History of Life on Earth PDF

THE ORIGIN OF LIFE Historical Development of the Origin of Life on Earth The Origin of Life Earth is much older than life. Based on radioactive decay studies of rocks, it was revealed that Earth is around 4.6 billion years old-1 billion years older than the oldest fossils.  The...

THE ORIGIN OF LIFE Historical Development of the Origin of Life on Earth The Origin of Life Earth is much older than life. Based on radioactive decay studies of rocks, it was revealed that Earth is around 4.6 billion years old-1 billion years older than the oldest fossils.  Theories on the Origin of Life on Earth Extraterrestrial Origin Panspermia The hypothesis explains that life The theory presumes that the "seed" originated on another planet of life exists all over the universe and outside the Solar System. can be propagated through space. Divine Creation Origin from Non-living Matter Many people believe that life Scientists believe that life arose was put on Earth by divine on Earth from inanimate matter forces. after Earth had cooled. Early Life Forms The oldest fossils that have been discovered were found in 3.6 billion year-old rocks that were once sediments on the ocean floor. The tiny fossils that were found in these ancient rocks were bacteria.  Bacteria: Believed to be the first life forms on Earth Eubacteria Archaebacteria Most living bacteria, They are found mainly in including those that hostile environments where cause disease and decay. conditions resemble those of early Earth.  01 Cyanobacteria ▪ Today, biologists believed that the oxygen of early Earth's atmosphere was produced by bacteria. ▪ About 3 bya, a group of photosynthetic bacteria known as cyanobacteria, evolved. ▪ As they carried photosynthesis, oxygen gas is released into the oceans.  01 Cyanobacteria ▪ After hundreds of millions of years, when the oceans had soaked up all the oxygen they could hold, the oxygen began to bubble out of the water and into the air. ▪ Over the billions of years that followed, more oxygen was added to the air, eventually leading to the present composition of the atmosphere.  01 Cyanobacteria ▪ Life was only able to move onto land because of change in the atmosphere. ▪ As cyanobacteria added oxygen gas to the atmosphere, large amounts of oxygen began to diffuse into the upper atmosphere, producing ozone. ▪ The radiation levels on Earth's surface went down to a level that allowed life to move onto dry land.  01 Eukaryotes ▪ More complex life forms appeared in the fossil record. ▪ These organisms known as eukaryotes were much larger than prokaryotes, and they contained a central nucleus and a complicated internal structure. ▪ Over the past 1.5 billion years, eukaryotic cells have evolved into organisms that are composed of many cells.  01 Eukaryotes ▪ It is believed that the first single- celled eukaryote evolved around 2 bya and is the ancestor of all plants and animals that exist today. ▪ By about 400 mya, enough ozone had formed in the atmosphere to make Earth's surface a safe place to live in.  01 Mycorrhizae ▪ The first living things to populate the surface of Earth were plants and fungi. ▪ The solution to the challenge of living on dry land was a unique mutualistic partnership between plants and fungi called mycorrhizae. ▪ Plants provide food to the fungi while the fungi provide nutrients obtained from organic matter to the plants. Scorpion, the 01 first terrestrial animal ▪ Fossil records reveal that plants covered the surface of Earth within 80 million years of their initial invasion. ▪ Animals soon followed plants onto land. ▪ The first animals to leave the water were the arthropods. ▪ The first arthropods to live on land were scorpions. THE HISTORY of LIFE ON EARTH The history of the Earth is recorded in its rocks. Ancient life is preserved in its fossils, volcanism in its minerals, and sequence in its beds. The Geologic Time Scale 01 02 03 04 05 The Earth’s history Divisions in the The setting of The Geologic Time Geologic Time Scale boundaries for each is The time scale division is based on compartmentalize Scale is a was developed is determined by worldwide- d to give a sense of hierarchical