Dinosaur Killers

by Popoff, Alexander

  “From darkness. The impact created huge amounts of dust, cutting off the sun’s power by up to 20% for 8 to 13 years.”

  Actually, the “dark times” lasted much longer, about 100,000 years, and started a long time before the impact events.

  In their article “Extraterrestrial amino acids in Cretaceous/Tertiary boundary sediments at Stevns Klint, Denmark,” published in the journal Nature in 1989, Meixun Zhao and Jeffrey L. Bada reported that they had found isovaline and aminoisobutyric acid tens of centimeters below and above the K-Pg boundary. The authors surmised that the collision of a massive extraterrestrial object with Earth may have produced this unique organic chemical signature because certain meteorites contain organic compounds which are either rare or nonexistent on Earth. Zhao and Bada suggested that the extraterrestrial amino acids diffused from the boundary clay above and below it. In the boundary clay itself, there are no amino acids.

  According to the research data, the entire boundary zone—a roughly 100-cm layer encompassing both sides of the boundary—which represents the catastrophic events, was formed for about 100,000 years.

  The thin 1-cm boundary-layer clay is approximately in the middle of the boundary zone.

  In 1990, Kevin Zahnle and David Grinspoon of the NASA Ames Research Center suggested that the amino acids had been deposited for about 20,000 to 100,000 years by cometary fine dust.

  Max Wallis from Cardiff University argues that cometary dust delivered nonterrestrial microfungi or novel genes that were incorporated into existing micro-fungi on Earth and they produced the amino acids.

  Edwin Olson hypothesized in his article “Coal conversion at the K/T boundary: Remnants of the Hazardous Waste” that the amino acids could partially originate from a natural coal-gasification process involving the intrusion of magma into the coal seam.

  The first question we should settle here is whether the amino acids in the boundary zone are terrestrial or extraterrestrial, and what is their origin—biological or nonbiological?

  Isomers are substances composed of the same elements in the same proportions but that differ in properties because of differences in the arrangement of atoms. Every amino acid (except glycine) can occur in two isomeric forms.

  The amino acids in the boundary zone are in both D and L forms. L and D forms of amino acids are mirror images of each other, but they can’t superimpose. Chirality is astructural characteristic of a molecule that makes it impossible to superimpose it on its mirror image. Human hands are a universally recognized example of chirality: The left hand is a non-superimposable mirror image of the right hand.

  Only L-amino acids are manufactured in the organisms and incorporated into proteins. Some D-amino acids are found in the cell walls of bacteria but not in bacterial proteins.

  In chemistry, a racemic mixture, or racemate, is one that has equal amounts of left- and right-handed forms of a chiral molecule.

  Amino acids formed from nonbiological processes occur in racemic mixtures.

  The amino acids in meteorites and in the K-Pg boundary zone contain both D and L forms.

  The equal quantities of the L and D forms of the amino acids in the boundary zone are evidence of their nonbiological origin. And they are extraterrestrial—they are mixed up with extraterrestrial molecules like iridium and follow the same peak enrichment pattern within the boundary zone.

  Isovaline and aminoisobutyric acids are common in meteorites but rare in the biosphere.

  Of course, the K-Pg amino acids could originate from a natural coal-gasification process, but the produced quantities are not significant and they can’t be deposited worldwide. Another problem with the amino acids that could originate from a natural coal-gasification process is why the hypothetical natural gasification stopped producing them exactly at the time of the formation of the boundary-layer clay itself? The natural gasification produced amino acids before the impact; during the formation of the boundary clay it stopped, then the natural gasification started again. And, what is really strange, why did it follow the enrichment pattern of the iridium before the impact and after the impact?

  Asteroids can’t perform the trick of delivering amino acids, iridium, and other substances for tens of thousands of years before and after the impact.

  The asteroid and volcano theories, which are prevalent among scholars, can’t explain the presence of the amino acids and the iridium and their spikes before and after the boundary, and how they were deposited for about 100,000 years in the boundary zone.

