A well known but extremely poor, in my opinion, generalisation in pure science is that “biology is just applied chemistry, and chemistry is just applied physics." Physics, in this sense, stands at the top, framing the very fundamental laws that govern the workings of the universe in which we reside. (Folks would argue the extension – "physics is just applied mathematics," with mathematics reigning supreme, exploring all possibilities, even ones not grounded in our reality. But let us not jump into that rabbit hole now and stick to our own universe).

In the above "hierarchy", they haven't mentioned geology. Of course, why will they? It is, as they mock, (and again, an abomination of a claim –) "not a true science!" While physics is hyped and well-portrayed in sci-fi movies and pop culture and many a young mind has been enchanted into pursuing fields such as quantum physics or cosmology, representation of the earth sciences is abysmal at best. It is not even a part of most high school curricula! As someone interested in both physics and geology, I was curious to find out the reason behind such contrasting perceptions of the two fields. My quest to gain answers led me to some fascinating anecdotes of physicists being at odds with geologists and occasionally finding themselves on the wrong side!

You would be surprised to know that, as compared to other sciences, radical ideas in geology emerged and were accepted in the scientific community but recently. For example, orbital motions of planets were known, and the fundamental laws of electrodynamics and thermodynamics were established before one of the first estimates of the Earth's age was made in the mid 1800s (and the debate continued long into the mid 1900s, when finally the currently accepted value was agreed upon). The electron and the proton had been discovered, and Einstein had published his landmark paper on special relativity by the time Wegener gave the hypothesis of plate tectonics in 1912 (which was mostly neglected, or rather, ostracised, until the 1950s brought unquestionable evidence).

The biggest reason for this delay in acceptance was the fact that most concepts introduced by geologists ran against creationists and western religious beliefs of the time, especially with the earth turning out to be far older than what the Bible dictated. But more importantly (in our context), some physicists opposed the views of geologists from time to time as well. Here I present a few historic clashes, starting with the one between two giants – Lord Kelvin and Charles Darwin.

Age of the Earth

Charles Lyell's first book, 'Principles of Geology,' was also his most famous, most influential, and most important one. It is one of the earliest compiled works in the field, and the idea of uniformitarianism (that the laws of nature today and here are the same as those that applied in the past or at some distant place) introduced in the book inspired many. This included Charles Darwin. His theory, that gradual changes accumulating over a long period cause life to evolve, is principally uniformitarian. After all, the creationist perspective involves 'unnatural' elements – it does not accord with the laws of nature as we see around us now. Observing the diversity of life on earth and estimating the amount of time it would have required to evolve such a variety of forms by a gradual process, Darwin was convinced that the earth had to be hundreds of millions, or even billions, of years old.

On the other hand, Lord Kelvin took a shot at the problem, with the best-known physics of the time at his disposal. In the 1860s, he showed, based on the laws of thermodynamics, that the age of the Earth could be no more than 20 million years, an order of magnitude or two lower than the claims of Darwin and the leading geologists. Convinced by his result and a strong belief in the unquestionable validity of scientific arguments, Kelvin severely criticised Darwin and his theory of natural selection. He deemed Darwin's result to be 'unscientific'. Darwin retorted, calling Kelvin his "sorest trouble." He could not, however, discredit Kelvin's calculation. He passed away in 1882, uncertain about his life's work.

Kelvin wasn’t proven wrong until radioactive isotopes in old rocks were used to estimate their age. It turned out that Kelvin had missed out on the heat generated by radioactive sources deep inside the earth. Later calculations by other physicists, incorporating the new knowledge, progressively got the value closer to Darwin's expectation. In the 1940s, geologist Arthur Holmes provided his estimate of 3.35 billion years. This was around the time when the clash shifted from Kelvin to another physics giant – Edwin Hubble.

Age of the Universe

Until the 1920s, it was widely accepted that the Milky Way encompassed the entire universe and that the nebulae in the sky were clouds within the Milky Way. This view changed dramatically when Edwin Hubble showed that the Andromeda nebula (which we now know is its own galaxy) lay far outside the then accepted boundary of the universe. The revolutionary discovery changed our perception of the universe forever, marking the birth of modern cosmology.

