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Doomsday for Dinosaurs - a melodrama in four acts


what makes a dinosaur a dinosaur?  


origin, evolution, diversity, abundance, and distribution


did any dinosaurs survive the asteroid impact? birds  


where do asteroids come from? 


how do asteroid impacts cause mass extinctions?  


how does climate change cause mass extinctions? 


what else came to Earth from space in the past?  


what other catastrophes caused mass extinctions?

Act I - 13.8 BY of Explosions, Catastrophes, and Mass Extinctions

9 BYs of cosmic evolution led to the violent birth of Earth and Moon and 700 MY Hadean eon

summary of the evolutionary history of the universe

  • Energy and matter evolved in the first few minutes of our expanding homogeneous universe
  • Dark matter preserved primordial quantum density fluctuations before the universe was cool enough for ordinary matter to condense to form a cosmic web of stars and galaxies
  • Ordinary matter was attracted to the dark matter cosmic web when the expanding universe cooled
  • The first stars were massive, short-lived, and had none of the building blocks for rocky planets or life
  • Supernovas synthesized and dispersed the building blocks for later generations of less massive, long-lived stars with rocky planets and the ingredients and conditions for life to evolve
The Milky Way galaxy began to form 13 billion years ago when small galaxies began to merge. The sun formed 4.6 billion years ago when a distant supernova explosion squeezed the pre-solar cloud of swirling gas and dust together. Most of the mass was captured by the sun, but the faster moving components stayed in orbit forming planets, dwarf planets, moons, comets, and asteroids in our solar system.
The Earth and Moon also formed about 4.5 billion years ago, and for the next 500,000 years, Earth was a molten mass covered in lava and constantly peppered with meteors, which is why scientists call this era the Hadean – named after Hades, the Greek god of the underworld. The atmosphere was almost all carbon dioxide, and though liquid water started forming on the planet surface, it was far from habitable.

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the sands of time recorded the 4 BY evolutionary history of life on Earth that began in the Archean eon

Roughly 4 million years ago, the Earth cooled and its surface hardened and broke up into the tectonic plates. Oceans formed, too. During the next 1.5 million years, an era called the Archean, the first life appeared on Earth, though the atmosphere was chock full of toxic methane and ammonia gases. The oldest lifeforms to date are 3.7 billion-year-old bacteria called stromatolites that performed photosynthesis – the process of changing carbon dioxide, water, and sunlight into oxygen. Stromatolites, along with another photosynthetic organism called cyanobacteria, started pushing oxygen into the toxic atmosphere.

The sands of time record the evolutionary history of the Earth and life. Recent deposits of sediments bury earlier deposits. The earliest history is buried the deepest and so our history starts at the bottom of the diagram. The 4.5 billion year history of the Earth began when the universe was nine billion years old.

It consists of four geological eons: Hadean, Archaean, Proterozoic, and Phanerozoic.

Earth was uninhabitable in the Hadean Eon due to hellish conditions including the late heavy bombardment of space rocks.

The Archaean Eon saw the origin of life in its earliest and simplest forms, possibly triggered by conditions created by asteroid impacts.

The two billion long Proterozoic Eon saw the development of most of the molecular and metabolic processes necessary for complex life and it ended with the Cambrian explosion of complex organisms that left a rich fossil record in the sands of time.

The Phanerozoic Eon began when the Cambrian explosion kicked off the Paleozoic era 541 MYA. Most groups of large animals evolved within 25 MY on a planet that was already 4 BY old.

It wasn’t long before the first of five global catastrophes led to mass extinctions as the Ordovician Period ended with the extinction of many of the trilobite species that had only evolved 100 million years earlier. The Devonian Period ended with the extinction of more trilobites and many fish 80 million years later.

The Permian extinction killed off all remaining trilobites and many marine species and insects and amphibians. What followed was the Mesozoic era evolution of reptiles, dinosaurs, and mammals. 50 MY later, the Triassic Period ended with the extinction of many reptiles and enabled dinosaurs to diversify throughout the Jurassic Period.

The asteroid strike at the end of the Cretaceous Period ended the Mesozoic era reign of dinosaurs 66 MYA. Many marine animals also went extinct. Within a million years of the start of the Cenozoic era, many massive and diverse mammals evolved from their small ancestors.

