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The story of Earth is an epic filled with crises, catastrophes, and remarkable, repeated change. Earth traces its origin to simple atoms that were created in the big bang, transformed into heavy elements in stellar explosions, and then forged into a planet inside the nebula that gave birth to the solar system. Like many other planets, Earth went through phases of melting, volcanism, and bombardment by asteroids. But only on Earth did events lead to a flourishing biosphere—life. And once life was established, it drove the evolution of our planet in startling new directions.
episodes:
01. Mineralogy and a New View of Earth
Begin your study of Earth’s history by voyaging backward in time, seeing how each crucial stage in the evolution of our planet depended on what came before. Preview the surprising role played by minerals, which coevolved with life—a link that provides a revolutionary new way of understanding Earth.
02. Origin and Evolution of the Early Universe
Earth has existed for only a third of the history of the universe. What happened before our planet formed? Journey back to the big bang, learning how fundamental forces and particles froze out of a homogeneous state in the initial moments of cosmic evolution.
03. Origins of the Elements—Nucleosynthesis
Discover how simple atoms of hydrogen and helium make stars, and how stars manufacture all other naturally occurring elements through processes including titanic supernova explosions. Called nucleosynthesis, this remarkable mechanism is responsible for the chemical richness that made Earth possible.
04. Ur-Minerals, First Crystals in the Cosmos
Trace the origin of minerals and discover a surprising candidate for the first crystal forged in the cauldron of dying stars. Then follow the processes that created other early minerals, which survive in their original form in microscopic presolar dust grains in interplanetary space.
05. Presolar Dust Grains—Chemistry Begins
Unravel the story told in “presolar” grains of dust formed by stars very different from our sun. These are the earliest building blocks of our own solar system. Learn how scientists identify these microscopic particles, which often contain diamond crystals. Also see how the field of cosmochemistry is revolutionizing the study of minerals.
06. Coming to Grips with Deep Time
Plunge into deep time—the vast period that reaches back to Earth’s beginning. Professor Hazen walks you through a memorable analogy that orients you along this sea of ceaseless change. Also explore the techniques that allow scientists to date rocks and other materials with astonishing precision.
07. The Birth of the Solar System
Where did Earth and the solar system come from? See how an idea proposed in the 18th century provides a simple and elegant answer to this question. Compare our solar system with other planetary systems that have recently come to light in the successful search for extrasolar planets.
08. The Early Solar System—Terrestrial Planets
Investigate the work of the most successful planet-hunter of all time: the Kepler spacecraft, which found thousands of candidate planets orbiting other stars. Then focus on the origin of the four terrestrial planets in our inner solar system: Mercury, Venus, Earth, and Mars.
09. Hints from the Gas Giants and Their Moons
Tour Jupiter, Saturn, Uranus, and Neptune—the four gas giants of the outer solar system. Each is a mammoth world of violent weather, and each has multiple moons that help shed light on Earth’s story. View this strange realm through the eyes of far-traveling space probes.
10. Meteorites—The Oldest Objects You Can Hold
Most meteorites that fall to Earth are older than Earth itself. Review our understanding of these artifacts of the solar nebula, learn where most meteorites are found, and hear about Professor Hazen’s experiences searching for meteorites in the murky world of international meteorite trading.
11. Mineral Evolution, Go! Chondrite Meteorites
Focus on the most numerous class of meteorites: chondrites. These incredibly ancient rocks tell a story of intense pulses of radiation from the infant sun, which melted dust grains into sticky rocky droplets called chondrules. Countless chondrules clumped together to form chondrite meteorites.
12. Meteorite Types and Planetesimals
As planetesimals grew, the primary chondrite minerals were altered in ways that formed a different class of meteorites: achondrites. Study these fascinating relics from destroyed mini-planets. Some achondrites were blasted off the moon and Mars, including one specimen purported to show evidence of ancient extraterrestrial microbes.
13. Achondrites and Geochemical Affinities
Having surveyed the first stage of mineral evolution during the solar nebula phase, turn to stage two, which saw an explosion of mineral diversity during the accretion of protoplanets. One key to understanding how minerals began to diversify during this period is the influential classification scheme developed by geochemist Victor Goldschmidt.
14. The Accretion and Differentiation of Earth
Follow the stages of Earth’s initial formation, as solar system debris in our neighborhood of space collided until one object dominated, growing into the embryonic Earth. Trace the process of differentiation that produced a distinct core, mantle, and crust; and learn how scientists know the details of Earth’s deep interior.
15. How Did the Moon Form?
Investigate the case of the massive moon. Where did Earth’s unusual moon come from? Explore the three possibilities considered before the Apollo moon landings gave scientists actual lunar samples to analyze. Also hear the story of Professor Hazen’s close encounter with moon dust.
