TheHistoryofLife

1) How evidence of change in organisms is provided by rocks and fossils. 2) Correlation of geologic time scales and biological happenings. 3) Sequential order by which lil’ molecules create cells in biotic factors.
 * __ The History of Life __**
 * __ What thou wilt discover: __**

Many people ask the question,” What was early Earth like?” We are here to answer this question and several other questions concerning the geological history of our planet.

Vocab: Isotope- Atoms of the same element that have different numbers of neutrons. Fossil- Physical evidence of an organism that lived long ago that scientists use to study the past; evidence may appear in rocks, amber, or ice. Plate Tectonics- The geological explanation for the movement of continents over earth’s thick, liquid interior.
 * __ Section I __**

**__ The Early History of This, the Third Rock from the Sun __** Scientists believe that the whole Earth was very hot. Many volcanoes covered the surface of the Earth, spewing gases into the air that helped form Earth’s early atmosphere. Then 4.4 billion years ago, Earth cooled enough to a point in which water in its atmosphere could condense, making way for life on the newly refreshed Earth.

An essential key to decoding the past are **fossils**. The paleontologists, scientists that study ancient life, use the fossils to decode and unravel the past. Fossils form when an organism dies and is buried in mud, sand, or clay. As time passes, these particles compress and harden into sedimentary rock. Scientists need to date the fossils back to when the organism was living so they can properly label and classify the organism. There is a variety of methods that paleontologists use, including Relative Dating and Radiometric Dating. Relative dating is merely observing and classifying based on appearance, location, and the layers of sediments that the fossil is under. Radiometric Dating is when scientists utilize the radioactive **Isotopes** in the rocks to accurately age the fossils and surrounding rocks, but it is limited to a much smaller range than relative dating.
 * __ History in the Rocks __**

**__ A Trip into the Past (Quick of Course) __** The geological timescale has been divided into four large timeslots. They are called the Precambrian, Paleozoic Era, Mesozoic Era, and the Cenozoic Era. This period of time accounts for about 87% of Earth’s history. The Precambrian is when unicellular prokaryotes evolved to multi cellular eukaryotes, which over time diversified and filled the oceans with invertebrates, such as sponges and jellyfishes.
 * Precambrian **

During this era, the population of organisms on the Earth exploded dramatically. Animals with back bones began to appear in the oceans, and four legged reptiles and amphibians began to appear and later flourish. According to fossil record, the end of the Paleozoic marks a 90% decrease in Earth’s marine species and a 70% decrease in Earth’s land species.
 * Paleozoic Era **

Mammals began to appear during the extent of this era. Fossil record indicates that mammals began as very small organisms. This is the era in which dinosaurs and early birds ruled the roost. The end of this period shows the appearance of many new types of mammals and flowering plants. But at the end of this era, a mass extinction took place, which puzzles scientists still today. 2/3 of all the species at the time went into extinction. Several theories have been formed that explain this mass extinction. Other geological events took place during the Mesozoic that affected the existence of certain organisms, including the theory of continental drift and the idea of Pangaea, or the idea of one large land mass that, over time, has broken apart into different continents and islands.
 * Mesozoic Era **

This era began about 65 million years ago and is the era we are currently in. Mammals began to flourish during the early part of this era, including the initial appearance of primates. The modern human species appeared perhaps 200 thousand years ago, this is extremely recent, considering the enormous geological time line of Earth.
 * Cenozoic Era **

**__ Section II __** Vocab: Prokaryotes- unicellular organisms that lack internal membrane-bound structures. Spontaneous generation- mistaken idea that life can arise from nonliving materials. Biogenesis- idea that living organisms come only from other living organisms. Protocell- large, ordered structure, enclosed by a membrane, that carries out some life activities, such as growth and division. Archaebacteria- chemosynthetic prokaryotes that live in harsh environments, such as deep sea vents and hot springs.

