Extremely Rare And Fragmentary Fossils

We have come a long way in understanding the intricate history of the Earth and its sibling rocky planets. We have found that orbital dynamics, geology, chemistry, and biology are intertwined. The glue that binds these elements together, and shaped the trajectory of our Solar System, is interplanetary collisions. At the dawn of the Solar System, collisions were responsible for the growth of the terrestrial planets, and later, collisions modulated their evolution. The most violent collisions tear apart planets and form moons. New worlds emerge from the upheaval of cosmic catastrophes like the mythical phoenix reborn from its ashes. There was a time, early in Solar System history, lasting perhaps several hundred million years, when collisions ruled. The energy unleashed would have boiled away oceans, and generated massive earthquakes, followed by the outpouring of vast amounts of lava across the surface. For long stretches of time, a dense and dusty atmosphere obscured the Sun by day and made the nights starless. The sky and the Earth were united by a thick haze. The Moon, still close to Earth, loomed large. This vision is based on imagining the early Earth as scientific evidence tells us it must have been, but myths from ancient civilizations from all over the world curiously depict a similarly chaotic beginning.

You Haven't Done Nothing

The titanomachy myths from ancient Greece perhaps best portray this primordial chaotic evolution. Hesiod’s Theogony listed twelve Titans. Uranus feared his children and confined them in Tartarus, the dark abyss of the Earth. Gaia, indignant, spurred her children on against the unjust Uranus. Cronos lay hidden holding an iron sickle and at the propitious moment cut off his father’s genitals with a single, powerful stroke. Cronos took his father’s throne and for untold ages governed with Rhea over heaven and earth. In time, fearing that his children would dethrone him, as he had done to Uranus, Cronos turned cruel and unjust, like his father before him, and decided to swallow his own children. Earth, sea, and sky were a seething mass, and long tidal waves from the immortals’ impact pounded the beaches, and quaking arose that would not stop. Borrowing again from titanomachy myths, we could call this epoch Machean, the time of battle, the eon in which massive clashes took place. As in ancient Greek mythology, each terrestrial planet has its own character and fate. Mercury’s surface might have been entirely wiped out around 4 billion years ago.3 On Earth, life tentatively took hold sometime during the first billion years, setting the stage for drastic environmental changes, with the buildup of atmospheric oxygen from about 2.5

The Narrow Way

billion years ago, that led to our rich biosphere capable of sustaining a great variety of complex organisms. These environmental changes were triggered or modulated by frequent collisions, and one has to wonder how our planet would have fared had they not happened. Collisions are commonly regarded as purely destructive. It appears entirely possible that collisions could have been beneficial to the development of the Earth as we know it. Collisions are a means of bringing together different ingredients and creating new possibilities. This reminds me of human migrations, a social phenomenon dear to me, as I am a migrant too. Ancient peoples journeyed from one place to another, pressed by need, seeking better pastures, or driven by greed and the urge for conquest. In his bestseller Guns, Germs and Steel, the American anthropologist Jared Diamond refers to the European invasion of the Americas as hemispheres colliding. Old World and New World societies had developed largely in isolation, metaphorically as two distinct worlds. The clash of these societies was dramatic, with repercussions that are still open wounds today. In the long term, one hopes, this intercultural and interracial mixing has the potential to result in the creation of new and more diverse societies. Interplanetary collisions operate in a similar way.

Friday On The Mind

Local havoc is generated when two planets slam into each other, but at the same time, these events are capable of planting the seed of a beneficial turn of events to follow. I like to call the full spectrum of consequences of collisions creative destruction. The destructive nature of collisions is evident. No one would disagree that if a large asteroid were to collide with the Earth today, we would be in deep trouble. The creative aspect, however, is more subtle and often neglected even by scientists. Where would we be, had no massive collision early in Earth’s history brought in and made available the key elements for life? This is no conclusion based on abstract theoretical models. Quite simply, we humans likely would not be here had no collisions happened throughout the history of the Earth. This is surely almost certainly true with regard to the big collision 66 million years ago in what is now the Yucatan peninsula, which caused the dinosaurs to go extinct and gave the mammals their chance. Scientists keep unraveling more intriguing details to this amazing story. Still, it is unclear if there was a single, specific trigger for the global extinction of about 75 percent of living organisms on Earth. Scientists are determined to find out. Two independent teams of researchers studied in detail the ways in which a localized event, especially a very energetic one such as the Chicxulub collision, could have affected both land and marine biospheres across the globe. In a paper published in 2019 by the Proceedings of the National Academy of Science,5 an international team of researchers studied in detail the changes in marine chemistry around the time of the extinction. This acidification would likely be due to the rainout of sulfur, nitrogen, and carbon species released into the atmosphere by the collision. This relatively sudden change in ocean chemistry could have been enough to trigger a marine biosphere collapse at the base of the food chain. In a domino effect, all the animals higher up the food chain would die off. The discovery of new fossils over the past decade in China, Brazil, and other localities shows that mammals underwent significant diversification while coexisting with dinosaurs, but they generally remained relatively small.