Origin of Life Life’s Timeline

1 st Life Earth formed about 4.5 billion years ago Life began with autotrophic bacteria/prokaryotes 3.5 billion year old rocks have been found with bacteria fossils 1 st bacteria were likely ancestors of today’s archaebacteria

2 types of bacteria Eubacteria/true bacteria are much more common today Archaebacteria/ancient bacteria live in extreme environments. Archaebacteria have RNA polymerase more similar to eukaryotes = likely ancestors of eukaryotes. Original ancient bacteria evolved into the 2 types and archaebacteria then evolved into all other organisms.

The arrival of O 2 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. 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 evolved during this time.

Life moves to Land Change in atmosphere allowed life to move to land. Oxygen gas (O 2 ) added to the atmosphere by photosynthetic cyanobacteria was broken apart by UV rays and created O 3 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 Amphibians Reptiles and Mammals (around the same time) Birds Humans

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