Early Earth and The Origin of Life Chapter 26
The Earth cooled, then what happened? ~ 3.9 billion years ago 1st life formed 1st fossils of life discovered prokaryotes
Ancient Bacterium 1st prokaryotes Fossilized bacterium 3.5 bya Some bacteria of today
Two braches of the prokaryotic tree occurred relatively early. • A split ~ 3 billion years ago • Split into the bacteria and archea. Fossilized bacteria found In stromatolites, mats of bacteria
About 2.7 bya oxygen accumulated in the atmosphere • 1st photosynthesizing bacteria that produced oxygen CYANOBACTERIA
Evidence for Oxygen in early atmosphere…Banded iron formations • O2 produced dissolved in sea precipitated as iron oxide.
Large spike in O2 levels Nearly 10 % increase 2.2 bya What happened? • Evolution of 1st eukaryotic organisms were algae that contained organelles called chloroplasts. • Killed many bacteria survivors are found today Obligate anearobes. • Other survivors became specialize and cell respiration was born.
Evolution of multicellular eukaryotes ~ 1.2 bya 1st multiucellular eukaryotes algae
Then an ice age! 750 –570 mya • Confined life to deep sea vents and areas where glacier melt allowed sunlight through the surface of the waters. Called the SNOWBALL EARTH. • Then the thaw and the first major diversification of eukaryotes evolved then the second diversification in the early Cambrian produced the major lineages we know today.
Plants, fungi then animals colonized the land 500 mya Plants evolved adaptations to land Concurrently with fungi that Obtain nutrients from the plants In return the plants get increased water Absorption SYMBIOSIS Then herbavores and their predators
Animal evolution • Herbavores (plant eating) Predators • Arthropods (invertebrates) Vertebrates (amphibians land dwelling reptiles Birds and mammals Humans)
The origins of life • 4 bya Earth’s crust solidified No life • 3.5 bya 1st Prokaryotes seen • That means that somewhere between 4 bya to 3.5 bya life evolved.
What happened in that 500 million years? • It was thought that life could arise from nonliving matter Spontaneous generation • Louis Pasteur’s experiments showed this not to be true…
So biogenesis life only comes from life, made its way into the scientific community. • But it must have been violated at least once right? • Most scientists see a 4 stage model for the evolution of life.
Evolution of life; 4 stage model • Stage 1: Abiotic synthesis: organic chemicals combined to form the first molecules of biology (amino acids and nucleotides) • Stage 2: The joining of these molecules to produce more complex polymers (proteins and nucleic acids) • Stage 3: The development of these molecules to self -replicate. • Stage 4: The packaging of these molecules into protobionts droplets of membranes.
Evidence for stage 1: Abiotic synthesis: organic chemicals combined to form the first molecules of biology (amino acids and nucleotides) • Oparin-Haldane Hypothesis • Conditions of early Earth were favorable for the formation of organic compounds from inorganic precursors. • Cannot replicate in today’s world rich in O2 (from the evolution of plants) • What effect does O2 have on bond formation? • Miller and Urey tested the hypothesis in the lab
Conclusion of experiment • Organic molecules such as amino acids and nucleotides formed. • Just said it was possible to happen this way, not that it did happen this way.
Other possibilities… • Deep Sea vents • Meteorites may have contained some of the essential materials.
Evidence for stage 2: The joining of these molecules to produce more complex polymers (proteins and nucleic acids) • Heat vaporizes water in solutions that contain these organic molecules result dehydration polymerization of simple polypeptides. • Primitive earth had many heat sources for this to occur ex: lava deep sea vents etc.
Stage 3: The development of these molecules to self-replicate. • Which came first, the chicken (enzyme) or the egg (nucleic acid)? • Answer: Both the chicken is part egg, that is RNA has both information storage capabilites and enzymatic activiy (ribozymes). • RNA can be autocatalytic.
Stage 4: The packaging of these molecules into protobionts droplets of membranes. Natural Selection at the molecular level…