Ch. 12 history of life on earth

Most scientists think that the earth was formed from the Big Bang about ~14 billion years ago Radiometric dating has been used to calculate the age of the earth, using radioisotopes that give off radiation A half-life is the amount of time it takes for a chemical to release half of its energy, or to decay Scientists use half-lives to work backwards to calculate age of various objects like rocks and fossils

Primordial Soup Model Hypothesis that the earth’s early ocean contained many different molecules with carbon These organic molecules spontaneously joined in chemical reactions with energy supplied by solar radiation, volcanoes, and ocean vents In 1953, Miller and Urey tested this hypothesis by placing gases they thought were present in early earth’s atmosphere in a glass container and provided an electrical shock A few days later, simple compounds did come together from the carbon, but life was not formed Today, scientists know that the gases used were not present in early earth’s atmosphere

First Cells/Life Bubble model Outer Space Model First Cells/Life Hypothesis that gases from underwater vents and volcanoes rose to the ocean surface and formed molecules that led to life Outer Space Model Hypothesis that bacterial life came on asteroids on earth First Cells/Life Scientists propose that mRNA developed first and made proteins, and that DNA was made from RNA The first cells were prokaryotic cells Prokaryotes Unicellular, no nucleus, no membrane-bound organelles Consists of 2 groups: Eubacteria (bacteria that cause disease) and Archaebacteria (all other prokaryotes)

First Cells/Life Prokaryotes Eukaryotes Scientists think that the first cell was a prokaryote called cyanobacteria, which does photosynthesis Eukaryotes Multicellular, has a nucleus, has membrane-bound organelles Lynn Margulis theorized that the mitochondria and chloroplast organelles used to actually be prokaryote cells, and became engulfed by another cell forming a eukaryotic cells. This is called the endosymbiosis theory Her proof was that those organelles are the same size as prokaryotes, those organelles have their own DNA and ribosomes, and those organelles divide like prokaryotes by binary fission during mitosis Scientists think that the first eukaryotic multicellular organisms were called protests (paramecium) Protests then gave rise to plants, fungi, and animals

First Cells/Life Eukaryotes Multicellularity allows for cell diversity in life processes, which originated in the Cambrian period, 540-505 million years ago In 1909, the Cambrian “explosion” was discovered where almost all modern organisms were preserved in the Cambrian layer, and hardly any fossils are found before this time period in the fossil layer

Life to land Scientists say that life started in the oceans and moved to land when the ozone layer formed in the atmosphere Plants were the first organisms on land where they formed mutualistic relationships Arthropods were the first animals on land They have a hard outer shell, called an exoskeleton, a segmented body, and jointed limbs. Ex: lobsters, insects After arthropods, vertebrates developed, which are animals with a backbone vs. invertebrate without one Fish developed in the sea and amphibians developed from fish To do this, fish had to develop legs, lungs Ex: frogs, salamanders Reptiles evolved from amphibians and had to develop thicker skin, ability to gain heat from the sun, and laying eggs in the soil. Ex: Snake, lizard, turtle

Life to land Birds developed from reptiles, possibly from dinosaur Mammals developed last and are found on land and in the ocean Different populations of organisms are due Pangea