Colorado River over a period of approximately six million years.

Cycles of Destruction and Renewal

Geological time also reveals the fragility and resilience of life. Mass extinctions which each eliminated 75% or more of all species reset the evolutionary clock on at least five occasions. The most famous mass extinction event occurred 66 million years ago and ended the age of the dinosaurs (known as the Mesozoic Era). Their extinction was likely caused by an asteroid impact near the Yucatán Peninsula which coincided with the disappearance of dinosaurs from the fossil record.

The age of the dinosaurs provides a useful illustration of the vastness of geologic time. The Mesozoic lasted from about 252 to 66 million years ago. It is divided into three distinct periods: the Triassic (252-201 million years ago), Jurassic (201-145 million years ago) and Cretaceous (145-66 million years ago). Each period was longer than the entire span from the extinction of dinosaurs to today. The Jurassic Period alone lasted 56 million years. That is nearly 300,000 times longer than all of recorded human history.

Did People and Dinosaurs Live at the Same Time?

The gap between the end of the Cretaceous period (when dinosaurs went extinct) and the emergence of early human ancestors like Australopithecus is about 62 million years. More time separates us from T. rex than separated T. rex from Stegosaurus in the Jurassic Period about 150 million years ago. The iconic dinosaurs we imagine living together actually existed tens of millions of years apart.

Mesozoic Era Quick Facts

• Triassic period: 252-201 million years ago (51 million years duration)
• Jurassic period: 201-145 million years ago (56 million years duration)
• Cretaceous period: 145-66 million years ago (79 million years duration)
• T. rex to humans: 66 million years
• Stegosaurus to T. rex: 84 million years
• The Cretaceous period was longer than the 66 million years that followed

A simple way to understand the breadth of geological time is to think about the history of the world if it occurs over a single year. What would this look like? Earth would form on January 1st. First life would not appear until late February. Complex cells with nuclei only emerge in August. The first animals appear in November. Dinosaurs don’t arrive until December 20th. Humans appear in the final hour of December 31st. All of recorded history occurs in the final seconds before midnight.

Understanding Earth's History in One Year

• January 1st: Earth forms
• Late February: First life appears
• August: Complex cells develop
• November: First animals emerge
• December 10th: Dinosaurs arrive
• Final hour of December 31st: Humans appear
• Last few seconds: All recorded human history

The scale of planetary time is truly vast. But what happens when we zoom out further into the murky temporal depths beyond the boundaries of our world? We find ourselves in a dialog with the stars and the eternal recesses of the universe itself.

What is the Time Scale of the Universe?

The universe began approximately 13.8 billion years ago with the Big Bang. It is three times older than Earth. The cosmic timeline encompasses the formation of the first stars, the synthesis of heavy elements and the emergence of planets capable of supporting life over billions of years. Astronomical time dwarfs geological timescales. It stretches our comprehension of time to its limits.

The life cycles of stars operate on timescales spanning millions to trillions of years. Massive stars burn through their nuclear fuel relatively quickly. This reduces their lifespan to only 10-50 million years before exploding as supernovae. Our Sun is a medium-sized star. It has already lived for an estimated 4.6 billion years. It will continue shining for another 5 billion years before expanding into a red giant and eventually becoming a white dwarf.

The smallest stars are known as red dwarfs. They are the universe's ultimate survivors. Red dwarfs are dim and cool. They burn their nuclear fuel so slowly they can shine for trillions of years. Some red dwarfs born today will still be shining when the universe is a hundred times older than it is today.

Stellar lifetimes

Galactic timescales add another dimension to cosmic time. The Milky Way galaxy rotates once every 225-250 million years. This period is referred to by astronomers as a galactic year. The sun has completed only about 20 orbits around the galaxy since it formed. The nearest major galaxy is known as Andromeda. It is approaching us at 110 kilometers per second and will collide with the Milky Way in approximately 4.5 billion years. The Andromeda-Milky Way collision will create a new galaxy some astronomers have dubbed Milkomeda.

What will happen in 100 billion years?

Astronomical timescales become almost incomprehensibly vast when looking into the distant future. Current cosmological models suggest the universe will continue expanding and cooling for trillions of years. Star formation will cease in about 100 billion years. The last red dwarf stars will die in 12 trillion years. Black holes will evaporate through Hawking radiation over timescales of 10¹⁰⁰ years.

Until the Light Takes Us

Star formation will gradually cease as the universe runs out of the hydrogen needed to create new stars. The expansion will carry distant galaxies so far away their light will no longer reach us. The universe will plunge into darkness. Future observers will be left in a universe appearing to contain only their local galaxy group. Stellar remnants like white dwarfs and neutron stars will dominate the cosmos 10¹⁴ (one quadrillion) years from now.

Even these remnants won't last forever. Proton decay will cause all matter to disintegrate over timescales of 10³⁴ (one hundred decillion) years if it occurs as some theories predict. Black holes are the most persistent objects in the universe. Yet even these will eventually evaporate through Hawking radiation. The largest black holes will take 10¹⁰⁰ years to disappear completely.

The ultimate fate of the universe depends on the nature of dark energy. It is this energy which drives cosmic expansion. The universe could experience a Big Rip in about 22 billion years as a result of the gravitational effects of dark energy. The Big Rip would tear apart all matter as the distances between particles infinitely increase. A competing hypothesis is that the universe might recollapse in a *Big Crunch. This will potentially give birth to a new universe but would not happen for trillions of years.

A timeline of the far future

• 22 billion years: Potential Big Rip scenario
• 100 billion years: Distant galaxies disappear beyond the observable horizon
• 1 trillion years: Last red dwarf stars begin to die
• 10¹⁴ years: Stellar remnants dominate the universe
• 10³⁴ years: Proton decay destroys all matter (theoretical)
• 10¹⁰⁰ years: Last black holes evaporate

Why Does Understanding the Scale of Time Matter?

Grasping the scale of time transforms our perspective on existence itself. It reveals the stable and permanent-seeming world around us to be part of an ongoing story of constant change and evolution. Mountains rise and fall. Continents drift. Species emerge and vanish. Stars are born and die as in cosmic processes operating on timescales far beyond human experience.

Understanding time's scale inspires both humility and wonder. It reminds us we are part of an ancient and ongoing cosmic story. We are sojourners in a 13.8-billion-year stellar odyssey of increasing complexity and beauty. Our brief moment in time is made more meaningful by understanding the vast temporal landscape in which it unfolds.

Frequently Asked Questions About Time Scales

How long did dinosaurs exist compared to humans?

Dinosaurs dominated Earth for approximately 165 million years (from 230 to 65 million years ago), while modern humans have existed for only 300,000 years. Dinosaurs ruled Earth for 550 times longer than humans have existed.

When did humans first appear on Earth?

Anatomically modern humans (Homo sapiens) first appeared approximately 300,000 years ago in Africa. However, human ancestors began diverging from other primates around 7 million years ago.

What came first: the pyramids or Cleopatra?

The Great Pyramid of Giza was built around 2580 BCE, while Cleopatra VII died in 30 BCE. The pyramids were built about 2,550 years before Cleopatra's time, making them ancient even to her.

How old is Earth compared to the universe?

Earth is 4.6 billion years old, while the universe is 13.8 billion years old. This means Earth formed about 9 billion years after the Big Bang, when the universe was already two-thirds of its current age.