History of Life on Earth & Mechanisms of Evolution

• Miller and Urey are scientists who conducted a simple experiment, that yielded very helpful findings in answering questions about how life began on Earth.
• Organic Compounds -these are molecules linked with life and developed through reactions between atmospheric processes and the watery area of Earth.
• RNA -the resulting molecule when organic compounds self- assembled into a self-replicating molecule.
• Pre-cells -resulted when self-replicating RNA enclosed itself in a membrane to protect itself from the outside environment.
• Primitive Cells -these are pre-cells with improved function through the process of evolution
•   Modern Cell -as the cells choose to fit itself for survival, it developed into a structure which is familiar to us today, a cell with a DNA genome.
• This modern cell had led to the development of the first classification of life form on Earth: the bacteria or the prokaryotes. After some time, as the oxygen level on Earth increases the next archetype of cells has developed: The Eukaryotes.
• eukaryotes are the two types of cells in which the prokaryotes are simpler, and the eukaryotes are more complex and have more cell organelles
• How old is our earth?

  4.5 billion years
• life on Earth began most probably

  3.5 billion years ago.
• The first line of evidence that gives us the answer to the question when did life begin on Earth is the stromatolites
• Stromatolites - are “living” rock samples that scientists have discovered and dated to age up to 3.5 billion years old. These are rock formations identical to a living mat of microbes. They have layers of microbes and sediments. Scientists found out that the topmost layer used photosynthesis to obtain food and the lower layer uses the top layers by product to survive.
• Panspermia is a theory that postulates that life had come from outside the Earth
• Absolute Dating -obtaining the actual age of the fossils and rock through radiometric dating or the use of the concept of half-life and the radioactive decay of elements.
• Relative Dating -obtaining the relative age of the rocks or samples, it does not tell the actual age but only uses some principles of comparison which are as follows:
• Law of Superposition -states that the youngest rocks are found on top of the layers and the oldest rocks are found on the bottom
• Law of Original Horizontality - sedimentation or layering of the rocks occur horizontally; if tilting, breaking, or folding of rocks or its layer occur, it happened recently after the horizontal layering.
• Law of Cross-Cutting Relationship -if the rocks under investigation have a cut from igneous rock intrusions, then the intrusions or fault breaks are younger than the rock being investigated.
• Continental drift is the slow, incessant movement of Earth’s crustal plates on the hot mantle
• Geologic Time Scale is a representation of the life forms that have lived and dominated the Earth on a specific time scale
• Geologic is the combination of the word geologic and chronologic, which means rock and time, respectively.
• Eon - largest division of the geologic time scale; spans hundreds to thousands of millions of years ago
• Era - division in an Era that span time periods of tens to hundreds of millions of years
• Period - a division of geologic history that spans no more than one hundred million years
• Epoch - the smallest division of the geologic time scale characterized by distinctive organisms.
• The two eons on the Earth’s geologic time scale: the PRECAMBRIAN, and PHANEROZOIC
• Precambrian is when the origin of life existed, it is when the living creatures are as simple as microorganisms such as bacteria from Hadean, Archean, and Proterozoic eras.
• Phanerozoic is the eon of “everything” after the Cambrian Explosion.

   
• The Cambrian period which took place approximately 540 million years ago is the first period under the Phanerozoic eon,
•  Paleozoic era and is well known for the “Cambrian Explosion”
• Cambrian Explosion during this era, life explodes and teamed with all of the body plans for the evolution of animals diversity that will occur in the time span of 40 million years.
• 3 eras during Phanerozoic eon

  paleozoic

  mesozoic

  cenozoic
• Paleozoic, also known as the “age of invertebrates
• Mesozoic also known as the “age of reptiles
• Cenozoic which is also known as the “age of mammals.”
• Devonian period which is the age of fishes,
• Triassic period when the first dinosaur and the first mammal in the form of rodent appear
• Jurassic period which is the “golden age of dinosaur” when the dinosaurs flourish and also when the first birds appear,
• Cretaceous period when the mass extinction and demise of dinosaurs and 25% of marine life marked the end of the Mesozoic era
• Cenozoic era - when the appearance of the first primates and snakes.