Putting Numbers on Geologic Ages

Abstract

While geologists knew simply that the Earth was very old, physicist Lord Kelvin calculated its age to be about 100 million years. On the basis of the rate of delivery of salt to the ocean by rivers, the Earth’s age was calculated to be 90 million years. Many geologists felt that these ages were too short to account for everything that had happened. A major breakthrough came at the end of the nineteenth century with the discovery of radioactive decay of heavy elements. Also, at the end of the century Svante Arrhenius noted that the carbon dioxide being introduced into the atmosphere from burning fossil fuels would warm the planet. It was soon realized that the rates of decay of radioactive elements could be used to date rocks. The Earth’s age turned out to be measured in billions, not millions, of years. By 1920, a numerical age framework similar to the one we have today had been established.

Intermezzo IV. Graduate Study: Four Universities and Two Degrees in Four Years: Part II. The Summer of 1959 : Field Work in Mexico

After my first year of graduate classes at Stanford, I drove off to Mexico via Dallas to visit my father. My mother had passed away from cancer the year before. My first stop in Mexico was Monterey to talk with the geologists at Petroleos Mexicanos office there. They were very helpful in suggesting places where I might find outcrops (exposures) of Late Cretaceous and Early Tertiary rocks that would contain foraminifera. They explained that there was one important site on the banks of the Rio Panuco that was important, but not easy to reach, so they would meet me in Tampico on a certain date with a jeep and we would go there together. Most of the localities I needed to visit were cuts along the roadsides, so I could do those alone.

In the evening we went to an outdoor restaurant where entire goats and even cows were roasting, rotating on giant spits. I had never seen anything like it. I was introduced to a special drink, the “Petrolero” which consisted of roughly equal parts Tequila and Maggi. Maggi is a Swiss flavoring somewhat like Worcestershire Sauce. The drink does indeed look and taste like petroleum.

However, they gave me a tip about working alone in the field. In those days if you left your car alongside the road and were out of sight, it was considered abandoned, and windshield wipers, tires and anything else that could be easily removed from the car might be taken by passing motorists. The way to avoid this was to hire someone to watch the car while you were away. I asked how I could do this if I was out in the middle of nowhere. They told me to start with my sample collecting near the car, and soon someone, usually a little boy, would appear and ask if I needed him to watch the car. “You give him a peso or two, depending on how long you will be gone, and he will watch the car and everything will be perfectly safe”. To my amazement, this worked, over and over again.

Another tip. Never ask if this is the road to so-and-so. In Mexico at that time it was considered very impolite to answer a question with ‘non’ (no). So the answer would always be ‘si’ (yes) even if so-and-so was off in a completely different direction. You always had to ask the question in such a way that the answer could not be yes or no. So you asked questions like “where does this road go” or “what is the name of the next town”. I was already learning Mexican Spanish on the fly.

