Evolution of Life Life’s Timeline

Origin of Life Studies Life was first thought to arise from spontaneous generation – it “appeared.” Studies to disprove this idea began in the 1600’s with Redi (studies to prove maggots came from eggs) Louis Pasteur’s experiment using broth and curve- necked flasks disproved the idea and proved biogenesis = life comes from other life

Origin of Life Studies Miller and Urey conducted a study to prove that organic compounds could be created from early Earth conditions. They placed water vapor, methane, hydrogen and ammonia in an apparatus and simulated lightening with electrical sparks They were able to create amino acids = building blocks of proteins Similar experiments made nucleic acids, carbohydrates and ATP

1st Life Earth formed about 4.5 billion years ago Life began with heterotrophic prokaryotic organisms based on fossil evidence 3.5-4.0 billion year old rocks have been found with prokaryotic fossils 1st type of prokaryotes were likely ancestors of today’s archaea

2 types of prokaryotes Bacteria are much more common today Archaea are ancient prokaryotes that live in extreme environments. Archaea have RNA polymerase more similar to eukaryotes = likely ancestors of eukaryotes. Original ancient prokaryotes likely evolved into the 2 types and archaea then evolved into all other organisms.

The arrival of O2 Modern Earth is 21% oxygen, but ancient Earth had no oxygen (reason why Miller and Urey’s Experiment had no oxygen) Cyanobacteria = photosynthetic eubacteria began to carry out photosynthesis and release oxygen into the oceans. Eventually oxygen was released into air. Oxygen enabled cells to begin using aerobic cellular respiration to create ATP and ultimately led to more complex species. It later helped protect the Earth

Eukaryotes Evolve Eukaryotes evolved around 1.5 billion years ago First eukaryotic cells were larger than bacteria and had internal membranes. May have evolved when a type of small aerobic prokaryote was engulfed by a larger anaerobic prokaryote. This is called endosymbiosis and scientists believe that the engulfed prokaryotes became mitochondria or possibly chloroplasts in autotrophs.

Multicellular Organisms Fossils of multicellular organisms = 630 million year old rocks. (Advantage of multicellular organisms?) Life then took off in the oceans Most current organisms originated during the Cambrian period (550 million to 500 million years ago) Most major animal phyla/groups evolved during this time.

Life moves to Land Change in atmosphere allowed life to move to land. Oxygen gas (O2) added to the atmosphere by photosynthetic cyanobacteria was broken apart by UV rays and created O3 or ozone. Ozone protects us from UV rays

Animals continue to evolve Invertebrates diversify (Examples: sponges, jellyfish, worms, mollusks, arthropods such as insects, spiders and crustaceans) Vertebrates, animals with backbones, then evolved: Fish (advantage?) Amphibians (advantage?) Reptiles and Mammals (around the same time) (advantages?) Birds (advantage?) Humans (advantage?

Other organisms also evolved Protists Fungi Plants Began with simple plants, such as mosses Eventually evolved to include complex flowering plants called angiosperms

Human Evolution Humans evolved around 200,000 years ago in Africa based on fossil evidence Our closest living relative is the chimpanzee Humans shared a common ancestor with chimpanzees and bonobos 5 million years ago. Orangutans and gibbons (other apes) diverged several million years earlier. We share many similarities with other primates including opposable thumbs, 4 sets of teeth, long periods with our mothers Most of our proteins encoded by our DNA is identical to those in a chimpanzee. (98.4 percent genetic similarity)

Human Evolution Humans and chimps do have significant differences despite our similar DNA. Chimps = long hair covers body, skull, teeth, limbs, feet differ, walk on four legs. Earliest primate to walk upright (exhibit bipedalism) evolved 5 million+ years ago and thus diverged from chimpanzee. Lucy Video – Becoming Human

Human Evolution Humans and closest fossil relatives = hominins Difficult to find hominin fossils (fossils must be found in areas that cover by sediment (water) and thus are hard to find) Hominins are different from other primates due to their bipedalism and larger brain size. Modern humans differ from other hominins because we have larger brains, are capable of conceptual thought and transmit material from generation to generation. We also have culture and can mold the environment to our needs – gives us big responsibility