  In short, K-Pg mass extinction theories that can’t explain the presence of uncommon amino acids and iridium above and below the Cretaceous-Paleogene boundary are not viable.

  The detailed analysis of the K-Pg boundary layer and the boundary zone (the 100-cm layer encompassing both sides of the boundary) rejects the possibility that they could be formed by an asteroid impact or volcanic activity, and provides clear evidence that there was a comet impact.

  The K comet

  Long-period comets have highly eccentric orbits, extending to the far reaches of the Solar System, and periods ranging from 200 years to thousands or even millions of years.

  Sometimes they make close passages by the planets and the Sun, diverting into the inner Solar System and becoming short-period comets.

  Short-period comets are comets that have orbital periods of less than 200 years. Their orbits typically take them out to the region of the outer planets—Jupiter and beyond.

  When comets approach the inner Solar System and the Sun, they begin to sublimate (cometary material transits directly from solid state to gas) and vaporize, creating an envelope of thin gas and fine dust called coma. If a comet comes very close to the Sun, it is heated to about 2,800 degrees Celsius (5,000 degrees Fahrenheit); it is hot enough to vaporize not only ice and gases but also rock and metals. The original comet becomes smaller, sometimes much smaller, due to the loss of cometary material. But not all comets come so close to the Sun.

  The K comet didn’t get too close to the Sun because the amino acids survived and were deposited on Earth’s surface.

  Sungrazing comets come within a few million kilometers of the Sun before turning around and heading in the other direction.

  Sunlight pushes the gas and the dust of the comet away to form a tail.

  A comet is exhausted or extinct when most of the volatile material contained in the nucleus evaporates away by the Sun, and the comet becomes a much smaller, dark, inert lump of rock or rubble that can resemble an asteroid.

  Comets may go through a transition phase as they come close to extinction. A comet may be dormant rather than extinct if its volatile component is sealed beneath an inactive surface layer. Scientists suspect that some asteroids were once comets. A comet loses part of its mass with each passage around the Sun.

  The main difference between an asteroid and a comet is that a comet shows a coma due to sublimation of the cometary material by solar radiation. Some or perhaps most comets are eventually depleted of their surface volatile ices and gases and become asteroids. A further distinction is that comets typically have more eccentric orbits than most asteroids. Most “asteroids” with eccentric orbits are probably dormant or extinct comets. Comets are formed in the outer Solar System. Asteroids are formed in the reservoir between Mars and Jupiter.

  Researchers think that about 6 percent of the near-Earth asteroids are thought to be extinct nuclei of comets that no longer experience outgassing.

  Comets interact gravitationally with the Sun and other objects in the Solar System. Their orbits are primarily but not completely determined by gravity because their motion through space is also influenced to some degree by gases jetting out of them. Some comets change their orbits several times during their lives.

  There have been thousands of comets but only around 190 are classified as periodic. The most famous periodic comet is Halley’s comet, returning every 76 years.

  There are many mechanisms that limit the lifetime of a comet. Short-period comets in
the inner Solar System typically have a lifespan of only thousands to tens of thousands of years.

  The mean life of a long-period comet is about 600,000 years.

  Halley’s Comet passes the Sun once every 75 years, and it will be completely sublimated and disappear after only 10,000 years or about 100 rotations around the Sun.

  If short-period comets don’t get close to the Sun or/and they are large, their lifespan is much longer—about 100,000 years.

  The size of the original K comet was more than 100 km in diameter, probably 300 to 400 km. The K comet became a short-period comet with a life span of about 100,000 years.

  Comet Hale–Bopp was perhaps the most widely observed comet of the 20th century. Analysis indicated later that its comet nucleus (the solid, central part) was approximately 60 kilometers in diameter.

  The Comet of 1729, also known as Comet Sarabat, is considered to be potentially the largest comet ever seen, with a cometary nucleus of the order of 100 km in diameter.(The comet was discovered by Fr. Nicolas Sarabat, a professor of mathematics, in 1729.)