Though not directly critical of the work of geologists the way Kelvin was, the results of Hubble's work conflicted with those of Arthur Holmes. The universe's age was extrapolated by measuring the galactic redshifts and plotting the velocity of galaxies against their distances from us. The slope of this plot, which looked like a straight line, was called the Hubble constant and its inverse gave the age of the universe. To everyone's utter surprise, that turned out to be 1.8 billion years – the earth was older than the universe itself!

The discrepancy existed for around a decade, and debates ensued over who was right. As years passed, the Hubble constant was measured with improving accuracy, and the calculations were refined. Meanwhile, measurements of isotopes in meteorites provided a more accurate picture of the age of the earth. Today, the accepted ages of the universe and the earth are 13.8 and 4.5 billion years, respectively.

The Young Sun paradox

Another perplexing conflict between physics and geology arose recently. On analysing the earth's early atmosphere (i.e. 3.8 billion years ago) using old rocks and minerals, it was evident that liquid water must have been abundantly present at the time. In 1972, however, George Mullen and Carl Sagan pointed out that according to well-tested models of stellar evolution and dynamics, the Sun would have invariably been 30% dimmer at the time than the effulgent ball of gas it is today, making it incapable of heating the earth enough for it to sustain liquid water. This is called the young sun paradox, and it is still unresolved, with various theories proposed attempting to explain it from the greenhouse effect to the role of albedo.

As we approach the modern era on this journey winding down the history and confrontations of the two fields, we notice a gradual but steady change. From a highly critical Lord Kelvin to the welcoming Carl Sagan, one of the pioneers in the search of life across the cosmos, a beautiful amalgamation of physics, chemistry, biology, and the earth sciences takes place, as our quest for knowledge takes us to evermore all-encompassing questions.

We hear stories such as that of the father-son duo, Luis and Walter Alvarez. Luis was a Nobel prize-winning physicist who was part of the Manhattan Project that built the United States' first atomic bomb, while his son Walter was a geologist. Using their knowledge of radioactivity and equipment previously part of the Manhattan Project, their team discovered a high concentration of iridium at the Cretaceous-Paleogene boundary in sedimentary layers all over the world, leading them to hypothesise that mass extinction of the non-avian dinosaurs was caused by the impact of a large asteroid. To this day, the Alvarez hypothesis remains the most popular explanation for the gap in the fossil record at around 66 million years ago.

Science is no longer partitioned by rigid walls. The 'subjects' are no longer well-defined and distinct. Instead, they are gradually mixing and producing vibrant new ideas never seen before. A promising future lies ahead of us.

-- old version--

As part of the scientific community, everyone must have heard of the hierarchy commonly mentioned among the pure sciences. “Biology is just applied Chemistry and Chemistry is just applied Physics”. Physics stands at the top, framing the very fundamental laws that govern the workings of the universe in which we reside. In this hierarchy comes Geology and the Earth sciences, which usually is placed along or even below Biology, even mockingly told to be ‘not a true science’. Physics is well portrayed in sci-fi movies and popular culture, attracting many young minds to pursue cool-sounding fields such as Quantum computing or Cosmology. The Earth sciences struggle to gain such attraction and are still noticeably absent from most high school curricula. As someone interested in both Physics and Geology, I was curious to know the reason behind the contrasting perceptions of the two fields. This was when I came across some fascinating anecdotes from history about Physicists clashing with the Geologists and occasionally finding themselves on the wrong side.

In comparison to other sciences, major ideas in geology emerged and were accepted by the scientific community considerably more recently. Orbital motions of planets were known, basic laws of electrodynamics and thermodynamics were established before one of the first estimates of the Earth’s age was put up in the mid 1800s (the debate continued long into the mid 1900s when the currently accepted value was agreed). The electron and proton were known and Einstein had published his paper on Special Relativity by the time Wegener gave the hypothesis of Plate tectonics in 1912 (which was mostly ignored until the 1950s).