One obscure place I wanted to get to was a village named ‘El Mulato’. There were supposed to be Cretaceous and Tertiary rocks exposed on a hillside just east of the village. It was shown on the maps, located about 40 km (24 miles) to the east of Ciudad Victoria. However, the map indicated that there was a only a very rough road leading to it. I had no idea how I would get there. I was sure that my 1956Plymouth would not be able to make it. I found a hotel on the Plaza in Ciudad Victoria, and in the evening, as I expected, it filled with people sitting on the benches and watching the boys and girls in their late teens/early twenties circling around the Plaza. The boys would go single file one way, the girl’s single file the other way. This was how they would look each other over. In Mexico at that time, a ‘date’ US-style was unheard of, at least in small towns. I casually struck up a conversation with some men on one of the benches, asking if they had ever heard of a place called El Mulato. It didn’t take much time before I was directed to one of the more prosperous-looking gentlemen. He knew El Mulato well, he had ranch lands near there. I asked how I could get there. He said he needed to go to check on some things there; if I would share the gas costs we could go tomorrow. Early the next morning we started out. The ‘road’ was simply two ruts through the countryside. Before long we came to a river, which we crossed by simply driving through it. The water came up to the floorboards but that didn’t seem to bother my friend at all. I guess the distance by road was about35 or 40 miles, and we reached El Mulato about noon. The ‘village’ consisted of a few grass-walled huts with earthen floors. I saw the hillside just a short distance to the east. I explained to the people who had gathered around that I wanted to go there and collect some rocks. That was fine, but first they wanted to offer me lunch. We were invited into one of the huts. The ‘stove’ was a mound of clay with a depression in the middle, where some coals were burning. A flat piece of metal served as the only cooking utensil. A little goat meat, some frijoles (beans) and tortillas, and it was a great meal. After lunch my new friend/driver went off promising to be back in a couple of hours. I went to collect my rocks accompanied by all the children in the village. Everything worked out fine. The jeep appeared at the appointed time, and about 3 PM we started back. The sky had become cloudy and it started to rain. It soon changed into a downpour. Before long the road turned into slick mud. The ruts trapped the tires, and sometimes we went sliding sideways forward. My friend/driver took it all in stride; he had apparently done this many times before. I have never seen such driving since. Sometimes going forward, sometimes sliding sideways, we made progress until we came to the river which was now a torrent. I thought we were there for the night. My friend got out, looked at the rushing water, and opened a bag on the back of the jeep. It contained a large sheet of canvas. We wrapped the engine in canvas, and drove through the river in water well over the hood and up to our chests. There was enough air trapped inside the canvas that the engine kept going until we were out of the water. We unwrapped the canvas, let the water drain from the jeep, and after a few minutes we were on our way back into Ciudad Victoria again. We arrived about9 PM the trip back had taken twice as long as the trip to El Mulato. He dropped me off at the hotel, and after he left I realized I didn’t know his last name or have his address—he was certainly the best jeep driver in those parts.

Much of my collecting was done between the Sierra Madre Oriental and the Gulf of Mexico coast. I had originally planned to use Tampico as a base of operations, but I soon found out that in the summer it is unbearably hot and humid. Few of the possible accommodations had air conditioning and even fewer had restaurants. I found a motel on the north side of town where there was a room air conditioner that worked part of the time but would go off unexpectedly. I found myself driving back to the edge of the Sierra Madre each day because that is where most of the exposures of the rocks I was seeking were to be found. Then I discovered, just where the mountains meet the plains, a local paradise, Hotel Taninul. Taninul was a huge hacienda with over100 rooms, few of them occupied in the summer. Rates were less than in Tampico, the food was excellent, and it was cool at night, thanks to the air descending from the Sierra. There was a large natural spring which served as a swimming pool, with a bar in the middle where you could sit on submerged stones and sip tequila. This became my base of operations. There was another American guest staying there, Lon Tinkle, Professor of History at the University of Texas. He was a fascinating character, doing research in Mexico on the war with the Texans. His book Thirteen Days to Glory is a classic.

Finally the day approached when I was to meet the geologists from Petroleos Mexicanos in Tampico. I drove back and spent the night in the semi air-conditioned motel. We met the next morning and drove in a small convoy out the northern road from Tampico to Ciudad Mante. After a while we turned off onto a dirt track, which I was able to follow for several miles. When the going got rough, we decided to leave my car, found a boy to watch it, and went on by jeep. It was a trip of about30 miles through jungle-like vegetation on small tracks. After a while we came to a large chain link fence and gate blocking the way. The gate was padlocked. No one around.

My friends from Petroleos Mexicanos called out “Juan, Juan” several times, as loud as they could. Most men in that area are named Juan, so this was to find out if anyone was nearby. No one appeared. Rather than smash the padlock, we dismantled the gate, taking it off the hinges. When we laid it down beside the road we looked back and there were at least10 people watching us. My friends asked why they hadn’t let us know they were there. They said no one was named Juan. We explained that we were from Petroleos Mexicanos, and PM personnel, as officials of the government, were allowed to go anywhere. They told us that the fence enclosed property of an expatriate American who was gone for the summer. We went on our way and eventually reached the Rio Panuco and the place called ‘El Limón’. We found the exposures of rock we were looking for in a small clearing in the tropical vegetation. If you didn’t know where it was, it would be difficult to spot from the air. We spent most of the afternoon collecting samples.

