Life on Earth During the Precambrian Time Span

Life on Earth During the Precambrian Time Span The Precambrian Time Span is the earliest time period on the Geologic Time Scale. It stretches from the formation of the earth 4.6 billion years ago to around 600 million years ago and encompasses many Eons and Eras leading up to the Cambrian Period in the current Eon. Beginning of Earth The earth was formed about 4.6 billion years ago in a violent explosion of energy and dust according to the rock record from Earth and other planets. For about a billion years, the earth was a barren place of volcanic action and a less than suitable atmosphere for most types of life. It wasnt until about 3.5 billion years ago that it is thought that the first signs of life formed. The Beginning of Life on Earth The exact way life began on Earth during the Precambrian Time is still debated in the scientific community. Some theories that have been posed over the years include the Panspermia Theory, Hydrothermal Vent Theory, and Primordial Soup. It is known, however, there was not much diversity in organism type or complexity during this extremely long period of Earths existence. Most of the life that existed during the Precambrian Time span were prokaryotic single-celled organisms. There is actually a pretty rich history of bacteria and related unicellular organisms within the fossil record. In fact, it is now thought that the first types of unicellular organisms were extremophiles in the Archaean domain. The oldest trace of these that have been found so far is around 3.5 billion years old. These earliest forms of life resembled cyanobacteria. They were photosynthetic blue-green algae that thrived in the extremely hot, carbon dioxide-rich atmosphere. These trace fossils were found on the Western Australia coast. Other, similar fossils have been found all over the world. Their ages span about two billion years. With so many photosynthetic organisms populating the earth, it was only a matter of time before the atmosphere started to accumulate higher levels of oxygen since oxygen gas is a waste product of photosynthesis. Once the atmosphere had more oxygen, many new species evolved that could use oxygen to create energy. More Complexity Appears The first traces of eukaryotic cells showed up about 2.1 billion years ago according to the fossil record. These seem to be single-celled eukaryotic organisms that lacked the complexity we see in most of todays eukaryotes. It took about another billion years before the more complex eukaryotes evolved, probably through endosymbiosis of prokaryotic organisms. The more complex eukaryotic organisms began living in colonies and creating stromatolites. From these colonial structures most likely came multicellular eukaryotic organisms. The first sexually reproducing organism evolved around 1.2 billion years ago. Evolution Speeds Up Towards the end of the Precambrian Time period, much more diversity evolved. The earth was undergoing somewhat rapid climate changes, going from completely frozen over to mild to tropical and back to freezing. The species that were able to adapt to these wild fluctuations in climate survived and flourished. The first protozoa appeared followed closely by worms. Soon after, arthropods, mollusks, and fungi showed up in the fossil record. The end of the Precambrian Time saw much more complex organisms like jellyfish, sponges, and organisms with shells come into existence. The end of the Precambrian Time period came at the beginning of the Cambrian Period of the Phanerozoic Eon and Paleozoic Era. This time of great biological diversity and rapid increase in organism complexity is known as the Cambrian Explosion. The end of the Precambrian Time marked the start of the more quickly progressing evolution of species over Geologic Time.

Breaking Down the Pros and Cons of Grade Retention

Breaking Down the Pros and Cons of Grade Retention Grade retention is a process in which a teacher believes that it would benefit a student to keep them in the same grade for two consecutive years. Retaining a student is not an easy decision and should not be taken lightly. Parents often find the decision agonizing, and it can be difficult for some parents to climb entirely on board. It is necessary to note that any retention decision should be made after much evidence is collected and after several meetings with parents. It is essential that you do not spring it on them at the final parent/teacher conference of the year. If grade retention is a possibility, it should be brought up early in the school year. However, intervention and frequent updates should be the focal point for most of the year. What Are Some Reasons to Retain a Student? There are many reasons that a teacher may feel that retention is necessary for a particular student. The biggest reason is typically the development level of a child. Students enter school at around the same chronological age but with ​varying developmental levels. If a teacher believes that a student is behind developmentally compared to the majority of students in their class, then they may wish to retain the student to give them â€Å"the grace of time† to mature and catch up developmentally. Teachers may also choose to retain a student because they simply struggle academically when compared to students at the same grade level. While this is a traditional reason for retention, it is necessary to note that unless you figure out why the student is struggling, it is likely that the retention will do more harm than good. Another reason teachers often retain a student is due to the student’s lack of motivation to learn. Retention is often ineffective in this case as well. Student behavior can be another reason that a teacher chooses to retain a student. This is especially prevalent in lower grades. Poor behavior is often tied to the developmental level of the child. What Are Some Possible Positive Effects? The biggest positive effect of grade retention is that it provides students who are truly behind developmentally a chance to catch up. Those type of students will begin to thrive once they are developmentally on grade level. Being in the same grade two years in a row can also provide a student with some stability and familiarity, especially when it comes to the teacher and the room. Retention is most beneficial when the child that is retained receives intensive intervention specific to the areas in which they struggle throughout the retention year. What Are Some Possible Negative Effects? There are many adverse effects of retention. One of the biggest negative effects is that students who are retained are more likely to drop out of school eventually. It is also not an exact science. Research says that students are more negatively impacted by grade retention than they are positively affected by it. Grade retention can also have a profound impact on a student’s socialization. This becomes especially true for older students who have been with the same group of students for several years. A student who has been separated from their friends could become depressed and develop poor self-esteem. Students who are retained are likely physically bigger than their classmates because they are a year older. This often causes that child to be self-conscious. Students who are retained sometimes develop serious behavior issues, especially as they age. What Grade(s) Should You Retain a Student? The rule of thumb for retention is the younger, the better. Once students reach fourth grade, it becomes virtually impossible for retention to be a positive thing. There are always exceptions but, overall, retention should be primarily limited to early elementary school. There are so many factors that teachers need to look at in a retention decision. It is not an easy decision. Seek advice from other teachers and look at each student on a case-by-case basis. You could have two students who are remarkably similar developmentally but due to external factors, retention would only be appropriate for one and not the other. What Is the Process for a Student to be Retained? Each school district typically has its own retention policy. Some districts may oppose retention altogether. For districts that do not oppose retention, teachers need to make themselves familiar with their district’s policy. Regardless of that policy, there are several things a teacher needs to do to make the retention process much easier throughout the year. Identify struggling students within the first few weeks of school.Create an individualized intervention plan to meet that students individual learning needs.Meet with the parent within a month of initiating that plan. Be straightforward with them, provide them with strategies to implement at home, and be sure you let them know that retention is a possibility if significant improvements aren’t made over the course of the year.Adapt and change the plan if you are not seeing growth after a few months.Continuously update the parents on their child’s progress.Document everything, including meetings, strategies used, results, etc.If you do decide to retain, then follow all school policies and procedures dealing with retention. Be sure to monitor and comply with dates concerning retention as well. What Are Some Alternatives to Grade Retention? Grade retention is not the best remedy for every struggling student. Sometimes it may be as simple as providing a student with some counseling to get them going in the right direction. Other times it is won’t be that easy. Older students, in particular, need to be given some options when it comes to grade retention. Many schools provide summer school opportunities for students to attend and make improvements in the areas in which they struggle. Another alternative would be to place a ​student on a plan of study. A plan of study puts the ball in the student’s court sort of speak. A plan of study provides students with specific objectives that they must meet over the course of the year. It also provides assistance and increased accountability for the student. Finally, a plan of study details specific consequences for not meeting their specific objectives, including grade retention.