  Comets could be much larger than these dimensions, reaching diameters of thousands of kilometers.

  Pluto is no longer considered a planet in the Solar System. “Pluto, being half ice by volume, should assume its rightful status as the King of the Kuiper Belt of comets,” said Neil Tyson, director of the Hayden Planetarium at the American Museum of Natural History.

  Pluto’s size is tiny for a planet but huge for a comet. Its diameter is approximately 2,280 kilometers (1,420 miles). Pluto is the only “planet” to travel an elliptical orbit like a comet.

  Haumea is a minor planet located beyond Neptune’s orbit. The most likely shape is a triaxial ellipsoid with approximate dimensions of 2,000 x 1,500 x 1,000 km.

  A huge swarm of Pluto-like objects beyond Neptune is known as the Kuiper Belt, after Gerard Kuiper. Astronomers estimate that there are at least 35,000 objects in the Kuiper Belt greater than 100 km (62 miles) in diameter. There never will be a shortage of large comets entering the inner Solar System, and threatening the Earth.

  Researchers reported that there are no enhanced levels of helium-3 before and after the K-Pg boundary. Some scholars suggested that the impact at the end of Cretaceous was not caused by a comet but by an asteroid because the cometary dust would saturate the K-Pg boundary zone with helium-3.

  Helium-3 is an isotope of helium with two protons and one neutron. It has one less neutron than regular helium and is produced in the Sun. Helium-3 is emitted by the Sun within its solar winds. The solar wind is a stream of charged particles (a plasma) released from the upper atmosphere of the Sun. The solar wind streams off of the Sun in all directions at speeds of about 400 km/s.

  The stream of particles from the Sun (solar wind) contains helium-3, which saturates the surface of the space bodies and the cosmic dust in the inner Solar System.

  However, cometary particles, part of the tail, and the coma could dust the Earth before being saturated with helium-3 because they are forming continuously from the core; they don’t spend too much time in space, and the K comet didn’t approach close to the Sun.

  The helium-3 saturation of interplanetary dust particles (IDP) depends on how long they were saturated by the solar wind and how far the objects are from the Sun.

  Researchers have reported there is no helium-3 on Mars, which is farther than Earth and the Moon. Even if there is some helium on Mars, the amounts would be very low. The quantity of helium-3 on the Moon is high enough to allow mining. Now countries are preparing for a new space race to harvest helium-3 for clean nuclear fuel. The Moon was saturated with helium-3 for billions of years.

  Scientists found out that fresh cometary dust particles have very low abundances of solar noble gases, including helium-3.

  “Dust particles in space at 1 AU have their surfaces saturated with implanted solar wind on a timescale of a few decades. Particles in orbits typical for short-period comets will require ~5x longer to become saturated,” wrote Scott Messenger in his article “Opportunities for the stratospheric collection of dust from short-period comets,” published in 2002 in Meteorics & Planetary Science.

  One AU is approximately 150 million km (93 million miles) or roughly the mean Earth–Sun distance.

  According to Messenger, “Dust from these comets is directly injected into Earth-crossing orbits by radiation pressure, unlike the great majority of interplanetary dust particles collected in the stratosphere which spend millennia in space prior to Earth-encounter. Complete dust streams from these comets form within a few decades, and appreciable amounts of dust are accreted by the Earth each year regardless of the positions of the parent comets. Dust from these comets could be collected in the stratosphere and identified by its short space exposure age, as indicated by low abundances of implanted solar-wind noble gases.”

  The average lifetime of dust near Earth’s orbit is approximately 10,000 years.

  There are now 17 currently active Earth-crossing comets. The term Earth-crossing comet means a comet on an orbit that as a consequence of perturbations can intersect the orbit of the Earth. And, of course, hit our planet.