On the way back we put the gate back together again, good as new. Then, as dusk was falling and we were still on dirt tracks, we hit a rock, and the jeep soon came to a halt. One of the Petroleos Mexicanos geologists crawled underneath and found that the rock had torn a hole in the fuel line. I though we were there for at least the night if not several days before someone happened along. But, this was Mexico, and after a few minutes, a boy appeared. Out of the jungle. We explained what we needed. He disappeared, and about15 min later reappeared holding a replacement segment of fuel line. We thanked him and paid him for his trouble and drove on back to my car, where the boy was still dutifully watching it. And then drove back to the highway. There we parted company, the Petroleos Mexicanos geologists headed back to Tampico, and I, with the samples, back to Taninul and several Margaritas.

A few days later I left Taninul and drove to Mexico City in one day. It didn’t look far on the map, but a short distance south of Ciudad Valles the highway starts up the Sierra Madre Oriental toward the Central Plateau. The road became a narrow two-lane highway on high steep mountainsides with spectacular drop-offs. Heavy truck traffic made it slow going. My first view of the Valle de Mexico and its city was from the north in early evening. I should have known, but I really had no idea Mexico City was so large. And it is in a truly spectacular setting, in a valley at7,400 feet with the two great volcanoes, Popocatépetl and Ixtlacihuatl, both about17,000 feet high dominating the skyline to the southeast. I made my way down into the city, and eventually found the Paseo de la Reforma and the hotel just off it where I had reserved a room, the Maria Christina. The next day I called Tom Cranfill and found he was living in an apartment not far away, at Rio Tigris 24. We met, and Tom noted that there were apartments in the same building that could be rented by the week or month, saving me a lot of money. I moved in to my own Mexico City apartment a couple of days later.

What amazed me about Mexico City was that it was a typical European city in almost every way. Streets that didn’t run at right angles, and spectacular architecture spanning almost500  years, and traffic like in Rome. After getting settled in I drove out to the University (UNAM = Universidad Nacional Autonoma de Mexico). It was really easy to get to; down Rio Tigris, across the Paseo de la Reforma, down Genova to the Glorieta Insurgentes, and then straight out Insurgentes Sur until you found the University complex. I knew the UNAM was going to be a spectacular exhibit of modern architecture, but it passed my wildest expectations. I easily found the Geology building, Augustin Ayala’s labs and his assistants and unloaded my samples. They told me they would need a few weeks to process them. That afternoon, after looking around the campus and couple of hours trying to decipher Juan O Gorman’s murals on the library, I drove back into the city center. This time I found myself going round and round in the roundabouts, first at the Glorieta Insurgentes, and then at the even more formidable Angel de la Independencia on the Reforma. I didn’t know the primary driving rule in Mexico City—you are not allowed to hit another car. So if you are trapped on the inside of one of these roundabouts, you just turn and aim across the traffic for the street you want. Other cars will come screeching to a halt fractions of an inch from you. It is considered great sport to scare the wits out of the other driver, but you are not allowed to hit them. Incidentally the same rules seem to apply at the Arc de Triomphe in Paris. Not knowing how the system worked, it took me ten or fifteen minutes to get out of each of the circles and onto finally Rio Tiber and eventually back onto Rio Tigris. I put my car in a garage and swore never to drive in the city again. I had been working with hardly any time off for two years and I was ready for some vacation.

Tom was working on two projects, gathering a series of essays from Mexican authors for a special issue of the Texas Quarterly and purchasing art for the UT art museum. They had a grant for acquisition of art from Mexico, but it had two stipulations—no oil paintings, and nothing costing more than $100. He had a contact, Inés Amor, who ran the Galeria de Arte Mexicano. Inés had been responsible for promoting many well-known artists, and had received the highest award Mexico offers for service to the country—freedom from paying any taxes. A good friend of Tom’s, Hans Beacham, was also living at Tigris 24. Hans was a photographer; he is especially well known for his portraits of Latin American writers and artists. During the summer he would photograph the essayists and artists to be featured in the Texas Quarterly. He was also working on a book on modern architecture in Mexico.

To make matters more interesting during the summer of 1958,the Mexican Presidential elections in were coming up in October. In those days there was no real question who would win the election. The PRI (Partida Institutional Revolucionaria) always won, because the army counted the votes. The PRI candidate was Adolfo Lopez Mateos, and his name was everywhere. The protests against these rigged elections took the form of riots, and these would start in middle August. It was a traditional ritual.

