Origin and Formation of the Earth

The Formation of the Earth

The age of the Earth is a question which is still definitively not answered, but to the best degree of certainty and based on the most reliable dating techniques, Earth is clearly very old. The best estimates for the age of the Earth arrives at a value of 4.5-4.6 billion years. Geologists determine this figure by measuring the radioactive decay of gases trapped in bubbles when melted rock solidifies. The two gases most commonly used to measure age on such a large scale are Potassium and Argon. The Potassium/Argon ratio equals a known normal quantity for these two substances in natural free settings. When rock is molten, gases freely escape. When rocks cool and solidify, the gases of these elements are trapped within small gas bubbles (vesicles). Over time, the ratio of radioactive potassium/argon ratio changes. The rate of this particular radioactive decay is known, and extremely long. By measuring the ratio of these two radioactive elements in pristine gas vesicles which have been carefully opened in lab settings, and then comparing them to normal free ratios, scientists can determine the relative age of the rock. Using this method, scientists have concluded that the oldest rocks on earth are about 3.8 to 4.1 billion years old. There are no rocks older than this anywhere because the earth was being continually re-melted at the surface from the excessive bombardment of loose objects from space. We have a record of this bombardment on the surface of the moon - CRATERS. The Apollo astronauts returned lunar samples, and found the same gases in the rock vesicles, concluding that the moon's surface was 4.4-4.5 billion years old. Since it is widely believed that the Earth formed just prior to the moon, it is reasonable to conclude that the Earth should be 4.5-4.6 billion years old. Volcanic activity and meteoric impacts have melted the original surface rock on a global level such that the oldest remaining rocks are 3.8 to 4.1 billion years old.

Since the cooling and solidifying of the Earth's crust, years of erosion and sedimentation of broken rock fragments have left layers on the original bedrock. By measuring the same decay of radioactive elements in the sedimentary rock, geologists have been able to construct a timeline of Earth's geologic history. With the development of life on the planet, and the deposit of fossils in the rocks, paleontologists have shown that the geologists timeline fits the biologists timeline. The history of the Earth, as best understood by scientific research to date is given below:

The dates and derivations of the various geologic times are given below.

Geologists determined that:
Earth is about 4.6 billion years old
The oldest known fossils are from rocks that were deposited about 3.5 billion years ago
The first abundant shell fossils occur in rocks that are about 570 million years old
The last ice age ended about 10,000 ago

From the geologic record of Earth rock, collected moon rock, and fallen Mars rock, geologists have concluded a possible scenario for the origin of Earth. Keep in mind that much of this information is the result of computer modeling, but outside of a creation event based on one set of data which are not widely accepted by the scientific community, this is the best proposition. While I want to make an effort to give equal representation to differing points of view, it is at present too difficult to include the Creation view here. I suggest you click on their Institute for Creation Research website or go to the Pathlights website and follow the links to the Creation Encylopedia to see how some refute old Earth theories. It will take a great deal of time to work through their extensive reports which conclude that: Earth is young, the geologic record is complete nowhere on Earth, and geologic doctrines on Uniformitarianism and Gradualism are invalid. These two tenants of Geology were put forth by Lyell and Hutton and state that geologic processes that we observe today were happening in the past, and at the same rates. Over time, very small changes happening gradually over time, can produce large scale, observable change. Two quick problems with these doctrines are noted: 1) the rotation of the Earth was significantly faster in the past, the Sun produced significantly less energy, and plate tectonic motions vary depending on their location and effect on Earth's rotation; 2) there are large gaps in the geologic record at every studied location, and there is no continuous fossil record. While I might find some of the ideas of the Creation Institute interesting, I do not appreciate the misuse of the word "Evolution," as so many staunch creationists reference it. Evolution is a biological term which states the gene frequencies of a population change over time. The geologic timeline can be considered a look at the "evolution" of the Earth, but I would prefer to use this word for the subject of the origin and development of life and not to the geologic column. As a trained scientist, I admit that there are plenty of flaws in the theory which is proposed below, and you are once again encouraged to search for the truth yourself and draw your own conclusions based on the evidence which you discover. If you want, you can also check out the Gaia Hypothesis which concludes that the Earth is a living entity.

Here is what can we conjecture about the earliest time of earth's history:

1) A cloud of gas and dust began to collapse and rotate as the sun was forming.

2) Rotation increased in speed as the collapsing cloud got smaller.

