Monday, March 14, 2011

Summary of Japan Earthquake in Terms of Plate Tectonics

In light of the earthquake and tsunami that hit Japan last Friday, I thought I would talk about the geology that helps explains what happened. While I was in graduate school, the theory of plate tectonics was hitting full stride. Many of the geology department’s special seminars at that time were presented by leading figures who were active in flushing out the details of the theory. 

The new theory of plate tectonics replaced the old continental drift theory that never gained widespread acceptance by the geological community. Continental drift recognized how the east coast of North and South America seemed to fit nicely into the west coast of Europe and Africa. However, the theory of continental drift proposed that the continents somehow were able to float or push through oceanic crust. No one knew how this might occur. How do you explain how rock can drift through other solid rock? However, some felt it was a good theory and they felt that eventually the scientists would discover the mechanism by which this could occur. 

During the late 1960s and early 1070s, the results of various studies began to come together in support of a new theory; one in which the continents were not drifting through the Earth’s crust, but that the continents were fixed to crustal plates that drifted over the Earth’s surface. According to plate tectonic theory, the Earth’s crust consists of approximately 30 rigid plates varying typically from about 10 miles thick for oceanic crust to about 120 miles thick for continental crust.

 Figure 1. The Earth’s Major Tectonic Plates (from USGS)

 There are three kinds of relative motion occurring between these tectonic plates - spreading centers (divergent), such as along mid-ocean ridges; transform faulting, where the plates are sliding past each other; and subduction zones (convergent), where one plate is being overridden by another plate. 

Figure 2.  The Three Types of Tectonic Plate Boundaries (from Rapid Uplift).

Some of the early studies that supported the theory of plate tectonic theory showed that new oceanic crust was being formed along oceanic ridges, such as the mid-Atlantic ridge. This was verified by the study of the age of the rock obtained by deep-sea drilling, at various distances from the ridge. The further away from the ridge, the older was the rock. Additional evidence that was being found about the same time dealt with the pattern of paleomagnetism*. On average, about every 200,000 years the Earth’s magnetic field reverses. The pattern of reversals can be seen in magnetic surveys perpendicular to the oceanic ridges. The reversal patterns on both sides of the oceanic ridge match and can be dated from the rocks that were cored and dated. The reversal patterns show the same pattern as the rock ages; the further one proceeds from the ridge the older the rock.

I like the analogy of an egg to describe plate tectonics. Imagine an egg in which the shell has been cracked into a number of pieces that are still attached to the egg.  Spreading centers occur where two of the egg shell fragments are being pulled away from each other. Perhaps you could think of the whites of the egg seeping up between the spreading shell fragments, sticking to the edges and hardening to form new shell. However, if this was the only mechanism, the size of the egg would slowly begin to increase. The size of Earth, however, has not been increasing in size. To negate this, there are other places on the egg where one shell is being overridden by another. This would be analogous to a subduction zone where one of the Earth’s plates is subducting or diving down under a plate that is overriding it. On other parts of the egg, one shell is simply sliding past another shell.

A short video demonstrates plate tectonics and shows the motions of the Earth's plates over the past 200 million years.

Japan is located above a subduction zone. The northern part of Japan is actually located on a part of the North American Plate (figure 1) that is overriding the Pacific Plate. The Pacific Plate is diving down and to the west under Japan. Friction along the plate boundary is not smooth and most of the time the rock on the two plates sticks together. When the forces between the differential motion of the two plates become strong enough, rupture between the two plates occur and the earth moves. This is when an earthquake occurs. In this latest earthquake in Japan the overriding plate is thought have been lifted as much as 30 feet. The uplifting sea floor also lifted the overlying column of ocean water. Gravity then caused the waters to flow westward toward Japan and eastward toward North America. Although this animation was created to show what happened during Sumatra earthquake and tsunami of 2004, the same mechanism caused the devastation that happened in Japan.

* paleomagnetism – Paleomagnetism is the study of the magnetism left in rock by the Earth’s magnetic field when the rock is formed. As molten volcanic rock rises along the mid-ocean ridges, the iron in the rock aligns with the Earth’s magnetic field and is frozen into the rock as it cools and hardens

Other references:
  1.  Rapid Uplift Blog by Suyrat Kher.
  2.  Japan earthquake: The Explainer, Chris Rowan blog.
  3.  Plate Tectonic Animations, Paleomap Project, Christopher R. Scotese.
  4.  Observe animations of processes that occur along plate boundaries, Exploring Earth Visualization, McDougal Littell.