**__ The Origin of Life as We Know It __** Life, along with everything else, had to begin somewhere. As time has passed, a myriad of theories has been created regarding life’s origin, and our knowledge of our beginnings has increased.

In the past, the main ideas of our origins and the origins of other organisms were that certain organisms produced different organisms, such as meat making maggots. This is explained as **[|spontaneous generation]**. In 1668 AD, Francesco Redi disproved spontaneous generation. He proved that certain organisms only produce similar organisms. The creation of the microscope provided Redi with the means necessary to disprove this erroneous theory. In the mid-1800s, Louis Pasteur set out to disprove that microorganisms are not produced by air. His experiment led to the theory of [|Biogenesis.]
 * __ The Early Theories of Our Origins __**

Biogenesis has improved in popularity in the last hundred years, but scientists still doubt whether or not it factually explains the origins of life earth. Scientists do however know that in order for life to have appeared, carbon molecules had to have formed. In the 1930s, a Russian scientist by the name Alexander Oparin formed the hypothesis that the early earth life began in the oceans, and then through energy from the sun, lightning and the core of the earth produced the organic molecules that form our atmosphere. Then, the rain brought the molecules down to earth through what is known as primordial soup. In 1953, two American scientists, Stanley Miller and Harold Urey, set out to prove Oparin’s hypothesis to be correct. They mixed gasses and water and put electrons through the substance. After a week they noticed that small organic molecules had formed, thus supporting Oparin’s theory. The formation of complex organic compounds is the next phase in the origins of life. Protocells are formed, ATP and nucleic acids are formed as well.
 * __ Modern Theories __**

Fossil record indicates that the first photosynthetic **[|prokaryotic]** cells appeared about 3.4 billion years ago. The first forms of possible life on earth were possibly prokaryotic forms that had evolved from a **protocell**. These prokaryotes perhaps utilized the molecules from the earth’s oceans to obtain energy. They were possibly anaerobic, meaning they did not require oxygen to survive. Since they took in and consumed food, they could be considered heterotrophic. As food supply dwindled and diminished, the heterotrophic forms became less abundant due to lack of food. At this time, the autotrophic cells (meaning they produced food) could have been the ancestors of present-day **Archaebacteria**. The early autotrophs possibly utilized glucose through chemosynthesis, and then released the inorganic compounds such as sulfur compounds into their environment, thus creating food for themselves and heterotrophs. Prokaryotes could then possibly have evolved so as to utilize photosynthesis and remove oxygen from water. As these photosynthetic organisms increased in population, more oxygen was concentrated in the earth’s atmosphere. Aerobic organisms began at this time to thrive due to the abundance of oxygen. Fossil record indicates that prokaryotic life increased dramatically around 2.8 billion years ago. With more oxygen in the atmosphere, the sun’s rays possibly could have been converted into ozone molecules, thus creating the ozone layer that exists between 16 and 24 kilometers above earth’s surface. The newly formed ozone layer provided the protection from the harmful ultraviolet rays from the sun, thus making way for the evolution of the eukaryotes, or more complex organisms. In the 1960s, Lynn Margulis, an American biologist, formed the endosymbiont theory. This theory states that eukaryotic cells were formed when a prokaryote ingested aerobic bacteria. The aerobes in the bacteria now provided the prokaryote with the energy it needed to survive. Over time, the bacteria turned into mitochondria, thus creating what we know as animal cells. Some of the prokaryotes continued to look for more particles to ingest. They then ingested cyanobacteria which contain photosynthetic pigments. Over time, these cyanobacteria turned into chloroplasts that needed the host to survive, thus creating plant cells. This theory is supported by modern technology and continues to ring through the halls of modern science. DNA evidence from prokaryotic forms and eukaryotic forms shows a similarity that could have been exactly the same when life first began. Some prokaryotes live symbiotically with some eukaryotes, meaning they live happily together.
 * __ The Evolution of Cells __**