ORIGINS OF LIFE NEBULA HYPOTHESIS Most widely accepted

ORIGINS OF LIFE

NEBULA HYPOTHESIS Most widely accepted hypothesis of Earth’s origins States the solar system was formed by a condensing nebula § Nebula – cloud of dust and gas in space

NEBULA HYPOTHESIS Sun formed from nebula Over time material in the nebula pulled together due to gravity Materials that remained in the nebulas disk circled the newly formed sun Repeated collisions of this space debris built up into the planets of our solar system

NEBULA HYPOTHESIS Hadean Eon – first 700 million years of Earth, it was hot and violent Many asteroids and meteorites struck the planet, releasing heat, trapping elements deep in the earth These turned into earths layers and released elements into the atmosphere

ORGANIC MOLECULE HYPOTHESIS Two hypothesis about how life supporting molecules appeared on early Earth. Miller-Urey Experiment Meteorite Hypothesis

MILLER UREY EXPERIMENT Proposed an input of energy from lightning led to the formation of organic molecules from inorganic molecules present in Earth’s atmosphere.

MILLER UREY EXPERIMENT Miller and Urey built a system to test this hypothesis They demonstrated organic molecules could be made by passing an electric current through gas

METEORITE HYPOTHESIS Analysis of a meteorite revealed that organic molecules can be found in space More than 90 amino acids were found on the meteorite, 19 naturally occurring on Earth. Suggests amino acids could have been present when Earth formed, or that these organic molecules arrived on Earth from a meteorite.

EARLY CELL STRUCTURE HYPOTHESIS Two hypotheses about how the first cells may have formed on Earth Iron-sulfide bubbles hypothesis Lipid membrane hypothesis

IRON-SULFIDE BUBBLE HYPOTHESIS Hot iron sulfide mixed with cool ocean water form chimney like structures with many compartments. It is proposed that 4 billion years ago biological molecules combined in these compartments.

IRON-SULFIDE BUBBLE HYPOTHESIS These compartments acted as the first cell membranes, holding the organic molecules in small compartments. From here, cell membranes formed.

LIPID MEMBRANE HYPOTHESIS Proposed that evolution of lipid membrane was a crucial step for the origin of life. Lipid molecules spontaneously formed liposomes (membrane enclosed spheres) Liposomes could then form around organic molecules and act as membranes that separated these molecules from the environment Gave rise to the first cells

RNA AS EARLY GENETIC MATERIAL Hypothesis that states RNA as the genetic material on early Earth

RIBOZYMES RNA molecules that can catalyze specific chemical reactions. Ribozymes catalyze replication and synthesis DNA can’t do this!