We wish to share with you a sample of our writing for General Biology 2. This is Chapter 3 Evolution and Diversity of Life. Bio 2 is a specialized subject for STEM under K+12.
As usual, the main challenge about writing and developing a topic as large as this is deciding what level of discussion we must aim for. We could not possibly write them all, and even if we must discuss only significant events, even these events are too many. The best approach to take on this challenge is probably to focus on transitions from one stage of history to the next. The geologic time scale is divided into intervals and the marker which separates one from the next had to do with the extinction of species and rise of new ones, emergence of significant land forms, emergence of abiotic factors that destroy one class of organisms but give way to another, chance events such as asteroid impacts, etc.
Hopefully, we can finish this manuscript before August 6, the opening of classes in our school.
History of Life
The history of life and of our planet, in general, is so long when we compare it with length of human life. To count the years our planet had been around is beyond human endurance. Our planet is approximately 4.55 billion years old. If we count integers as fast as the clock ticks in seconds, it would take us 144 years to finish counting 4.55 billion years. That is equivalent to two life times counting from one to 4.55 billion with our fingers.
To see how recent human beings are in geologic time scale, let us do it again by way of analogy. Suppose we compress 4.55 billion years in one day which is equivalent to 24 hours. At what time of the day did the earliest human ancestors (homonid) appear? They appeared at 11:59:22 PM, that is, 38 seconds before midnight. Before this time there were no humans on the planet.
Table 3.1 GENERAL FEATURES OF THE HISTORY OF LIFE
Eons, Eras and Periods
The subdivisions of geologic time scale are not of equal length. The longest time interval is Eons, followed by Eras, and then by Periods. Each period is divided further into Epochs and Ages, but our discussions in this section will go only down to periods. Occasionally, we will mention Epochs and Ages but only when citing events which are truly significant to the history of mammals and to the emergence of Homo sapiens.
Table 3.2 SUBDIVISIONS OF EONS
The first three Eons are grouped together under Precambrian supereon and what follows next is referred to as Cambrian supereon. The two are often simply called Precambrian and Cambrian.
The first describes how it was like to live on Earth when it was barely habitable. It was a inhospitable place for living things to thrive because our planet was exposed to a constant rain of meteor bombs coming from outer space. Its surface was barely solid, it was an ocean of magma. An ocean of hot liquid rock. It was a planet with no or little diversity in life forms. When the rain of meteors and asteroid subsided, prokaryotes appeared and came to be the only life forms to live on Earth for the next 1.5 billion years. In contrast, Cambrian is occupied by a diverse quantity of eukaryotic and multi-cellular life forms. Their diversity and numbers were so dramatic, Cambrian supereon is often described as an explosion of life.
As usual, the main challenge about writing and developing a topic as large as this is deciding what level of discussion we must aim for. We could not possibly write them all, and even if we must discuss only significant events, even these events are too many. The best approach to take on this challenge is probably to focus on transitions from one stage of history to the next. The geologic time scale is divided into intervals and the marker which separates one from the next had to do with the extinction of species and rise of new ones, emergence of significant land forms, emergence of abiotic factors that destroy one class of organisms but give way to another, chance events such as asteroid impacts, etc.
Hopefully, we can finish this manuscript before August 6, the opening of classes in our school.
History of Life
The history of life and of our planet, in general, is so long when we compare it with length of human life. To count the years our planet had been around is beyond human endurance. Our planet is approximately 4.55 billion years old. If we count integers as fast as the clock ticks in seconds, it would take us 144 years to finish counting 4.55 billion years. That is equivalent to two life times counting from one to 4.55 billion with our fingers.
To see how recent human beings are in geologic time scale, let us do it again by way of analogy. Suppose we compress 4.55 billion years in one day which is equivalent to 24 hours. At what time of the day did the earliest human ancestors (homonid) appear? They appeared at 11:59:22 PM, that is, 38 seconds before midnight. Before this time there were no humans on the planet.
Table 3.1 GENERAL FEATURES OF THE HISTORY OF LIFE
Eons, Eras and Periods
The subdivisions of geologic time scale are not of equal length. The longest time interval is Eons, followed by Eras, and then by Periods. Each period is divided further into Epochs and Ages, but our discussions in this section will go only down to periods. Occasionally, we will mention Epochs and Ages but only when citing events which are truly significant to the history of mammals and to the emergence of Homo sapiens.
Table 3.2 SUBDIVISIONS OF EONS
The first three Eons are grouped together under Precambrian supereon and what follows next is referred to as Cambrian supereon. The two are often simply called Precambrian and Cambrian.
The first describes how it was like to live on Earth when it was barely habitable. It was a inhospitable place for living things to thrive because our planet was exposed to a constant rain of meteor bombs coming from outer space. Its surface was barely solid, it was an ocean of magma. An ocean of hot liquid rock. It was a planet with no or little diversity in life forms. When the rain of meteors and asteroid subsided, prokaryotes appeared and came to be the only life forms to live on Earth for the next 1.5 billion years. In contrast, Cambrian is occupied by a diverse quantity of eukaryotic and multi-cellular life forms. Their diversity and numbers were so dramatic, Cambrian supereon is often described as an explosion of life.