History of Life

spontaneous generation

spontaneous generation: since at least the time of Aristotle (4th Century BC), people (including scientists) believed that simple living organisms like worms, beetles, frogs, amd salamanders could come from dust, mud, etc., and food left out, quickly “swarmed” with life by spontaneous generation. This was the idea that non- living objects can give rise to living organisms. For example:spontaneous generation 1- Observation: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times.. Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs.. 2- Observation: In many parts of Europe, medieval farmers stored grain in barns with thatched roofs (like Shakespeare’s house). As a roof aged, it starts leaking. This could lead to spoiled or moldy grain, and there were lots of mice around. Conclusion: It was obvious to them that the mice came from the moldy grain. 3- Observation: Since there were no refrigerators, the daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses. Conclusion: Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies.

In ancient times, people believed in spontaneous generation, that is, they believed that life could be generated from nonliving matter. In 1668, Francesco Redi disproved this theory. Back in the day, people believed that rooten meat could turn into maggots because the maggots often appeared in decaying meat. Redi did the experiment shown below, The conclusion from Redi's experiment was that maggots appeared on the meat only if flies were able to enter the jars and lay eggs.

The First Cell Every cells is made up of many smaller parts. There is the nucleus present in most cells, which contains DNA (deoxyribonucleic acid), which stores the blueprint of the cell. There are mitochondria which break down compounds and produce energy. There are many other parts in a cell, each of which has a specific function. These parts of the cell are made up of proteins, which are made up of long strands of amino acids, which are made up of different combinations of the base elements of carbon (C), hydrogen (H), nitrogen (N), and oxygen (O). Of all the possible types of combinations forming amino acids, only 20 are used in proteins. However, these 20 amino acids can form almost infinite numbers of combinations to create an almost infinite number of proteins. the first proteins evolved from non-living matter.

The early atmosphere was too hot for oxygen (O), nitrogen (N), and other elements to exist alone, as they do today. These elements combined to form methane (CH4), ammonia (NH3), water vapor (H2O), hydrogen sulfide (formula), hydrogen molecules (H2), etc. These where all, and thus the early atmosphere was called a 'reducing atmosphere'. Further, as there was no free oxygen to form an ozone (O3) layer to protect the earth from the harsh ultra- violet radiation (UV Rays) from the sun. Also, there where incredibly violent electrical storms, which where more violent than any which occur today.

Oparin hypothesized that organic compounds where formed in the early earth when the high energy provided by UV Rays, and storms, caused different molecules to react, and create new organic compounds, such as Amino Acids DNA, and RNA. Urey and Miller began experimenting to prove Oparin's theory. Miller built an apparatus which circulated gasses likely to be present in the early atmosphere (Methane (CH4), Ammonia (NH3), Water (H2O), and hydrogen (H2) ) past an electrical discharge, simulating the UV Rays and violent electrical storms present in the early atmosphere. Miller found many organic molecules present, the most important of created compounds where amino acids. This, in effect, proved Oparin's theory that organic compounds could have been created in the early atmosphere.

-The amino acids would have then polymerized into proteins. -The first cells were probably much like coacervates. As a group, these bacteria are called heterotrophic anaerobes, means they were creatures which ate some naturally occurring food and did not breathe oxygen. The fossils of some these oldest known forms of life have been found in Australian rocks dating back 3.5 billion years.coacervatesfossils -Reactions would have led to the building of larger, more complex molecules. A pre-cellular life would have began with the formation of nucleic acids. Chemicals made by these nucleic acids would have remained in proximity to the nucleic acids. Eventually the pre-cells would have been enclosed in a lipid-protein membrane, which would have resulted in the first cells.nucleic acids

Biochemically, living systems are different from other chemical systems by three things. 1- The capacity for replication from one generation to another( DNA) 2- The presence of enzymes and other complex molecules essential to the processes needed by living systems. Miller's experiment showed how these could possibly form. 3- A membrane that separates the internal chemicals from the external chemical environment. -Fossil-Fossil evidence supports the origins of life on Earth earlier than 3.5 billion years ago.