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the 20 MY Cambrian explosion ended the Proterozoic eon and led to Phanerozoic eon mass extinctions


But it wasn’t until the post-Archean era, known as the Proterozoic, that Earth started to shape up. The first continents formed, and during this 2 billion year-long era, stromatolites and cyanobacteria became more common and widespread. These photosynthetic bacteria made so much oxygen that the atmosphere shifted from being almost all methane to being at least 15% oxygen, much like it is today. As that oxygen level went up, more and more multicellular organisms evolved, including the first fungi 1 billion years ago. Without that oxygen, complex life – humans, dinosaurs, birds, plants, cats – would not have been possible.

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biological evolution led to Paleozoic era extinctions; asteroids and volcanoes led to Mesozoic extinctions


250 million years ago, life on Earth was about 3.5 billion years old. Bacteria, algae, fungus, plants, and animals evolved throughout the lands and waters. Invertebrates were diverse and abundant. Vertebrates included fish, amphibians, and reptiles. Dinosaurs, mammals, and birds had not appeared yet.

The Proterozoic was followed by the Paleozoic, which lasted from 540 million years ago to when the first dinosaurs showed up 251 million years ago.
Life on Earth diversified quickly during the Paleozoic’s first 50 million years. Scientist call this “the Cambrian explosion,” when the predecessors of modern-day insects and crabs, corals, and the first creatures with spinal cords evolved deep with the world’s oceans. Trilobites and early fish scuttled around under the waves until the first lizard-like creatures moved onto land about 400 million years ago. By that time plants like ferns and trees had developed, too.
Spiders, cockroaches, lizards, snakes, and ancestral crocodile called archosaurs (which would eventually give rise to dinosaurs) flourished, and coniferous trees dominated the landscape.
But the Paleozoic was not without set-backs. Just before the rise of the dinosaurs, about 252 million years ago, the Earth’s climate changed rapidly due to volcanic eruptions in what is now Siberia. Those eruptions clogged the atmosphere with carbon dioxide, which warmed the planet and its oceans rapidly. Warmer waters hold less oxygen, so 90% of marine life suffocated. Many marine creatures including trilobites and some corals, went extinct, along with 70% of land-based species. This is known as the Permian extinction.

Act II - What Really Happened on Doomsday 66 MYA?

an extraterrestrial attack unexpectedly made a big splash



visualization from Discovery channel visualization



But the reign of the thunder lizards was not to last. It was all done undone by a giant space rock.

About 66 million years ago, an asteroid struck near modern-day Mexico. Named Chicxulub [pronounced chick-soo-lube], which means “flea devil” in the local Maya language, this 6-mile-wide asteroid hit Earth at a speed of 12 miles per second (or 43,200 mph … that’s about 30 times faster than the speed of a supersonic jet).

The asteroid almost immediately incinerated dinosaurs within a 1,000-mile radius. Some scientists estimated its power was equal to 10 billion atomic bombs used during WWII. After it hit, wildfires spread out from the impact site; some started hundreds of miles away. It drilled a hole 12 miles long and 100 miles wide, and water displaced by the rock hitting the ocean formed a quarter-mile-high tsunami, that reached as far as modern-day Illinois.

But the real trouble was the amount of rock and sulfur the impact thrust into the atmosphere. Some 357 billion tons of sulfur went skyward, and eventually blocked the sun for decades. Without ample sunlight, the Earth cooled.

So while some scientists once thought the dinosaurs may have perished due to volcanic eruptions kick-started by the asteroid’s impact, or perhaps died of a resulting global plague, researchers now agree that the dinosaurs – and 75% of life on Earth – eventually froze to death.


the shock wave incinerated life a thousand miles away and triggered earthquakes and volcanoes



The immediate impact was extraordinary.

It turns out the asteroid hit at precisely the right angle to inflict as much damage on the Earth and its inhabitants as possible. When an asteroid drops straight down into the Earth, it vaporizes fewer rocks and releases less gas. But Chicxulub hit a sulfur-rich area of the Earth’s surface at a 60-degree angle, which meant it kicked the maximum amount of sunlight-blocking sulfur and carbon dioxide into the atmosphere. That caused an immediate, planet-wide winter that the dinosaurs couldn’t survive.