A major reason behind this delay in acceptance is due to the fact that most of the concepts ran against creationists and western religious beliefs of the time, especially the age of Earth turning out to be older than what was mentioned in the Bible. Aside from creationists, issues were raised even within the scientific community.. Here began the clash between two giants - Lord Kelvin and Charles Darwin.

Age of the Earth

Charles Lyell’s first book ‘Principles of Geology’ was also his most famous, most influential, and most important one. It was one of the earliest compiled works in the field of Geology, and the idea of Uniformitarianism promoted in the book inspired many. This included Charles Darwin. The slow gradual changes accumulating over a long span of time making life evolve - the roots of this idea are uniformitarian. Seeing the diversity of life on Earth and the amount of time it would have required to evolve such a variety of forms by a gradual process, Darwin was convinced that the Earth was hundreds of millions of years to billions of years old.

Lord Kelvin gave one of the earliest estimates of the Earth’s age. His calculations were based on the laws of Thermodynamics and the best known Physics of his time. In the 1860s, Kelvin showed that the age of the Earth should be around 20 million years – much lower than what Darwin and geologists of the time had said. Kelvin was severely critical about Darwin and Natural selection, calling Darwin’s age estimate to be an unscientific result. Darwin called Kelvin his “sorest trouble.” Darwin passed away in 1882, uncertain about his life's work.

Kelvin wasn’t proven wrong until radioactive isotopes were used to estimate the age of old rocks. Newly gained knowledge showed that Kelvin had missed out on the heat from radioactive sources deep inside the Earth. Later calculations by other physicists got the value of Earth’s age closer to Darwin’s estimate. In the 1940s, geologist Arthur Holmes read and provided his estimate as 3.35 billion years. Here is where the clash shifted from Kelvin to another physics giant - Edwin Hubble.

Age of the Universe

Until the 1920s, it was widely accepted that the Milky Way encompassed the entire universe, and that the nebulae in the sky were clouds within the Milky Way. All that changed when Hubble showed that the Andromeda galaxy lay not within but outside the then accepted boundary of the universe. This was revolutionary and changed our perception of the universe forever, marking the birth of Modern Cosmology.

Though not directly critical of the work of geologists like Kelvin, results of Hubble’s work conflicted with those of Arthur Holmes. The age of the universe was found by measuring galactic redshifts and plotting velocity vs. distance. The slope of this plot is the Hubble constant and its inverse is the age of the universe. This turned out to be 1.8 billion years old - The Earth was older than the universe!

This discrepancy existed for around a decade and debates continued on who was right. Over the years though, the Hubble constant was measured with higher accuracy and the age of the universe was corrected. Measurements from meteorites also provided a more accurate picture of the age of the Earth. The universe and Earth are currently thought to be around 13.8 and 4.5 billion years old, respectively.

The Young Sun paradox

Studying the early atmosphere of the Earth (3.8 billion years ago) using rocks and minerals, it was found that liquid water should have been abundantly present during that time. First pointed out by George Mullen and great astrophysicist Carl Sagan in 1972, according to the well-tested models of stellar evolution and dynamics, the Sun would have been 30% dimmer than what it is today. This means the Earth would not have received sufficient heat to keep the water in liquid form. This is the young sun paradox. The paradox is still unresolved with various theories proposed, from the greenhouse effect to albedo effects.

As we approach the modern era, we can notice change. From a highly critical Lord Kelvin to Carl Sagan, one of the pioneers in the search for life in the cosmos, a beautiful amalgamation of physics, chemistry, biology and the earth sciences coming together. We get to hear more stories, such as that of the father-son duo of Alvarez. Luis Alvarez was a Nobel prize winning physicist who was part of the Manhattan project that built America’s first atomic bomb, while his son was a geologist. Using the knowledge of radioactivity and equipment previously part of the Manhattan project, they studied and ultimately discovered the crater in the Yucatan peninsula in Mexico. The Alvarez hypothesis, which says that the extinction of the non-avian dinosaurs was due to a huge asteroid impact to this day, is the most popular explanation for the gap in the fossil record around 66 million years ago. Science as a whole is no longer divided by rigid boundaries of well-defined subjects but is gradually mixing and combining to produce vibrant new ideas never seen before. A promising future lies ahead.