KEY CONCEPT The origin of life on Earth remains a puzzle.

Earth was very different billions of years ago. There have been many hypotheses of Earth’s origins. The most widely accepted hypothesis of Earth’s origins is the nebula hypothesis. The solar system was created from a rotating cloud of gas and dust. Computer models and the Hubble telescope support this hypothesis

Earth was molten and hot due to the bombardment of Asteroids, Meteorites, Comets, and radioactive elements. 4 bya, earth cooled to form the crust. 3.8 bya – Earth cooled, and water vapor condensed to form the seas. Looked brown. Contained iron. Earliest sedimentary rock Hydrogen, carbon monoxide, and nitrogen gas were released. Atmosphere was composed of – ammonia, water vapor, Methane, and carbon dioxide This caused the sky to be pinkish-orange and toxic. No free oxygen yet – not until 2 bya.

Several sets of hypotheses propose how life began on Earth. There are two organic molecule hypotheses. Miller-Urey experiment - 1953 electrodes heat source amino acids water “atmosphere” “ocean” meteorite hypothesis

Miller and Urey experiment Simulation of how life could have formed with the right “abiotic stew” and conditions. able to create amino acids and other organic molecules such as nucleic acids in just one week Abiotic stew consisted of: Methane (CH4), ammonia (NH3), Hydrogen (H), and water vapor (H20) Used spark of electricity –lightning Proved that organic molecules (Carbon) could be produced from inorganic molecules.

Meteorite Hypothesis 1969 meteorite hit Murchison, Australia Contained over 90 different amino acids (organic) Proved that amino acids could have been present when Earth formed or arrived when meteorites or asteroids bombarded the Earth.

There are different hypotheses of early cell structure. iron-sulfide bubbles hypothesis Hot iron sulfide rising from the ocean floor combines with cold ocean water to form chimneylike -hydrothermal vents Proposed 4 bya these compartments acted as a cell membrane for the 1st cell

There are different hypotheses of early cell structure. lipid membrane hypothesis Lipid = fat Liposomes- membrane-enclosed spheres which can be spontaneously produced could have lead to a bilayer (double) membrane surrounding organic molecules 1st cell membrane which led to the 1st cell????????

A hypothesis proposes that RNA was the first genetic material A hypothesis proposes that RNA was the first genetic material. (RNA came before DNA) Ribozymes are RNA molecules that catalyze their own replication. DNA needs enzymes to replicate itself.