Wednesday, March 9, 2011

A Flood of Biblical Proportions in North America

The Middle East was not alone in having floods of Biblical proportions. Although there was probably no Noah in North America 13,000 years ago, we had several major floods that were probably even greater than that of Noah’s time. In my book, I mention a flood that occurred when an ice dam holding back the waters of Lake Missoula broke.            

 Between about 14,500 and 12,800 years ago, a large lake about the size of modern Lake Ontario and Lake Erie combined formed in northwestern Montana. The lake, Lake Missoula, was created by continental glaciation that had advanced southward cutting off the drainage of the Clark Fork River to the Pacific Ocean. Prior to the ice dam breaking, the water behind the dam is thought to have been about 2,000 feet deep. With that much water, the ice dam began to float resulting in its breaking up. As the dam broke, water rushed out of Lake Missoula and flooded the downstream areas of Idaho, Washington, and Oregon before draining down the Columbia River Valley to the ocean. In less than two days, the lake is thought to have drained. Following the flood, the ice sheet again advanced to the south, once again damming the Clark Fork River. The cycle of damming and catastrophic flooding is thought to have been repeated about 25 and perhaps as many as 89 times. Today giant ripples are still present in the valley floors and the ancient shorelines are visible in the surrounding hillsides. 

See  for more and, in particular, watch the video about the geology of the Lake Missoula area today.

Additional References:

Monday, March 7, 2011

Origins of Religion

I’ve had some criticism of my book from the religious community, specifically from those of the more fundamentalist tradition.  One thing I’ve been accused of is making Christianity and religion, in general, sound silly. That was not at all my intention in writing the book. What I was trying to show was that Christianity was not the originator of many of these myths – creation, the virgin birth, resurrections, the afterlife, etc. All religions have been built on preceding religions. Very little is new or unique. In the book, I explore the earliest origins and how religion could have arose among a prehistoric hunter-gatherer society. To show the similarities to modern religion, I used some poetic license and did such things as borrow from the Iroquois creation legend, modify it, and stretch it over a period of seven days to match the creation story told in the Bible.

The virgin birth is part of a number of religions leading up to Christianity. Christianity adapted this idea into their belief. Christianity also adapted the resurrection story from previous religions, one of which may have been the Egyptian belief at about the same time. The Egyptian religion that preceded Christianity had a god Osiris who was brought back to life by the female god Isis. Isis and Osiris then had a child Horus, the primary god of the Egyptians. It is not hard to imagine Christianity borrowing the resurrection story from the Egyptian religion. Resurrection is also common among the shamans of various indigenous hunter-gatherer societies, and one description of it that I came across is similar to the way I describe the resurrection of the shaman in the book.

Another thing that Christianity borrowed from previous religions was December 25th as the date of Jesus’ birth. The Christian Church several centuries later adopted this date to coincide with Pagan ceremonies, thinking they could thereby more easily convert Pagans to their religion. See Origins of Religion for numerous other parallels between Christianity and other religions.

The origin of religion that I suggest in my book seems the easiest and most practical explanation. I started thinking this way after taking an anthropology class on Comparative Religion while pursuing  my Anthropology degree. To me is seems entirely possible that an early human had a dream that his dead father or another ancestor accompanied the hunting party on an important hunt for mammoth or bison. Indigenous people often believe that everything contains a spirits, and during dreams, that spirit departs the body and takes part in what is being dreamed. When a person dies, that spirit lives on. If the real hunt was successful, why wouldn’t that person hope that that ancestor would be present, in spirit, on additional hunts (kind of like a good luck charm)? That hope may have evolved into a pre-hunt ritual and finally into prayer. Religion may have started with a dream about an ancestor who was very much missed by his people; probably a former well-liked and successful hunter and leader. That ancestor was God.  

Origins of Religion?  -
Origin Of Religion - History of Belief -

Thursday, March 3, 2011

Geologic Time Analogies

Radiometric dating indicates that the Earth is about 4.570 billion years old. Geologists break down this 4.570 billion years time frame into a calendar as shown below. 

 Some people have a hard time getting their arms around this number (4,570,000,000); so today, I thought I would help give you a perspective of how much time 4.570 billion years really is. 

