Post on 01-Apr-2015
History of Life on Earth
Ch. 12
Biology
Ms. Haut
How was the Earth Formed?
According to the BIG BANG, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions.
The Origin of Life Began in Chemistry
• Spontaneous origin—molecules of nonliving matter reacted chemically to form many different simple, organic molecules
Early Earth: Primordial Soup
• Ancient Atmospheric Gases—H2O, CH4 (methane), NH2 (ammonia)
• Additional gases (common emissions of modern volcanoes)—CO, CO2, N2, H2O vapor, H2S/FeS, HCN, H2
• Meteor bombardment
• Lightning, heat, and UV radiation served as energy sources
Can organic compounds be generated under conditions similar to those that existed on primeval earth?
• Stanley Miller and Harold Urey (1950s) designed an experiment that demonstrated the possibility that organic compounds could be generated.
Electrical sparks simulate lightning
Condenser cools gases in a “rain”; compounds collect in an “ocean”
Early atmosphere of gases: methane, ammonia, hydrogen, and water vapor
Found pyrimidines, purines, and amino acids
Organic Chemicals Became Complex
• Many hypothesize that inorganic molecules formed RNA nucleotides
• Short chains of RNA nucleotides may have been the first self-replicating information-storage molecule (acting like enzymes)– Could have also catalyzed the assembly of the
first proteins
First Genetic Material and Enzymes may both have been RNA
Microspheres May Have Led to Cells
• Short chains of amino acids tend to gather into tiny vesicles called microspheres
• Other molecules of different types formed vesicles called coacervates
microsphere Coacervates of lipid
Prokaryotes are the Oldest Organisms
Microfossils
Archaebacteria
• Thought to be closely related to the first bacteria
• Exist in harsh conditions (similar to early Earth)– Extreme heat– Lack of oxygen
Photosynthetic Prokaryotes• Cyanobacteria—among the first to appear • Produced and released oxygen into the oceans• Changed the earth’s atmosphere
Modern stromatolites in Shark Bay, Australia
Mats of photosynthetic organisms – cyanobacteria, algae and phototrophs
Modern Microbialite domes similar to ancient reef structures
First Eukaryotes: Endosymbiosis
• ~1.5 billion years ago• Protists
– Single cells; some cells sharing a symbiotic relationship with others
• Today’s eukaryotes contain mitochondria and chloroplasts
• Because these organelles have their own DNA, they may be descendants of symbiotic, aerobic eubacteria and cyanobacteria
First Multicellular Organisms on Land
• Plants evolved from photosynthetic protists paired up with fungi
Plants could harvest sunlight to make food / fungi could harvest minerals from bare rock
Mycorrhizae
Life Invaded Land
• With the development of photosynthetic bacteria came the development of an atmosphere containing oxygen
• UV radiation from the sun reacted with the oxygen to form the ozone layer around the earth– Protected organisms from destructive radiation,
allowing them to survive on the land
Arthropods
• ~100 million years after plants/fungi covered the earth, animals could survive on land
• Arthropods are believed to be the first– Have hard outer skeleton and
jointed limbs– Lobsters, insects, crabs, spiders
• Specific traits allowed certain animals to survive and reproduce and pass on their genes
Eryon arctiformis
Vertebrates
• Animals with backbones (endoskeletons)
• The first were jawless fishes (500 mya)
• 430 mya jawed fishes
Vertebrates
• Amphibians –first vertebrates on land
• Had lungs, allowing them to absorb oxygen from the air
• Limbs believed to be derived from bones if fish fins
• Strong, flexible internal skeleton allowed animals to be much larger than insects
Plethodon glutinosus: Slimy Salamander
Lysorophid amphibian
Vertebrates
• Reptiles –350 mya • Watertight skin protected
from dessication• Lay eggs with shells on
land• Better adapted to dry
climate
Iguana
Vertebrates
• Birds
• Winged animals
• Can fly
• Hollow skeleton
Evolution of Organisms
• Extinctions –death of a species– opens up niches for other species to become
more abundant
• Continental drift—movement of Earth’s land masses over geologic time– Contributed to geographic distribution of some
species• Marsupials in Australia and South America