3) Faster rotation began to flatten the cloud into a disk.

4) Most of the material was collapsing to the center and became the sun.

5) There was differential separation of original material by weight, with heavier elements gravitating toward the inner parts of the disk, and lighter elements being spun to the outer parts of the disk.

6) This separation left much of the dusty particles in the inner regions and the gases in the outer regions.

7) Small pieces of dust and gas aggregated into 1km-sized objects within the first 10 million years.

8) Once these "seeds" formed, chance collisions made some larger than others, and local gravity caused the larger objects to increase further in size, creating planetessimals.

9) Planetessimals were throughout the disk, before the sun ignited, continually being bombarded by smaller objects, thus increasing the mass of the planetessimal.

10) The larger the planetessimals grew, the greater their gravitational effect became on object in their paths, and the paths were eventually swept clean.

11) When the sun finally ignited, the outflux of solar energy pushed away remaining free gas and dust to the extreme edge of the solar system.

12) The results were inner worlds of rock, outer worlds of gas, and extreme distant objects of ice. Yes, ice! This is possible because water is the most abundant molecule in the galaxy, but its light molecular weight would have caused it to be pushed outward by the outflux of solar energy - creating a great sphere of cometary bodies.

13) Moons formed around certain planets in a series of steps similar to the origin of the solar system, but typically after the major planets formed. The existence of many moons around larger planets is explained by their larger gravitational influence. Scientists believe that many moons of the gas planets in general, were captured objects which were caught in the planet's gravitational well.

14) In this manner, earth was formed ... an object consisting of rock, liquids, and gases.

15) The Iron Catastrophe organized the Earth materials into the internal structure we observe today.

There are two websites I would like you to browse through to get an understanding of the how paleontologists mark time in Earth's history. While I do not wish you to memorize the Eras, Periods, and Epochs, (although such knowledge would greatly impress your friends during an evening get-together) I would like you to be familiar with the idea that Earth's history is one of regular change, demonstrated in the types of sedimentary rock formations and in the fossil lifeforms found there.

Evidence Used By Scientists to Determine the Age of the Earth and Sequence of Ages in the Rocks

During the middle 1800s, Charles Lyell (seen in the image to your left) was presiding over the British Museum of Natural History. A top geologist named Thomas Hutton was making wonderful discoveries of interesting fossils embedded in the rocks, and looking at sedimentation patterns of those same rocks. Lyell was convinced that the Earth was very old, far older than traditional methods of Biblical patriarch and Israelite king lists led religious leaders of the day to estimate a value a little over 6000 years. Lyell noticed the aging patterns of rocks and concluded that much time is required to transform pristine rock into aged rock that was observed. Sedimentary rock could not have developed in a few thousand years. It must have taken millions of years or even longer. Key to Lyell's interpretation was a pair of doctrines:





1) Sedimentary rock is caused by rock formations that are weathered, broken, and washed away and laid down like the sand on a beach or the silt at the bottom of a lake or river. These particles are then cemented together into layers. Such layers will always lie on a horizontal plane and older sediments will subsequently be covered by younger sediments. This think had been present since the late 1600s.

2) The doctrine of gradualism stated that geologic processes happen a slow rates, and that over long periods of time, gradual changes can accumulate into large-scale change. A fine example for USA students is the Grand Canyon. The Colorado River has been running through the Arizona desert for a very long time, and slowly that river has gouged out a canyon in the relatively weak sandstone and limestone of the area. Over a very long time, the gradual process of gouging resulted in the deep canyons observed today.

3) The doctrine of uniformitarianism states that the rate of geologic processes in the past is the same as the rate observed in the present. By thus measuring the present rate of a geologic process and the accumulation of the results of this process, it becomes possible to determine the total time that passed in the development of the final appearance.

What was important for geologists was the determination of age of the igneous rock and the sedimentary rocks with their embedded fossil records. To learn about the techniques that are used to date rocks, please go now to Dating the Rocks.

