History of Life on Earth BIOLOGY Chpt - 12 History of Life on Earth

The Theory of Spontaneous Generation Before the microscope, it was commonly thought life arose from NON-LIFE - ABIOGENESIS Flies came from rotting meat! Bacteria came from rotting broth! Francesco Redi - disproved flies came from rotting meat! Louis Pasteur disproved bacteria spontaneously arose from broth! BIOGENESIS- Life must arise from Life!!

HOW DID LIFE BEGIN? How did life form how earth? 2-ways to approach this….. Philosophy - Science

The AGE OF THE EARTH………… Earth formed 4.5 billion years ago! The Earth Began as a hot molten ball of lava.. 3.9 billion years ago water vapor began to appear 3.5 billion years ago-life began! From Geology and Archeology

A History in the Rock Oldest rocks - 3.9 billion years old! They provide us with fossils, casts, imprints, and specimens in amber and ice Most fossils occur in sedimentary rock! Relative dating - layers closer to the surface are younger than those found in deeper layers!

Plate Tectonics and. Continental Drift The crust of the earth is floating on magma! As the magma flows, the crust is broken apart and squeezed together! These plates which hold the continents have moved location and thus affected life forms! Where these plates meet cause earthquakes, and volcanic activity!

From Chemistry-Radiometric Dating ... TYPES Carbon 14 –decays to Nitrogen. half-life 5,730 years. Potassium- decays to Argon then to calcium. half-life 1.3 -5.2 billion years Uranium 238 –decays to lead. Dating….half life 704 million years Radioisotopes-an unstable atom (extra neutrons) Radioactive Decay the breakdown into smaller more stable atoms. Half-life is the time needed for 1/2 of the substance to change!

GEOLOGIC TIME SCALE The History of the Earth is divided into Four Eras Precambrian-oldest fossils of cells / water invertebrates Paleozoic -fish and plants appear Mesozoic- age of the Reptiles Cenozoic- Mammals

Mass Extinction….. 5 major mass extinctions A time when suddenly large numbers of species become extinct ! Sudden Geological changes occur.. Asteroids Volcanic eruptions

If Life comes from Life…. Where or How did the first life form arise J.B. Haldane – and- Alexander Oparin - hypothesized life began in the oceans from complex organic molecules! Harold Urey- and Stanley Miller - 1953 set up a test to see if the hypothesis had merit!

The Primordial Soup ! Stanley Miller’s experiment with the help of Harold Urey produced amino acids, sugars, and other organic compounds! Similar processes have produced ATP- energy carrier, and nucleic acids- the building blocks for DNA! BUT- If there was NO OZONE layer this process could not have happened!

The Bubble Model… Louis Lerman – molecules for life formed within bubbles on the surface of the ocean. gases trapped in ocean vents formed bubbles methane and ammonia made amino acids released into atmosphere UV rays forced further molecular change these fell back into the ocean and repeated the cycle.

Proto cells… LIPIDS – (fats) form bubbles in water. COACERVATES- amino acids and sugars form bubbles with cell membrane like structure. MICROSPHERES – amino acid chains form bubbles Scientists Cech and Altman showed that RNA can reproduce itself and can modify its structure over time.

What are these precursors of the first cells?? Scientists disagree about the details of the process that led to the origin of life. Most scientists accept that under certain conditions. The basic molecules of life could have formed spontaneously through simple chemistry.

Simple to Complex Molecules? There is a huge difference between simple and large complex molecules found in living things. How did amino acids link to form proteins? How do nucleotides come together to form long strains of DNA that store the instructions for making proteins?? In the lab, Scientists cannot make proteins nor DNA form spontaneously in water.

But get this…… Scientists have made short chains of RNA, the nucleic acid that helps carry out DNA’s instructions. These RNA molecules have been able to form by themselves in water! Turns out that RNA molecules can act as enzymes to form DNA. Therefore, RNA was the first information storing molecule and it catalyzed the assembly of the first proteins. This molecule changed from generation to generation.

Lipids Lipids tend to gather together in water. (Fats are not water soluble and are hydrophobic.) When some lipids are combined with other molecules, they form tiny droplets with a surface that looks like a cell membrane.

Microspheres Another lab experiment shows that in water, short chains of amino acids can gather into tiny droplets called MICROSPHERES.

Coacervates Another tiny droplet is made out of molecules of different kinds., including linked amino acids and sugars.

What does all this mean? Scientists think that formation of microspheres might have been the first step of creating a cell. One theory says that microspheres fomed, lasted a while, and then dispersed. Over millions of years, some microspheres were able to “survive” because they blended with other molecules and energy. Not living cells though because lacked heredity!

Origin of heredity Even though scientists disagree about the details of the origin of heredity, many agree that double stranded DNA evolved after RNA and that early RNA catalyzed the production of the first proteins. So we still don’t know how life started naturally and spontaneously.

The Evolution of PROKARYOTES The oldest known fossils are the PROKARYOTES. CYANOBACTERIA- blue green algae produced the OXYGEN in air !! Ancient prokaryotes are called ARCHAEBACTRIA.

The first EUKARYOTE CELLS 1.5 Billion years ago… first fossils of Eukaryotes! Eukaryotes have organelles within..(Nucleus and others) Archaebacteria- Cyanobacteria- developed into Chloroplasts and Mitochondria Endosymbiosis occurred.. forming first Eukaryote cell

The ENDOSYMBIOTANT HYPOTHESIS Evidence- Mitochondria –same size as bacteria Chloroplasts and Mitochondria have membranes like bacteria Both have there own DNA Both –have ribosomes like bacteria Both- Reproduce like bacteria Lynn Marguli – Proposed prokaryote cells engulfed smaller cells and formed a symbiotic relationship – of mutualism….. where both benefit!

Multicellularity Protists – Primative unicellular and multicellular organisms Multicellularity Unicellular organisms unite to form multi-cellular organisms Specialization – cells become specialized for a particular function

OZONE LAYER As ozone formed , it allowed life to move onto the land…. First Fungi as it can absorb minerals Plants need the minerals to carry on photosynthesis…they came next.. MYCORRHIZAE- fungi and plants in a symbiotic relationship of Mutualism!

Invertebrates--arrive Arthropods followed plants insects – spiders- centipedes-etc Vertebrates… ..fish were evolving as the arthropods developed on land.. . Amphibians evolved from fish .Reptiles developed the egg .Birds developed from reptiles .Reptiles gave rise to the mammals