I spent a few days learning my way around the city. There were three forms of public transportation, buses, peseros, and taxis. The buses were crowded but very cheap, the taxis were relativelty expensive, and the peseros were cheap and convenient if you wanted to go where they went. Peseros were cars that would take as many passengers as they could hold. The had specific routes—I used those that went Chapultepec—Paseo de la Reforma—Alameda—Zocalo and back. Another of the major pesero routes was along the whole length of Insurgentes. Between those two routes you could visit almost all the major sights of the city. To get a ride in a pesero you stood on the side of the street and waved your hand and if they had room they would stop and you would squeeze in and hand the driver a peso. The driver would stop and let you out anywhere along the route. The ride was always cozy, usually at least four people on a seat that should accommodate three, but they were fast and efficient, and you could just close your eyes when going through the traffic circles. I’ve often thought we could take a giant leap toward solving public transportation problems in the US if we had peseros.

One of my first visits was to the Hilton Hotel on the Paseo de la Reforma. My father had given me a letter of introduction to the manager along with a note from the manager of the Hilton in Dallas. The purpose was to enable me to cash a check at the Hilton in case I needed to. I had heard that the hotel had been damaged in the earthquake that had hit Mexico City a year earlier. The Reforma Hilton was actually two buildings, an older one that had been a hotel with another name, and a second structure that enclosed it on three sides. The old part of the building was intact and being used. I had heard that the newer part had been damaged so badly it would need to be torn down. But when I arrived in Mexico City the Hilton was still seemingly intact. I went through the bustling lobby on the ground floor of the newer part of the building and figured that the reconstruction must have been completed. I found the manager’s office and introduced myself. We had a chat, he set me up with the cashier so I could cash a check if I needed to (I didn’t), and then he offered to show me something interesting. We went though some back doors and up a rough staircase. We were on top of the lobby. Above us was a totally empty space surrounded by walls about fifteen stories high. All of the structural steel had been removed with the intent that the new hotel would be built inside the old shell, and then the old walls demolished like an unveiling. To me those high, free-standing unsupported walls over the lobby full of people looked like a disaster waiting to happen. After that I never even walked on the sidewalk near the Hilton.

Earthquakes are a fact of life in Mexico City. They caused serious damage in 1957 and 1985. The central part of the city is built on a lake bed. The lake was still there when Hernando Cortes arrived in 1516. The sediments are very soft and filled with water. They have compacted because for many years wells drew out water for the local population. They also compact whenever a heavy weight is placed on then. The big opera house known as the Palacio de Bellas Artes was built of marble and because of its weight has been sinking since completion of its construction in 1934.By 1958it had sunk far enough so that the steps, instead of leading up to it, led down to it. The steps had rotated90°, so that the treads (the flat part of the step) had become the risers (the vertical part of the step) and vice-versa. Another exciting building is the Cathedral on the Zocalo. Built in the 17th century, the high columns along the nave are alarmingly tilted in a variety of directions, but the building has withstood many earthquakes. And then there was the Hotel Bamer, on the Alameda. It had been tilting over the street for years, but the 1957earthquake nudged it a bit further. It was fun to go to brunch on the roof and see that the railings slope downward toward the Avenida Juarez, and to look over the front and see that it was above the center of the sidewalk below. It has survived two subsequent earthquakes.

The sediment underlying the city shakes like jelly when there is an earthquake. There are little earthquakes all the time, and each day I would check the shelves and cupboards to make sure the glassware and dishes were not slowly marching toward the edges. There are some classic sites in Mexico showing the subsidence, and as a geologist I visited as many as I could. One well casing, originally below the ground surface, stood like a monument over 20 feet high.

Tom Cranfill often invited me to go along with Hans and him to visit with artists. Inés Amor had set things up for us, so the 30 artists she had contacted for us knew the rules. Tom already knew from previous experience what was going to happen and suggested we make a pool of funds for purchasing the drawings and etchings we might be offered. Later we could divide them up. Tom said that the younger and even most of the older artists would very anxious to have their works shown in the US and published, and the prices would be very favorable. He was absolutely correct. Our money pool was divided up as to how much we would invest in each artist’s work. I’ve never seen anything like it before or since. Although I was almost totally ignorant on such matters he would ask my opinion and have me help in the selections. We would be looking at the works, and the more pieces we became interested in, the more the prices sank. Finally, after Tom finished his negotiations, he and I would leave with the purchases, and Hans would stay behind to take his portraits.

