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---------------------1894 - Asteroid impacts in Earth‘s evolution.
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- There is no question that asteroid impacts have significantly affected Earth’s history and the evolution of life on the planet. Science has found evidence of 17 impacts older than 2,500 million years. There could have been hundreds more of these impacts that have been hidden in major tectonic shifts and extensive magma flows.
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- The Moon’s surface shows evidence of monster rock bombardments back to 3,900 million years ago. New evidence on Earth is found in seafloor sediments that date back 3,460 million years. The massive impacts vaporize the asteroid instantly, forming tiny spherical glass particles called “ spherules”.
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- The ocean sediments were preserved by two layers of volcanic sediment that could be radioactive dated with high precision. The levels of platinum , chromium, and nickel found in the spherules are the same as found in asteroids.
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- The largest impact occurred shortly after the Earth was first formed. It occurred 4,500 million years ago when an asteroid the size of a small planet slammed into the Earth splashing surface debris into orbit. The Earth -crust that was launched eventually accreted and coalesced into the Moon.
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- This scenario is evidenced by the zinc isotopes on the Moon matching those in Earth’s crust. Also, lunar rocks returned from the Apollo Mission had the same ratios of oxygen isotopes as those on Earth.
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- Later impacts were on smaller scales, thankfully. The Sudbury Basin in Ontario, Canada is one of Earth’s largest craters, 160 miles in diameter, 9.3 miles deep, that occurred 1,800 million years ago.
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- The Chicxulub impact in the Yucatan Peninsula occurred 66 million years ago. It was 110 miles in diameter. This impact is credited with wiping the dinosaurs off our evolutionary record.
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- The Meteor Crater near Flagstaff, Arizona was created by an iron meteorite 150 feet in diameter. This impact occurred just 50,000 years ago.
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- On February 15, 2013 the 10,000 ton meteor exploded 18 miles above the Russian country side near Chelyabinsk.
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- No question asteroids greatly influenced our past. Dinosaurs did not survive. Somehow mammals did. Their story fits in the midst of all this.
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- In 1824 the Geological Society of London announced the discovery of the first dinosaur. In that same stone quarry another discovery, two tiny mammal jaws the size of a mouse jaw.
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- Were mammals living with dinosaurs? Yes! Mammals defined as having fur, mammary glands, big brains , complex teeth, and keen senses. Placental giving birth to live, well-developed young. These mammals numbered among the 5,000 species living on Earth at that time.
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- The earliest traces of prehistoric mammals are dated 210 million years ago. Mass extinctions marked the end of this period. Turtles, lizards, frogs, crocodiles and small dinosaurs that eventually became birds managed to survive. Also discovered were small shrew-to-mouse sized mammals that survived after 90% of mammal species died out with the dinosaurs.
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- A distinguishing feature in these first mammals, was baby teeth being replace with adult teeth. This feature allowed youngsters without teeth to nurse on the mother’s milk. This allowed mammals to grow faster and the young to have a better chance of survival.
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- Mammals grew huge brains compared to their ancestors. They also grew larger olfactory bulbs to smell and auditory to hear. These small animals had powerful jaws to crush the exoskeletons of insects. The could slice and grind small plants. During the 252 million to 66 million year era dinosaurs ruled while these small animals existed on small insects and scurried underground. Their sharp senses, fine-motor skills, elevated metabolism, enabled them to thrive in the cold and dark of night.
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- 160 million years ago lived a dog-sized creature with webbed hands and feet and a flattened tail like a beaver. There were flying squirrels gliding through the trees. Between 174 to 164 million years ago the number of mammal species increased dramatically. Flowering and fruit bearing trees became a new source of food for them.
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- 66 million years ago an asteroid struck the Yucatan and unleashed wild fires, tsunamis, earthquakes, and volcanic eruptions. The longer term climate and environmental changes extinguished the dinosaurs that had survived the previous 150 million years. Some of the earliest mammals survived. Placental evolved quickly evolving to fill the available niches.
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- 63 million years ago a puppy-sized creature with gangly limbs, long fingers and toes was leaping through trees. This is the oldest known primate. It took another 60 million years to become a bi-pedal walking ape. Just 3 million more years of evolution and I am sitting here writing about it.
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- The large asteroids of our past have been a major contributor to the evolution of life on Earth. What about our future? Astronomers have identified more that 12,000 asteroids in near-Earth orbit. Only 1,000 of these have been characterized as to composition, size, shape, and rotation speed.
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- It makes a huge difference whether an Earth- threatening asteroid is solid rock or a pile of rubble. Not just in case we have to divert it, but, also just learning composition helps us understand how the Solar System was built.
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- The smaller objects become visible only with a few days of their closest approach and with a miss we have only a few weeks to characterize them. The fast spinners are likely to have a solid dense interior. The fastest spinning asteroids, some 20 meters in diameter have spinning rotations of 16 rotations per second.
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- Knowing spin and composition are critical if astronomers have to redirect an asteroid’s trajectory. Scientists are characterizing only 100 near-Earth asteroids a year but discovering as many as 1,400 per year.
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- Will asteroids continue to influence life and evolution on Earth? Time will tell. What about all those exoplanets in another solar systems? What kind of evolution are they experiencing? Time will run out before I will know.
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- Request Review #1866 to learn about evolution and supernovae. Plus this review lists 5 more reviews on the subject of evolution.
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