  Researchers reported that there are no enhanced levels of helium-3 before and after the K-Pg boundary. Correctly interpreted, this gives us important information about the nature of the K comet and the mechanism of the impact. It suggests, first, that Earth passed many times through a cloud of fresh cometary dust, not through a cloud that was in the inner Solar System for thousands of years or longer and, second, that the comet at some point fragmented and a large chunk catastrophically hit our planet. The rest of the fragments continued to intersect the orbit of the Earth and dusted our planet with fresh cometary particles for tens of thousands of years.

  Before entering the inner Solar System, comets are not saturated with helium-3 because of the huge distance from the Sun. Even when they enter the inner Solar System, most of the time they are much further than Earth’s orbit. Comets spend only a small fraction of the time close to Earth’s orbit. Some comets have specific orbits—low eccentricity and low inclination orbits with nodes very close to 1 AU.

  These comets don’t come close to the Sun, but only to Earth’s orbit. Their dust particles need much more time to be saturated with helium-3 because they stay far away from the Sun.

  Most the dust spends thousands, even hundreds of thousands of years, in the Solar System and is heavily saturated with helium-3. Virtually all particles dusting the Earth, excluding the fresh ones, spent about 100 to 100,000 years in space.

  The K comet was nearly on a collision course with Earth, and the cometary dust spent only a very short time in space before being deposited on Earth, having no time to be saturated with helium-3.

  There are several peaks of iridium and extraterrestrial amino acids before and after the boundary layer. They possibly could be caused by fragmentation of the comet, hence the increased levels of cometary dust. Maybe there were also airbursts of smaller fragments of the comet before, during, and after the main impact.

  After the first fragmentation of the K comet in space, a swarm of cometary dust and fragments was orbiting, and its number was becoming larger and larger with each fragmentation.

  Comets are in unstable orbits that change over time due to perturbations and outgassing.

  Comets bypassing Earth in a specific orbit deliver fresh cometary dust that is only very slightly saturated with helium-3. Scott Messenger and his team from Washington University identified and researched four such comets.

  Zahnle and Grinspoon suggested that, “Dust remained in orbit after the impact, and so continued to [be] swept up for a few thousands or tens of thousands of years.”

  However, the K comet was in a specific short-period orbit so that the cometary dust particles were not saturated with helium-3 by the solar winds. The dust deposited on Earth was fresh. It didn’t spend a few thousands or tens of thousands of years in space.

  The absence of higher levels of helium-3
before and after the impact boundary just tells us that there was no cometary cloud in space that was exhausted by Earth when passing through it for tens of thousands of years.

  Zahnle and Grinspoon wrote, “The lesser amounts of AIB (aminoisobutyric acid) and isovaline above the boundary clay could be ascribed to loss of the source.”

  More likely, after a huge fragment or a few fragments of the comet collided with Earth, first, the total mass of the rest of the comet (fragmented or in one piece) became smaller and delivered lower and lower amounts of cometary particles into Earth’s atmosphere for about 30,000 to 50,000 years. And, second, it was partially exhausted; anyway, it dusted our planet for tens of thousands of years and lost a lot of cometary material.

  The K comet leftover fragments remained moving in Earth-crossing orbit until they were exhausted (100,000 years is a usual time for such a comet to become fully exhausted), destroyed via hitting the Sun or some other planet, left the Solar System, or continued their life as asteroids or dead comets.

  The amounts of helium-3 in the dust deposited on Earth depend also on the temperatures the cometary particles are heating to when entering the terrestrial atmosphere. Experiments showed that when interplanetary dust particles are heated to 630°C, about 50 percent of the helium-3 is released.

  IDPs are typically heated at temperatures higher than 500°C during their atmospheric entry.

  Cometary dust moves at higher velocities than asteroidal dust and the entry temperatures are higher. The higher the temperatures, the more helium-3 is released from the dust.

  The collected dust includes a large fraction of particles heating above 600 degrees C.

  The fresh cometary dust was not saturated with helium-3, and, even if there was some saturation, most of the helium-3 is released by the entry into the atmosphere because of the heating.

  The K comet broke up in space and subsequently its fragments impacted the Earth.