The Origins of Life The Big Bang occurred about 18 billion years ago, creating the universe. The Earth formed about 4.6 billion years ago. Life on Earth probably originated between 3.5 and 4 billion years ago.

Evidence of First life Stromatolites Stromatolites are mounds of banded sediment formed by mobile cyanobacteria. They are found in the warm waters of Australia and off the coast of Baja, Mexico.

Evidence of First Life Stromatolites Stromatolites have been found that date back to 3.5 billion years ago. They are strikingly similar to those produced by modern day bacteria.

Evidence of First Life Fossils Fossilized filamentous bacteria has also been found that dates back to 3.4 billion years. This fossilized prokaryote was found in a 3.4 billion year old stromatolite in Western Australia.

Early Earth When the Earth first formed, it was very different from its current state. It was filled with reducing gases, like H2, NH3, CH4, CO, and CO2. Most notably, the atmosphere of early Earth was completely anaerobic. It lacked a protective ozone layer.

Chemical Origins In the 1920’s, Oparin and Haldane predicted that the conditions of early Earth favored the spontaneous formation of organic compounds. In 1953, Miller and Urey tested this hypothesis.

From Molecules to Cells 1.Small organic monomers formed in reducing atmosphere. 2.Monomers joined to form polymers – binding sites in clay helped concentrate the monomers, while metal ions acted as catalysts. 3.Polymers aggregated to form protobionts. 4.A molecule of heredity originated.

Protobionts Protobionts are aggregates of molecules that have some cell-like qualities such as: –Self-assembly –Response to osmotic forces –Ability to store a membrane potential –Engulfing and splitting

First Life Prokaryotic RNA as genetic material Heterotrophic – absorbed organic molecules from surroundings Anaerobic – oxygen was not present in atmosphere until it was put there by photosynthetic bacteria as a waste product (began accumulating about 2 billion years ago

Origin of photosynthesis Some time after the first living things appeared, cells developed that could perform photosynthesis. These organisms put oxygen into the air as a waste product. About 1.5 billion years ago, oxygen still only made up about 1% of the atmosphere Accumulation of oxygen in the atmosphere is thought to have ended chemical evolution

Open for debate Some scientists believe organic molecules came to Earth from outer space. Meteors have been found containing amino acids and nucleic acids (including several amino acids nonexistent on Earth). There may have been a simpler hereditary molecule that preceded RNA, or maybe RNA was never genetic material. Maybe life began near hydrothermal vents (and still forms there?)

Taxonomy – the classification of living things From that first cell, life has diversified into millions of different forms. These forms are divided into five major kingdoms: Animalia, Plantae, Fungi, Protista, and Monera.