Origins of the Earth Our solar system formed 4.5 – 5 bya Earth – a coalescence of rocks ~ 4.5 bya After sufficient size, gravity strong enough to hold gases

Origins of Life Early atmosphere –Methane (CH 3 ) –Carbon dioxide (CO 2 ) –Ammonia (NH 3 ) –Hydrogen (H 2 ) –Nitrogen (N 2 ) –Water vapor (H 2 O) –C, N, H, and O are basic elements of life

Origins of Life Early Earth inhospitable Once begin cooling, condensation Formation of oceans Set stage for first life – about 3.5 bya

How Can We Look Back Billions of Years Principle of Continuity – Any stage of life’s evolution should derive from preexisting states. Signature Principle – Prebiotic processes should be evident in biochemistry of modern life No-free-lunch Principle – all life requires energy to grow

Hypotheses and Testing These three principles + essentials of life allow for generation of testable hypotheses on formation of life Essentials of Life –Described in introductory lecture

Origins of Life No free oxygen in early atmosphere –But doesn’t all life require oxygen? Precursors for life – simple molecules (remember hierarchy of life) Stanley Miller’s Experiments (1950s)

Simple molecules formed amino acids, purines, and pyrimidines Reaction formed simple molecules

Building Blocks of Life Molecules (amino acids, etc.) are not life Building blocks would continue to accumulate Next step would be formation of macromolecules (proteins, polysaccharides, nucleic acids) Formed by polymerization (repeated condensation of monomers – Chapter 3) Key is a lot of building blocks needed

Building Blocks of Life Molecules are not life – prebiotic For life, three other conditions must be met: –Replicators – self-reproducing molecules –Error via mutation –Energy and partial isolation from environment

Isolation from Environment Why? –Eliminate interference with chemical reactions Protobionts –Aggregates of prebiotic molecules that create an isolated internal environment –Produced experimentally in 1920s

Replicator Molecules RNA was probably first Experiments in 1970s and 1980s demonstrated that RNA could use simple molecules to build nucleotides and more complex molecules A replication error could lead to DNA later after living organisms present

First Life A collection of protobionts Contain all the essentials of life Probably a heterotrophic bacteria Feeding on organic molecules Anaerobic

We will continue topics on the orgins of prokaryotic and eukaryotic life later as we move through those groups