Alvarez hypothesis

The Alvarez hypothesis is a scientific theory about a massive event in Earth's history. It suggests that a large asteroid hit the planet and caused a mass extinction. This event wiped out the non-avian dinosaurs and many other living things. Scientists call this period the Cretaceous–Paleogene extinction event. It marks the boundary between two different geological ages. While many people once thought this happened 65 million years ago, newer research has changed that date. In 2013, Renne and his colleagues updated the timing to 66 million years ago.

The mechanism of this catastrophe involved a massive space rock hitting the Earth. Evidence shows the asteroid fell in the Yucatán Peninsula at a place called Chicxulub, Mexico. The collision released an incredible amount of energy. This energy was over a billion times stronger than the atomic bombs used in Hiroshima and Nagasaki. The impact was so violent it caused an earthquake of magnitude 10 or 11. Such a powerful shock would have caused seiches, which are oscillating movements of water in lakes or bays. In places like North Dakota, this caused a sudden burial of organisms under thick sediment.

Scientists have identified several specific effects caused by the impact. One major effect was the vaporization of gypsum, a rock containing sulfate. This rock turned into an aerosol, which is a tiny spray of particles, and entered the atmosphere. The dispersal of this dust and sulfate likely caused long-term changes to the global climate. These changes included large temperature drops that devastated the food chain. Another effect was the movement of deep Earth materials. A 2016 drilling project found that the peak ring of the crater contained granite. Since granite comes from deep within the Earth, the impact must have ejected it to the surface in minutes.

The history of this hypothesis began with a remarkable discovery in 1980. A team led by Nobel prize-winning physicist Luis Alvarez and his son, geologist Walter Alvarez, found something unusual. They were working with chemists Frank Asaro and Helen Vaughn Michel. They discovered that sedimentary layers around the world contained very high levels of iridium. Iridium is a metal that is rare on Earth but common in asteroids. This discovery led them to suggest the asteroid impact theory. Shortly after, Dutch paleontologist Jan Smit independently suggested the same idea.

Today, the evidence for the Chicxulub impact is very strong. In 2010, an international panel of 41 scientists reviewed 20 years of research. They officially endorsed the asteroid hypothesis and ruled out other theories like massive volcanism. A 2016 drilling project provided even more support. It confirmed that the impact was large enough to create a 120-mile peak ring. It also showed that the impact caused a massive megatsunami. This tsunami was large enough to leave behind the largest known layer of sand separated by grain size.

Despite the support, there is a famous debate known as the "dinosaur wars." Some scientists, such as Gerta Keller, argue that the Deccan Traps caused the extinction. The Deccan Traps are massive volcanic flood basalts in Western India. These eruptions covered about 1.3 million square kilometers. Keller suggests that rising ocean temperatures and acid rain from these volcanoes caused the extinction. She also argues that the asteroid impact happened much earlier than the extinction event. This debate has been very intense and has sometimes affected the careers of the scientists involved.

A newer theory attempts to connect these two major ideas. Researchers Paul Renne and Mark Richards suggest that both the impact and the volcanoes played a role. They propose that the asteroid impact actually triggered the most intense period of the Deccan eruptions. They calculated that the largest period of volcanic activity occurred 50,000 to 100,000 years after the impact. This theory explains how the eruptions might have prevented marine ecosystems from recovering after the initial impact. This shows how different geological systems, like space impacts and Earth's volcanoes, can interact to change life on our planet.