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