16. The Big Thwack!
Continue your investigation of the moon’s origin. The simplest theory that explains the evidence is the “big thwack” model. Study this scenario, which has all the drama of a disaster movie—with colliding planets and a giant moon filling Earth’s sky and then slowly receding over the course of billions of years.
17. The “Big Six” Elements of Early Earth
Survey Earth’s six dominant elements: oxygen, magnesium, aluminum, silicon, calcium, and iron. Each has played a key role in Earth’s history, governed by the element’s distinctive chemical character. Examine this chemistry and learn, for example, why virtually all oxygen on the planet is locked in minerals and rocks.
18. The Black Earth—Peridotite to Basalt
Trace the evolution of Earth’s first rocks, which crystallized from the young planet’s seething magma oceans. Peridotite was the earliest major rock type to form. Discover why peridotite is now found mostly deep in the mantle, while a related rock called basalt covers 70 percent of Earth’s surface.
19. Origins of the Oceans
Follow Earth’s remarkable transition from a dry world with a uniform black basaltic surface to a wet planet of rivers, lakes, and oceans. Also learn about the special properties of water, which make it a universal solvent, a vehicle for life, and the chief architect of Earth’s surface features.
20. Blue Earth and the Water Cycle
Hunt for unseen water on the moon, Mars, and Earth, discovering that copious quantities exist in unlikely places, including hundreds of miles underground. Professor Hazen tells how his lab duplicates conditions in Earth’s deep interior to learn how minerals incorporate water under extreme pressure.
21. Earth and Mars versus Mercury and the Moon
Search for the reason that Earth and Mars have far greater mineral diversity than Mercury and Earth’s moon. Probe clues such as tiny zircon crystals that are the oldest surviving minerals on Earth. From this evidence, assemble a story of Earth’s global ocean and a time when the entire planet froze over.
22. Gray Earth—Clays and the Rise of Granite
Probe the essential features of clay minerals, which are abundant on both Earth and Mars. Then investigate why Earth has so much granite. Trace the origin of this rock, which abounds in Earth’s continents but is rare elsewhere in the solar system.
23. Earth’s Mineralogy Takes Off—Pegmatites
Continue your study of the stages of mineral evolution by looking at what happens when granite partially melts. Under the right conditions, the resulting crystals can be unusually large and strikingly beautiful. Such rocks are called pegmatites, and their formation involves some of the rarest elements on the planet.
24. Moving Continents and the Rock Cycle
Explore early attempts to explain why the continents fit together like pieces of a jigsaw puzzle, including Alfred Wegener’s continental drift theory and the expanding Earth hypothesis. Lay the groundwork for an understanding of the revolutionary theory of plate tectonics by reviewing the stages of the rock cycle.
25. Plate Tectonics Changes Everything
Research after World War II converged on a remarkable theory for the evolution of Earth’s crust and upper mantle: plate tectonics. Study the evidence that led scientists to conclude that a dozen shifting plates explain earthquakes, volcanoes, mountain ranges, deep sea trenches, and much more.
26. Geochemistry to Biochemistry—Raw Materials
Investigate the problem of defining life, focusing on the organic raw materials from which life must have begun. Learn that these materials are surprisingly common across the universe. Finally, look at the recent discovery of extremophiles and the implications for the existence of life on other worlds.
27. Biomolecules—Select, Concentrate, Assemble
Focus on the role of minerals in the origin of life. Nothing matches the solid, crystalline surfaces of minerals in their ability to select, concentrate, and assemble the biomolecules that are instrumental for life. Professor Hazen describes his lab’s groundbreaking research in this field.
28. Why Reproduction? World Enough and Time
What was the first collection of molecules that could copy itself? Investigate three theories of early reproduction: the reverse citric acid cycle, autocatalytic networks, and self-replicating RNA. Then travel to the world 3.8 billion years ago to consider conditions on Earth when life got its first foothold.
29. Eons, Eras, and Strategies of Early Life
By 3.5 billion years ago, life was established on Earth. After reviewing the geological timescale, follow the development of life over its first billion years, learning that biochemical processes mimicked the existing chemistry of rocks and gradually altered Earth’s surface environment.
30. Red Earth—The Great Oxidation Event
By 2.4 billion years ago, Earth’s atmosphere contained a small but significant amount of molecular oxygen. Where did it come from? Explore this dramatic development, in which cells evolved to gain energy from the sun while producing oxygen as a waste product.
31. Earliest Microbial and Molecular Fossils?
See how three rare and distinctive ancient rock types—black carbon-rich chert, black carbon-rich shale, and mound-like stromatolites—provide tantalizing evidence for life on Earth more than 3 billion years ago. Focus on the researchers who have blazed the trail in this challenging field.