set of through the study varying events such applicable pieces of order. This order is divisions as extinction, and observation evidence and is what we call as the magnetic pole describing of layers of rock governed by the reversals, start of a Geologic Time geologic time. and relationships. International particular species of Commission on Scale. organisms, etc. Stratigraphy. Divisions of the Geologic Time Scale An epoch is several million An era is hundreds of years long. It is the division of millions of years long. the most recent periods. Eon Era Period Epoch Age Represents the biggest A period is tens of millions of The smallest unit of time division that spans years long. It is based on the geologic time and is hundreds to thousands of forms of life existing at that usually only a few millions of years. time. million years in length.  What was the Earth like millions of years ago?  0.5 bya Rapid diversification of animals; plants 1.0 bya and fungi appear; Major events showing how life origin of humans Earliest animals; originated on Earth since 4.6 first multicellular organisms; diverse billion years ago protists 1.5 bya First ▪ For 2 billion years, bacteria 2.0 bya eukaryotes were the only living things on Diverse and the planet. abundant ▪ In the last 570 million years, bacteria 2.5 bya there has been a rapid Photosynthesis diversification of multicellular begins life. Plants, fungi, and most 3.0 bya major animal groups have Bacteria evolved in this relatively short diversify 3.5 bya period of time. First bacteria appear  0.5 bya Rapid diversification of animals; plants 1.0 bya and fungi appear; Major events showing how life origin of humans Earliest animals; originated on Earth since 4.6 first multicellular organisms; diverse billion years ago protists 1.5 bya First ▪ Scorpions evolved. 2.0 bya eukaryotes ▪ More complex animals began Diverse and to evolve. abundant ▪ For over 100 million years, bacteria 2.5 bya jawless fishes were the only Photosynthesis vertebrates. begins ▪ Eventually, the jawed fishes 3.0 bya evolved approximately 400 Bacteria mya. These are the sharks and diversify 3.5 bya bony fishes known today. First bacteria appear  0.5 bya Rapid diversification of animals; plants 1.0 bya and fungi appear; Major events showing how life origin of humans Earliest animals; originated on Earth since 4.6 first multicellular organisms; diverse billion years ago protists 1.5 bya First ▪ The first vertebrates on land 2.0 bya eukaryotes were the amphibians, which Diverse and evolved from bony fishes abundant about 350 mya. bacteria 2.5 bya ▪ Reptiles evolved from Photosynthesis amphibians about 300 mya. begins ▪ The earliest reptiles gave rise 3.0 bya to a variety of species that Bacteria gradually replaced the diversify 3.5 bya amphibians as the dominant terrestrial animals. First bacteria appear  0.5 bya Rapid diversification of animals; plants 1.0 bya and fungi appear; Major events showing how life origin of humans Earliest animals; originated on Earth since 4.6 first multicellular organisms; diverse billion years ago protists 1.5 bya First ▪ The massive reptiles known as 2.0 bya eukaryotes dinosaurs arose about 220 Diverse and mya. abundant ▪ For more than 150 million bacteria 2.5 bya years, mammals and Photosynthesis dinosaurs coexisted. During begins this time, mammals were 3.0 bya small and did not diversify. Bacteria diversify 3.5 bya First bacteria appear  0.5 bya Rapid diversification of animals; plants 1.0 bya and fungi appear; Major events showing how life origin of humans Earliest animals; originated on Earth since 4.6 first multicellular organisms; diverse billion years ago protists 1.5 bya First ▪ Although most dinosaurs are 2.0 bya eukaryotes now extinct, descendants of Diverse and small insect-eating dinosaurs abundant still exist: the birds. bacteria 2.5 bya ▪ Bird feathers evolved from the Photosynthesis same scales that protected begins the dinosaurs as well. 3.0 bya ▪ Birds, mammals, and Bacteria dinosaurs coexisted until the diversify 3.5 bya sudden extinction of the dinosaurs 65 mya during the First bacteria Cretaceous period. appear  All living things evolved from simple life forms.