One evening, over some long gin and tonics, Tom explained his rules for building a personal collection of art. His own personal collection was built around19th century Americans. First, select an age, area, style, and type of media. Unless you are wealthy you had better select contemporary art. The area must be where you live or someplace you regularly visit. The style is a matter of personal taste. The type of media, whether lithograph, drawing, water color, or oil depends to a large extent on the funds available. Next, set an annual budget, whatever you can spare for support of the arts, because you become, in effect, a supporter and driver in the art world. Buy only from reputable galleries or directly from the artists. It is amazing what lurks in the back rooms of galleries and closets of artists. Auctions are OK but only after you know what you are doing (Tom had once picked up some signed Picasso lithographs at an estate sale for a song because no one could read the name). Then he gave me the most important piece of information: spend your entire annual budget on one or at most two items. After40  years you will be amazed at what you were able to accomplish. Then and there I decided to work on building a collection based on contemporary Mexican art purchased mostly from Inés Amor at the Galeria de Arte Mexicana. I was able to do it for a decade, but lost my contacts after Inés passed away. Later, as other contacts developed, I switched to underground art from Communist Czechoslovakia.

I also had the opportunity to look at architecture with a specialist, Hans, who was working on his book Architecture of Mexico: Yesterday and Today, published a decade later. I will only cite one architect, who particularly fascinated me: Felix Candela. Candela invented a new way of building, thin curving sheets of concrete strengthened by internal reinforcing rods. No vertical walls, no flat roofs, just gravity-defying concrete. Some of the structures are breathtaking. To understand Candela’s architecture you have to take a piece of paper, fold it, and then see which areas will bend and which won’t. In the1950s neither mathematical analysis nor computational capabilities were far enough advanced to really understand the forces and stresses involved in his structures. Candela’s architecture challenges all your preconceived notions as to what a building should look like.

By the middle of August things were getting unruly in Mexico City. There had been a tiny increase in bus fares, and some of the students at UNAM decided that this was unfair to the poor. They started hijacking busses, taking them out to the campus and burning them. Soon riding a bus became an uncertain affair, not because you might get hurt, but because you might wind up somewhere other than your destination. It got difficult to catch a pesero or taxi as they took up the slack. Walking became the major mode of transportation. Then, toward the end of the month there was a real riot in the Alameda. Windows along the Avenida Juarez were broken. The police arrested a group of tourists from the US who were standing on the steps of one of the hotels. The reason was obvious; it was a lot easier to arrest the tourists than the rioters. The next day I had an appointment with officials of Petroleos Mexicanos at their building on the Alameda. The sidewalks were still covered with broken glass, and workmen were covering the broken windows with cardboard and plywood. I went to one of the upper floors of the building to meet with senior geologists and thank them for their hospitality. There was not the slightest indication that anything untoward had happened the day before.

Then came a break, an architect friend and his wife from Dallas arrived, and we drove off together to the south, via Puebla, Oaxaca and Taxco. That part of the country south and west of Mexico City is very different from the northeast. It reflects much older cultures, both indigenous and European. Ancient temples and pyramids vie with Baroque and Plateresque (the elaborate Mexican version of Roccoco) architecture. We visited one of the churches in Puebla in which an Aztec altar hides beneath the altar cloth. Then we went on to Oaxaca, visiting the spectacular Mayan ruins at Mitla and Monte Alban. Seeing these through the eyes of a modern architect was a major educational experience. On the31st we went to the Iglesia de la Merced to witness the “Blessing of the Animals”. Everyone brings their animals to the square before and, amidst the ensuing chaos, they receive the blessing of the priest. It is pure impromptu folk theater. In Oaxaca I learned to eat a southern Mexican delicacy, grasshoppers. The market has an extensive section devoted to different kinds of grasshoppers served on a variety of tortillas. Rumor had it that grasshoppers are a significant source of antibiotics; if true, eating them would be a good way to ward off disease.

We returned to Mexico City by way of Taxco. The Thomases had made arrangements for us to stay at the facilities of the Alexander von Humboldt Foundation, a delightful colonial era hacienda not far from the city center. Taxco is a beautiful town and could just as well be in the hills of Spain.

