The Mihir Chronicles

A Brief History Of Earth by Andrew H. Knoll

September 10, 2021

I. Brief Summary

This was gifted to me by my wife on my birthday. It was a great tour of everything about our planet Earth. This book is written by an influential geologist and a professor who has dedicated his entire life studying the history of our planet. Understanding the geologic history is critical to understanding where our planet is headed. The book is filled with lessons on transformations—life, sea, atmosphere, mass extinctions, animals and humans. Andrew Knoll pleas on climate crisis led by humans in the beginning and at the end. I learned quite a bit about the transformation of the Earth, but also the importance of really how long it takes for evolution to take place and ruining it in a few decades have dire consequences to sustain our lives.

II. Big Ideas

  • Rocks offer a grand narrative of Earth's development from youth to maturity.

  • Earth's Greatest Oxygenation Event

    • One thing is clear: oxygen was not part of early atmosphere.
    • Four billion years ago, the Sun's luminosity was only about 70 percent of its modern value. If the Sun was dim, why wasn't the early Earth an ice ball? The answer is “greenhouse gases,” the bane of twenty-first century global warming but the long-term guarantor of habitable climate.
    • The question of life without oxygen is relatively easy to address because oxygen-free environments exist today.
    • Both photosynthesis (plants) and respiration (animals) are complementary to each other. As a consequence, carbon and oxygen cycle back and forth between organisms and the environment, sustaining life through time. But once upon a time the imbalances between the two gases could not have sustained human life. If we were to time travel back, we would be asked to bring-our-own-oxygen to the party.
    • Early Earth was swaddled by a thick atmosphere, but it was air without oxygen. Sun's luminosity was only about 70 percent of its own modern value. Sun was dim, but our planet was liquid, not an ice-ball. Why? Greenhouse gases. Carbon dioxide (CO2) must have been present at more than 100 times its current concentration. Given Earth has been biological most of its life, early life therefore survived on greenhouse gas such as carbon dioxide.
    • Earth's Greatest Oxygenation Event was revolutionary, and Cyanobacteria—the only bacteria capable of oxygenic photosynthesis—were the heroes of the revolution. Cyanobacteria gained the upper hand in a world that long favored different photosynthetic microbes. They dominated the planet by producing more oxygen than carbon.
  • Human Earth

    • Hominins differed from other great apes in critical way. They walk upright.
    • Early humans lived only in Africa, but a bit more than 100,000 years ago, one population stuck its toe into the wider world, dwelling in what is now Israel along with Neanderthals. Then, 50,000-70,000 years ago, our species spread rapidly throughout Asia and Europe.
    • Homo sapiens has shaped the world around us since our inception and now does so in unprecedented ways, the latest movement in the long symphonic dance of Earth and life.
    • The human population, whom we call Clovis—suggests that humans played a major role in removing large mammal species from North America.
    • Agriculture and pollution are both challenging natural ecosystems. For example, there are dead zones, meaning depleting oxygen in ambient waters found in Gulf of Mexico and other coastal seaways.
    • Globally, hunting has depleted numerous bird and mammal populations.
    • One in six global fisheries has collapsed in recent decaded. Commercial fishing was banned, but nearly three decades later, the cod have yet to recover.
    • It is estimated that about one garbage truck worth of plastic enters the oceans every minute.
    • Charles David Keeling began to monitor the composition of the atmosphere, taking hourly readings from a station atop Mauna Loa, a program that continues today. When Keeling started, the air above Hawaii contained 316 parts per million carbon dioxide. By May 2020, CO2 had increased to 417 ppm, a value last seen of Earth millions of years ago.
    • CO2 increase is driven mainly by the burning of fossil fuels because of chemical signature to their air. Carbon-14 in atmospheric CO2 has declined through time so the principle source of atmospheric CO2 is identified to coal, petroleum and natural gas burned by humans.
    • National parks, refuges, and other protected lands play a critical role in the conversation of species threatened by habitat disruption. Species that didn't encounter each other in the past will occur with largely unknown consequences for competition and ecosystem resilience.
    • As CO2 increases, oceans and land surface will become warmer. As water warms, it will carry less oxygen gas and ocean will absorb more carbon dioxide. This will in turn lead to decline in pH of seawater. This has disturbed reef corals. This chain reaction have many unknown consequences.
    • Humans have been pumping greenhouse gases into the atmosphere increasing the magnitude and frequency of heat waves, drought, and storms. With this in mind, what has been depressing is the human response. Each year we do nothing makes the task of solving the climate crises grow larger.

III. Quotes

  • Our attachment to the Earth extends well beyond gravity.
  • With every breath you bring oxygen-rich air into your lungs, enabling you to gain energy from your dinner.
  • The steel in your refrigerator door, the aluminum in your “tin” cans, the copper in your pennies, and the rare-earth metals in your smartphone all come from within the Earth.
  • Small changes add up through time.
  • The story of Earth and the organism it sustains is far grander than any Hollywood blockbuster, filled with enough plot twists to rival a bestselling thriller.
  • Somehow om this dynamic stage, life established a foothold and eventually transformed our planet's surface, paving the way for trilobites, dinosaurs, and a species that can speak, reflect, fashion tools, and in the end, change the world again.
  • Population decline is not extinction, but it is road down which species travel on their way to biological endgame.
  • In the end, we will conserve only what we love, we will love only what we understand, and we will understand only what we are taught. — Baba Dioum
  • Our understanding of the universe and its history comes largely from the most ephemeral sources: light. That's what makes our starry sky a celestial history book.
  • If light chronicles the history of the universe, rock tell our planet's history.
  • Earth writes its history with one hand and erases it with the other.
  • The full moon may inspire poetry, but it was born in violence.
  • If geologists have a mecca, it is Siccar Point.
  • We might volunteer that organisms grow. True, but so do quartz crystals. But organisms not only grow, they reproduce.
  • Life, then, is characterized by growth and reproduction, metabolism, and evolution.
  • Even the simplest bacteria are complicated molecular machines.
  • DNA, the cell's instruction manual and evolutionary memory.
  • Earth has been a biological planet for most of its long history.
  • This was the anvil of which life was forged, and had you been there (don't forget to bring your own supply of oxygen) you might not have noticed the changes underfoot.
  • How did Earth get into this deep freeze and, as important, how did it get otu again?
  • By the time the glacier collapsed, some 70 percent of all known animal species had disappeared.
  • 400 million years ago, land plants already lived in close association with fungi, exchanging food for nutrients. In the absence of this partnership, Earth's green revolution might have never occurred.
  • Vertebrates, our own ancestors, were relatively late comers to the party.
  • The principal physical part of soil formation—chemical weathering—is itself enhanced by roots that penetrate into the subsurface, releasing organic acids as they go.
  • Mass extinctions have clearly played a role in shaping evolutionary history.