That sulfur caused a torrent of acid rain that fell into the surrounding ocean, making the water more acidic and killing all plankton under the waves. Without those plankton, the marine ecosystem collapsed and a majority of ocean species went extinct.

Flying reptiles, like pterosaurs, and swimming reptiles, like mosasaurs and plesiosaurs also disappeared. Most mammals larger than rats died, and 50% of plant species were wiped out. The age of giant reptiles was over after one asteroid changed the planet’s destiny forever … and paved the way for mammals, including modern humans, to evolve.


the asteroid struck at the right time and place to have an impact exceptional for its size





sulfur and dust blocked the sun and collapsed the food web causing mass extinctions on land and sea



While the dinosaurs froze, volcanic eruptions near the equator pushed more carbon dioxide into the atmosphere. This greenhouse gas acts like an insulator, trapping heat close to the planet and warming it. That resulting warming made it possibly for some of the hardier species – like birds and mammals – that survived the winter after the impact to start rebuilding Earth’s ecosystems in the equatorial region. Many small mammals (ancestors of the species that roam the planet today) survived the heat of the impact and following cold spell because they lived underground in burrows or in fresh water environments.

The asteroid and its aftermath killed most of the world’s forests, making it almost impossible for tree-dwelling birds to survive. But some of the birds that lived on the ground persisted, relying on grains and seeds to survive. Once the forests and plant life grew back, those birds colonized the treetops again and evolved into modern bird species.


Act III - Mesozoic Era Reptiles, Dinosaurs, and Mammals Compete

before Pangaea split into separate continents, reptiles and their descendants were free to roam everywhere




archosaurs on the reptile family tree evolved and thrived in Triassic period





dinosaurs dominated the planet during the balmy conditions of the Jurassic period


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the Cretaceous period breakup of Pangaea led to great dinosaur diversification





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Act IV - The surprisingly Happy Ending

within a million years, the smallest mammals evolved to dominate the planet


In the 1,000 years following the asteroid strike, fossil records show only tiny rat-sized creatures eked out a living amid the surviving plant life. Ferns were plentiful, but not much else. By 100,000 years post-impact, mammal populations had doubled and they were now the size of raccoons, living among palm trees rather than ferns.
Some 300,000 years after Chicxulub, plants that bore nutritious foods like walnuts, had returned. Those nuts enabled new mammals to evolve and diversify, and the creatures reached the size of beavers.
Another 400,000 years later, legumes like peas and beans came back, mammals grew to 100-pound sizes munching on those peas, and forests returned.
But researchers found it ultimately took 4 million years for South America’s and 9 million years for North America’s biodiversity to fully recover.


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adaptive radiation produced the variety of mammals seen today on the land, at sea, and in the air

The era following the asteroid strike is known as the Cenozoic, and we’re still living in it today. It’s also known as the age of mammals, which thrived (over a very long time) in the biological void left by the dinosaurs’ extinction and eventually grew to the large sizes we see today.
Nearly every plant alive today prospered during the Cenozoic era, including grasses, edible crops, flowering plants, and pine trees. Early horses, mammoths, saber-toothed cats, giant prehistoric mammals like sloths and rhinos first dominated the landscape before giving way to modern-day cats, dogs, elephants, and pigs. Primates arose, along with cattle-like species including cows, goats, and sheep. Marsupials flourished in the Southern Hemisphere.

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the branches of the tree of life co-evolved and diversified throughout the Cenozoic period

Marine species likes crabs, sea stars, and shrimps – known as invertebrates – diversified in the Cenozoic too, and squid thrived. As the continents drifted further and further apart, finally taking their modern places on the globe, the oceans widened and marine species like whales and sharks multiplied to take the place of the now extinct mosasaurs and plesiosaurs.

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will the next catastrophe end the Cenozoic period or the entire Phanerozoic eon?

While the Earth has since bounced back from the mass extinction that killed the dinosaurs, scientists agree the planet is now in the midst of another, sixth, mass extinction caused by human activity. During the last Ice Age, humans hunted some giant mammals, including sloths and mammoths, to near extinction. In the last century, hundreds of species have gone extinct due to habitat destruction and man-made global warming.

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