As we drove back into Mexico City it became obvious that the troubles had started. There were no busses on the streets, and we saw groups of people listening to someone giving a speech. After getting back and settled into Tigris 24,I said goodbye to the Thomases as they took off driving back to Texas. Tom and Hans filled me in as to what had been going on in the city. The newspapers gave no indication that anything unusual was going on, but there were incidents of confrontation and violence going on each day. They suggested I collect my samples at UNAM as soon as possible and that we drive together as a convoy back to Texas. Hans, who spoke excellent Spanish, agreed to go with me to the UNAM campus.

We drove out Insurgents Sur but as we approached the University we were stopped at a barricade manned by soldiers. They told us the campus had been taken over by rebellious students and did not want to let us pass. Hans explained that we were American scientists working with the University and needed to pick up some samples that had been left at the Geology Department. Eventually we were allowed to pass through, but told to come back by the same route we went in. On the edge of the campus there was a sandbagged machine gun emplacement and we were stopped again. Again Hans talked us through and again we were warned to come back by the same route. They could see the Geology building, and I expect they watched us through binoculars as we made our trip in. When we arrived at the Geology building we found it to be a mess. It had been all glass on the ground floor, but someone had driven a bus right through the building breaking most of the windows and display cases. There was no one around. We made our way upstairs and very fortunately found the laboratory unlocked. The samples had not been touched since I had brought them in. Gathering them up, we got them downstairs and loaded them into the back of the car. Everything was inspected at the two barricades on the way out. It had become obvious that the situation was far more serious than we had realized in the city center.

We took one more day to pack up our things. Later in the day Mexican friends called Tom to tell him that there were increasing numbers of incidents and advised that we should leave as soon as possible. The next morning we took off, planning to use the ‘central road’ through Queretaro, San Luis Potosi, and Saltillo to the Texas border. We had expected that there might be barricades controlling access to Mexico City. Once out of the city things seemed much more normal. Everything went well for a while; then I noticed a problem with my car. We pulled into Queretaro and I stopped at an auto repair shop. I had too much weight in the trunk, and the rear leaf springs were giving way; another spring needed to be added. They offered to fix the problem in a day. To our sheer amazement, the next afternoon, the car was ready. They had actually made the necessary additional springs themselves from scratch on the spot. In Mexico miracles just happen.

The summer of 1958 was an eye-opening experience for me. I had become familiar with Europe, and to discover that we had a very similar culture south of our border was a revelation. I really had not known that Mexico City and its Aztec antecedent Teotihuacan were always the largest or nearly the largest cities in the world. I was impressed that the racial discrimination that characterized the United States at the time did not exist in Mexico. At that time the Mexican population was estimated to be about10 % European,10 % Indian, and80 % ‘mestizo’ or mixed. And until I spent time in Mexico I had not realized that it was a thriving ‘European-style’ country with major cities on the American continent two centuries before the British colonies achieved any significance.

That fall I worked up my samples, washing the shales to get out the specimens of foraminifera. After spending many weeks picking out specimens and identifying them, I began to put together a picture of what had happened at the end of the Cretaceous in this region. The planktonic foraminifera, those that had lived near the surface of the open ocean showed something quite remarkable. Large specimens (more than  1 mm across) with heavy ornamentation characterized the Late Cretaceous deposits. Then, at what I thought must be the Cretaceous/Tertiary boundary, they were replaced by minute unornamented forms. It was as though something very dramatic had happened to life in the ocean. Hans Thalmann then showed me Russian publications by Martin Glaessner on the same transition in the Caucasus. Everything there was exactly the same as what I had found in Mexico. Whatever had happened, it was a global phenomenon that had wiped out much of the ocean plankton.

The members of the Geology Faculty at Stanford were very conservative. In my thesis defense they smelled the odor of early19th century catastrophism—something they were sure had been thoroughly discredited by more than a century of research. They gave me a hard time for presenting such heretical views. But they couldn’t explain why the same thing should be observed, documented by a highly experienced micropaleontologist, on the other side of the planet. So they let me pass. Immediately following my defense was that of another Ph.D. Candidate, Roger Anderson. He described a very sudden change in the land floras of the Raton Basin in New Mexico, also at the Cretaceous/Tertiary boundary. Many of the same faculty attending my defense was serving on his committee as well. At the party afterward a few faculty suggested that perhaps we were on to something.

Twenty years later Walter and Luis Alvarez presented geochemical evidence that an asteroid had collided with earth at that time, resulting in catastrohic extinction of many life forms.