At a recent symposium which I attended, Dr. Kirk Johnson of the Denver Museum of Nature and Science attempted to help us get a grasp of time by telling us a million years was about the time it would take for your fingernails to grow to the length of 18 miles. Further calculations show that if you were alive when our solar system was created, your fingernails would now be 82,260 miles long. That would long enough to circle the Earth more than 3 times.  I bet you didn’t know that!

The analogy for geologic time that I used in my book, Ancestors of Gods, uses the length of one’s arm span as a scale of time. Holding your arms out to your sides; if the tip of your left hand represents when the earth was first formed and the tip of the middle finger on your right hand represents the present, then life first appears on earth about at the bend of your left elbow. From there to about your right bicep, life consisted of single celled organisms, mostly bacteria. At about your right bicep, the first eukaryotes, single celled organisms with nuclei, appear. The first multicellular organisms don’t appear until about two inches above your right wrist. The first fish appear at about your right wrist bone, the first reptiles at the center of your right palm, and the first mammals at the base of your middle finger. The extinction of the dinosaurs occurs near the last joint in your middle finger. If you were to take a nail file and make a light pass over the fingernail on the middle finger of your right hand, you would eliminate modern man’s time on earth; two passes would eliminate the entire history of hominids, man’s entire post-ape-ancestor lineage.

Included below are a few other interesting analogies:
1.    365 days/1 year analogy
For this analogy we assume the Earth was formed on January 1st and the present is midnight on December 31st. The oldest known rocks, 3.9 billion year old metamorphic rocks from Greenland, would date from late February. Oxygen would first appear on Earth on July 25th. Multicellular life with skeletons would appear in late November and the first mammals would appear on December 15th. The Atlantic Ocean would begin to open up, separating North America from Europe, about December 19th and the dinosaurs would die out on 27th.  Homo sapiens would first appear at 11:49PM on December 31st and the birth of Christianity would occur at 11:59PM.

2.    Trips around the Milky Way Galaxy
The Earth has circled the Milky Way Galaxy 18 times since its conception 4.6 billion years ago. About 2/5’s of an orbit ago, the dinosaurs died out. Almost 2 orbits ago, the first fish appeared on Earth. Multicellular life appeared about 4 orbits ago.  (from geologic_time_galactic/)

3.    The toilet roll analogy
For this analogy, you need a class in an auditorium. A student starts at the front of the auditorium at the present time. As the student slowly walks toward the back of the auditorium and back in time, she unrolls the toilet paper. By the time the student gets to the back of the auditorium, she stops to recognize the time the very first dinosaurs begin to appear on Earth. The student has covered about the last 5% of the Earth’s existence. The student continues across the back of the room and heads down another aisle to the front of the auditorium. By the time she gets back to the front of the auditorium, she has only gone back about 10-15% of the way back to the origin of the solar system. There are still quite a few sheets on the roll of toilet paper.

4.    The glass of beer analogy

I think the students probably came up with this analogy after class on a Friday night.

Now it is your turn. Please leave your favorite analogy or make up one of your own in the comments. To help you make one up, I have included below a time line for the various highpoints in the evolution of the Earth.

Years Ago
Origin of the Earth
Oldest Dated Crustal Rocks
Oldest Evidence for Life
First Oxygen Atmosphere/Ozone Layer Forms
Oldest Metazoan Fossils
Oldest Fossil Fish
First Land Plants
That important first step: Amphibians Evolve
Huge Mass Extinction at End of Permian Period / Close of the Paleozoic Era
First Mammals
First Birds
Atlantic Ocean first opens
Angiosperms (Flowering Plants) on the Scene
Adaptive Radiation of Mammals
Dinosaurs Go Extinct
Close of the Mesozoic Era/ Beginning of the Cenozoic Era
New discoveries of Australopithecus afarensis (Lucy) fossils from Ethiopia
Pleistocene Ice Age begins
Light from the Andromeda galaxy seen today left Andromeda
Age of Homo erectus fossils from Ethiopia
Oldest rocks in the Bahamas
Homo sapiens appears in the fossil record
Last ice sheet retreats from northern United States
Grahams Harbor, San Salvador, Bahamas floods due to rising sea level after ice sheets are reduced to modern day volume
Columbus lands in New World


Source: Ritger, S.D. and R.H. Cummins. 1991. Using student-created metaphors to comprehend geologic time. Journal of Geological Education. 9:9-11. - Calculate your own analogy to deep time. – analogy of time scaled to the human life time.