32. Microbial Mats and Which Minerals Can Form
Carpet-like colonies of algae called microbial mats date back almost to the dawn of life. Because they use photosynthesis, microbial mats help date the Great Oxidation Event. Trace the far-reaching consequences of an oxygen-rich atmosphere on the evolution of minerals.
33. Earth's Greatest Mineral Explosion
Investigate the rise of mineral diversity in the wake of the Great Oxidation Event—a diversity that has far surpassed anything on other planets in the solar system. Discover that new minerals appeared, not steadily, but during relatively short episodes of intense activity associated with the formation of supercontinents.
34. The Boring Billion? Cratons and Continents
After the dramatic changes of Earth’s first 2.5 billion years, what came next appears to be a “boring billion” years of stasis. Turn back the clock to see what was really happening during this period, when continents were assembling around rugged pieces of proto-continental crust called cratons.
35. The Supercontinent Cycle
From a plate tectonics point of view, the boring billion was action-packed. Follow the formation and break-up of supercontinents, probe the nature of the global superocean, and identify the reasons that life on Earth changed little during this interval of radically altering geography.
36. Feedback Loops and Tipping Points
If pushed too far, Earth’s systems can become unbalanced and reach tipping points, with consequences for climate and life that are difficult to predict. Study the lessons of 850 million years ago, when the breakup of the Rodinia supercontinent caused a cascade of dramatic changes.
37. Snowball Earth and Hothouse Earth
Some 750 million years ago, Earth entered a period of extreme climate instability, starting with a brutal ice age. Seek the explanation for almost 200 million years of back-and-forth swings between snowball and hothouse phases. Also probe the evidence that Earth completely froze over.
38. The Second Great Oxidation Event
In a perfect demonstration of the interaction between geology and life, see how the snowball-hothouse cycles led to a Second Great Oxidation Event, which raised the level of oxygen to near-modern levels for the first time. Discover how different scientist teams deciphered the clues.
39. Deep Carbon—Deep Life, Fuels, and Methane
Cover the Deep Carbon Observatory, Professor Hazen’s 10-year, billion-dollar research project to understand the cycling of all forms of carbon on Earth, from the surface to deep in the planet. Focus on the mystery of the origin of Earth’s methane.
40. Biominerals and Early Animals
Having journeyed through almost 90 percent of Earth’s history, finally arrive at the evolution of animals. Learn how the animal kingdom would not have been possible without minerals. Professor Hazen shares his lifelong fascination with one ubiquitous early animal: trilobites.
41. Between Rodinia and Pangaea—Plants on Land
Once ozone collected in the upper atmosphere, life no longer had to stay submerged to avoid the sun’s damaging ultraviolet radiation. Survey the first half of the Paleozoic Era, between 542 and 400 million years ago, when a great green revolution occurred on dry land.
42. Life Speeds Up—Oxygen and Climate Swings
Focus on the second half of the Paleozoic, between 400 and 250 million years ago, when oxygen reached its highest levels ever. Terrestrial vertebrates emerged and life went through many crisis points, with repeated episodes of extinction followed by intervals of evolutionary novelty.
43. From the “Great Dying" to Dinosaurs
Search for the cause of the worst catastrophe ever to befall Earth’s biosphere: the Permo-Triassic Extinction, also called the Great Dying, which occurred roughly 250 million years ago. Then follow the rise of the dinosaurs, which became the dominant vertebrates for the next 185 million years.
44. Impact! From Dinosaurs to Mammals
The most famous of all extinctions occurred at the end of the Cretaceous period, 65 million years ago. Analyze the role of an asteroid in this turning point in the evolution of mammals and other groups, which managed to survive and flourish while dinosaurs and countless other species perished.
45. Humans and the Anthropocene Epoch
Study the place of humans in geological time, the most recent portion of which has been called the Anthropocene epoch. Humans are changing Earth’s near-surface environment at a pace that may be unprecedented in more than 4.5 billion years of Earth history.
46. The Next 5 Billion Years
In the next two lectures, explore events that will affect Earth in eons to come. Begin with the end stages of our planet, some 5 billion years in the future. Then look from 2 billion to 50 million years from now, which is more than enough time to erase our every trace.
47. The Nearer Future
Glimpse 50,000 years into the future, when the greatest geographical changes on Earth will come from rising and falling sea levels. Then look a mere century ahead, focusing on the likely effects of rising greenhouse gases. The rate of change, not change per se, is the biggest concern.
48. Coevolution of Geosphere and Biosphere
Review the 10 stages of mineral evolution, from the solar nebula to the rise of animals with mineralized skeletons. Are we now entering an 11th stage? Close by considering an example of the coevolution of life and minerals in a remarkable formation on the shores of the Chesapeake Bay.