To learn more, check out Geologic Time at the USGS or at UCMP-Berkeley

The Beginning of Life

There is widespread speculation about the origin of life, and this subject is best suited for AP Biology (a wonderful course offered at Hopkins and taught by an equally wonderful teacher). However, most of you will not be excited about the extreme challenge of AP Biology, and therefore may not be exposed to the truths regarding the origin of life. First, there is no certainty regarding any of the life origin theories. All are theories, which means only that scientific tests have demonstrated a strong connection between hypothesis and experiment. Second, there are many students and teachers of Astronomy who hold to the existence of a divine Creator who made all things. Some believe the Creator made everything in 6 literal days. Some believe the Creator made everything in six literal days separated by huge gaps in time. Some believe the Creator made everything in 6 creative events whose lengths varied and were of great length of time. Some believe the Creator initiated the seeds of life and controlled the course of Evolution. Some believe the Creator made everything, but did so in an unspecified manner and now stands aloof from all. Some do not believe in any form of Creator and hold instead to a belief that all of life originated from random events, proceeding along pathways within the boundaries of natural law. At no point in this course do I wish to support or refute any religious point of view ... this is your business. The Bible defines "faith is the assurance of things hoped for, the conviction of things not seen." Any religion of faith entails a belief and acceptance without submission to a test within the constrains of the scientific method. Furthermore, the existence of a Creator cannot be proven false. A rule of the scientific method is the experiment whose results can be repeated. If enough tests yield the same result, the hypothesis becomes a theory. If the test results always yield the same result, the theory may be designated a law. A "law" is something that happens every time and everywhere. If the test ever yields a result different from the others, it is no longer called a theory and a new hypothesis must be developed. Since the existence of a Creator cannot possible be proved false, it falls outside of a science test. You either believe in a Creator or you do not. You are encouraged to seek answers to your questions about life, the Universe, and everything, and if you hold strongly to any particular religion, I encourage you to challenge your beliefs and convictions. If you hold firm, good for you. If you change your mind, good for you. Either way, you will have exercised your mind to think, and this I believe is healthy. Since this is a science course, we will not attempt to put God to the test, but instead look at the information that Earth and Space offers to us, and try to interpret this information in such a way that a scientifically testable theory can be derived.

As of the date of printing of this page, astronomers have found no evidence of life being anywhere else in the Universe except here. SETI has devoted radio telescope time and even recruited home computer users in their search for extraterrestrial intelligence. Their search has still proven empty. No signals have reached out planet. While many Americans claim to have seen alien spacecraft or even share stories of abductions, none have been accepted by the scientific or journalistic societies. If we are the only place where life exists, how did it begin? If the Law of Biology states "Life only from life," than how can that law be broken initially, but never after? If the surface of Earth was molten in its early stages, where would the oceans come from that became the primordial soup? There are many different life origin theories: Cold Earth, Hot Dry Earth, Hot Wet Earth, and Deep Crust environments suitable for the combination of factors leading to the simplest bacterial cell.

Of interest here in this course is the theory that distant comets may have brought some of the necessary molecules for life's beginnings to the primordial ocean. The comets may have rained down in such large quantities as to give rise to an ocean. Additionally, some hold to a theory called "Panspermia," that state life arose elsewhere, under more stable conditions, and was somehow carried to Earth embedded in some space debris.

Currently, the most highly touted theory for the first lifeform is a high-heat-loving bacteria (Thermophile) which thrived in the deep, moist fissures of the crust, close to the hot mantle. Scientists are enthralled by these bacteria, some of whose relatives may be occupying the hot springs of Yellowstone. To learn more about the origin or life, take my Biology course. For now, I encourage you to appreciate the fact that we exist, and are endeavoring to understand the Universe.

Life may have begun over 3.8 billion years ago, almost immediately after the sterilizing meteoric bombardment ended, but it has struggled ever since against repeated attempts by natural causes to obliterate all traces of it. Whether these natural causes are comet or asteroid impacts, mass volcanism, changes in solar output, gamma ray bursts, or other, paleontologists have found repeated moments of mass extinctions where huge percentages of all of Earth's species of lifeforms are suddenly absent in the fossil record. The extinction webpage offers a view of these events and you can be certain that we face a danger of huge impacts everyday. The Hollywood hype of "Deep Impact," and "Armageddon" fascinated the American public, but much more real was the impact on Jupiter by Comet SL-9 in 1993. The dinosaurs may have been wiped out by a large asteroid impact which struck the Mexican coast 65 million years ago, and who knows when the next killer will come hurtling toward us. All our worrying about meteoric impacts may be moot concerning man unless we succeed in being better stewards of this planet. For now, just remember that Earth continues to be bombarded by meteors every minute, and it is just a matter of time before the next big one hits. You will learn more about this when you study asteroids.





To get a nice perspective on time, please move to Time Scale Model or back to Earth Introduction.

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