Lisa Randall’s book called, ‘Dark Matter and the Dinosaurs’ is a very interesting read. It is a nice book on dark matter and their importance in the creation of galaxies; and their role in the destruction of species too. The theories are a little speculative but is based on some clear and hard research. Dark matter makes up for 25% of our universe. The ordinary matter we know of makes up for only 4%. The rest 70-71% is made up of an exotic energy called the dark energy. The amazing thing is till now, there is no clue to the nature of the dark matter and energy, except the fact that dark matter has gravitational influence; and the dark energy is something which is causing the stars to accelerate away at an ever-increasing speed. It is kind of anti-gravitational in nature. Dark matter is interesting also in the sense that it helps in the formation of galaxies and stars. It is also speculated that it lies at the very edge of galaxies as concentrated stuff.
She then describes the structure of our solar system, which is in fact, much larger than expected. Uranus (and the recently ousted Pluto from our planetary system) is perhaps not the edge. The Oort clouds composed of icy small objects is at least a light year away from the Sun, but is still under its gravitational influence. This technically allows the Oort cloud to be the edge of the solar system. The Oort cloud icy solid objects are the source of the comets which are intermittently thrown off their unstable orbits and they pass towards the Sun. In the process, some of them even manage to hit the Earth, sometimes with disastrous consequences leading to extinctions. The meteor belt between the planets Mars and Jupiter is another source of the meteorites. There is a fine difference in the definitions of asteroids, meteors, meteoroids, comets, near Earth objects, but a general word is used for all of them. She takes great pains to explain these words in detail and the structure of the solar system. The description of Oort clouds is fascinating to say the least.
Most of the objects entering the Earth’s atmosphere are burnt away and a few are noted as meteor showers which make for an awesome display of lights. However, a few are very large and their impact can lead to severe changes in the Earth’s environmental patterns. A huge comet crashed on Earth with a diameter of about 16 kilometres and caused the extinction of dinosaurs which had lived almost for 66 million years. This happened about 60 million years ago. The extinction was called the K-Pg extinction and it is the fifth of the major extinctions in the lifespan of the Earth living species. The last extinction of almost 75% of the species in a short span of 30,000 years allowed the humans to come to the fore. The interesting findings of the author’s research is that there is a certain periodicity of these major extinctions, roughly 30 million years, and these are linked to comet strikes which are ejected from the Oort clouds beyond the pales of the solar system.
It is surmised that there is a disk of dark matter which is termed as DDDM (double disk dark matter), lying at the central plane of the galaxy. The milky way galaxy consisting of almost 100 billion stars (of which our Sun is a small insignificant star) is in the form of a flat disk extending for 1,30,000 light years’ edge to edge. However, the thickness of the galaxy is only 2000 light years. Dark matter also surrounds the galaxies as a part of the cosmic web. The milky way galaxy rotates around the galactic center. The circling around the galactic center also involves an up and down movement of the solar system around the central plane of dark matter. When the solar system crosses the central disk of dark matter, there are perturbations of the icy objects in the Oort cloud due to gravitational influences. Interestingly, the periodicity of crossing this central plane is roughly 30 million years or so. So, the connection between the dark matter presence in the galaxy and the extinctions on Earth at a periodic time is gently suggested. Of course, a lot of things need to be sorted out and proved. But, she makes her point very nicely.
The story of the study of craters especially the large one which caused the K-Pg extinction and presently identified as the Chicxulub crater is another fascinating story. The study of craters by geologists led to the linkage between meteors and crater impacts. Thus, came the interaction of physics and geology to explain the phenomenon of Earth formation; and the link of distant objects and energies in space to the growth and extinction of species on Earth.
There may be a long overdue meteor strike to earth or it may not come for another 30 million years, but the scary thing is; we simply cannot do anything with the present state of technology to prevent a big strike even if we happen to recognize it early. This part is not there in the book, but is generally the feeling of physicists. However, the only hope of humanity ever coming together would be in such an event where the entire human species is at threat. However, most would want better reasons for humans to come together.
The next is a reproduction of the Wikipedia article on the crater itself.
“The Chicxulub is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named. The date of the Chicxulub impactor, which created it, coincides precisely with the Cretaceous–Paleogene boundary (K–Pg boundary), around 66 million years ago. The crater is more than 180 kilometres (110 miles) in diameter and 20 km (12 mi) in depth, well into the continental crust of the region of about 10–30 km depth. It makes the feature the third of the largest confirmed impact structures on Earth; the impacting bolide that formed the crater was at least 10 km (6 mi) in diameter. The crater was discovered by Antonio Camargo and Glen Penfield, geophysicists who had been looking for petroleum in the Yucatán during the late 1970s. Penfield was initially unable to obtain evidence that the geological feature was a crater and gave up his search. Later, through contact with Alan Hildebrand in 1990, Penfield obtained samples that suggested it was an impact feature. Evidence for the impact origin of the crater includes shocked quartz, a gravity anomaly, and tektites in surrounding areas.”
The book is fascinating as it explores some new aspects and gives some brilliant insights into the cutting-edge physics of today.
RANDOM MUSINGS 