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History and Evolution:
By William E. Steinman:
Part 4, Cosmos and Earth:
April 14, 2003:
For background let's take a very brief look at the evolution of
this universe. I don't pretend to understand this, but it is the
most popular theory among modern scientists. At some time, about
ten or more billion years ago, something happened that produced
a very hot expanding fireball. Also out of this historic event
came some things called matter-energy, gravity, electromagnetism,
the strong nuclear force, and the weak nuclear force. Within this
fireball, hydrogen and helium were also formed.
Now, as this fireball expanded it began to cool and gravity began to act on matter. So, some of the dust of this expanding universe formed into whirling clouds of stuff called primeval galaxies. Within these galaxies primeval stars began to form in the same way and the hydrogen and helium began to combine into heavy elements. What we had from those elements was the makings of a nuclear reaction. That, so we are told, is what a star like our sun really is. It is a self contained ongoing nuclear reaction.
Some of these first stars were quite large and they exploded. When they did, a lot of these heavy elements were hurtled into space. These mixed with clouds of interstellar gas and formed into new stars. One star thus formed was our sun out at the edge of one spiral arm of what we call the Milky Way galaxy. That sun was surrounded by a spinning disk of gas and dust made up of heavy elements from old exploding stars.
Some of this dust accumulated to form planets and one such planet was our very own earth. The earth had all the makings of life as we understand it. The big one is water. Earth had enough to make oceans. It also had plenty of carbon to create the carbon based chemistry on which living organisms are based. So, some time very long ago living organism were born in the oceans of earth.
Our scientists put the formation of the earth at about 4.5 billion years ago. That is one very long time ago indeed. This age of the earth has been determined by geologists through a technique called radiometric dating. This is a fascinating science whereby geologists use spectrography to evaluate the presence of certain isotopes within the sample. By this they can very accurately fix the geological age of their sample. Archaeologists use a similar method called carbon-14 dating to determine the age of fossils.
For the classification of events our scientists have divide up all geological time from earth's formation until now. The first of these is what they call Azoic time. This is the time from earth's formation about 4.5 billion years ago until 3.9 billion years ago. At that time there was no atmosphere. The earth did form a crust and oceans began to form, but there were no known life forms.
The Azoic time was followed by what is called Precambrian time. That is a large part of the earth's history from about 3.9 billion years ago until the Paleozoic Era which began about 540 million years ago. One very interesting thing about Precambrian time is that primitive life forms seem to have existed almost from the beginning. Some were discovered to be present more than 3.5 billion years ago. We will probably never know how or why these life forms came about.
Three eras are defined to cover the time from Precambrian time until now. They are the Paleozoic Era from 540 to 245 million years ago, the Mesozoic Era from 245 to 65 million years ago, and the Cenozoic Era from 65 million years ago to now. Eras are divided into periods. Periods are divided into epochs and epochs are divided into ages. This is a whole new vocabulary for most of us. The real purpose of these time divisions is just to keep geologists on the same page as they discuss historic events. For us it is how we determine when certain events occurred. These events mark the progress of earth's evolution.
The beginning period of the Paleozoic Era was the Cambrian from 540 to 505 million years ago. This period was marked by the appearance of animal life, first as soft bodied animals. These were able to ingest food. How these creatures evolved, we do not know. Later in this period we find species with shells and legs. So as early as 505 million years ago we had animals capable of locomotion.
Many other things occurred during the Paleozoic Era. Marine life was the dominant development, but some of these became amphibians. They could live on land or in water. Mountains began to form and primitive forests formed with ferns and coniferous trees. We also got insects including cockroaches. It seems they have dibs because they were here first. Near the end of this era the first reptiles began to appear.
The Mesozoic Era is called the age of reptiles. The periods are the Triassic, Jurassic, and Cretaceous. It is in this era that dinosaurs and other monster like reptilian life forms came forth. They appeared, thrived for a short geological time, then disappeared. These large reptiles were followed by the smaller lizards and snakes. It was also in this era that flowering plants and modern trees began to appear.
Finally we get to our own Cenozoic Era which is divided into two periods, the Tertiary and the Quaternary. This is where it starts to get interesting for us. We call this the age of mammals. Mammals, of course, include people. In the Tertiary Period from 66.4 to 1.4 million years ago. Europe emerged as the oceans withdrew. Also Greenland split away from North America. Most modern plants and birds were present. This is also when most of the mammals of our modern world began to appear.
The Pliocene Epoch of this period, between 5 and 1.8 million years ago, marked the appearance of the Australopithecines or Southern Apes. One theory has it that these animals are the earliest known ancestors of man. There is a great deal of debate about this in the scientific community. All we can say for sure is these creatures had some of the characteristics of man.
The Quaternary period is divided into two epochs called the
Pleistocene epoch from 1.8 million to 10,000 years ago. This is
the time of the so called Ice Age when glaciers advanced over
the earth. A lot of mammals did not adapt and became extinct.
One that did adapt was man. Homo Sapiens emerged in the Pleistocene
epoch.
The final epoch is the one we currently live in. That is the Holocene
or Recent epoch from 10,000 years ago to now. It is when humans
began to form civilizations and all the wars and strife began.
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