History of Life on Earth Mike Yeoman 9 th Grade Biology

Two Opposing Scientific Viewpoints Steady-State Theory: Developed in 1948 to oppose the Big Bang. Also called the Infinite Universe Theory. Has since been disproven. Big Bang Theory: Proposed as early as 1912, it is the theory with the most evidence and best explains the current state of the universe.

Steady-State Theory Alternative to the “Big Bang” Implies there was no beginning and no end of the universe. New matter must constantly be created. (cannot explain quasars and radio galaxies) Requires an “antigravity” force. Cannot explain cosmic background radiation.

Big Bang Theory: Three Pillars Hubble-type expansion of the universe. Includes redshifts that are interpretted as a Doppler shift. Cosmic microwave background radiation left over from the initial expansion. Abundance of simple atoms like Hydrogen and Helium as a result of nucleosynthesis.

Radiometric dating is used to estimate the age of a substance. Half-life is the amount of time it takes for half of the radioisotope to decay.

The Miller-Urey experiment showed that organic compounds. Two major problems: ammonia and methane were probably not present; there was no ozone to protect the molecules from UV radiation.

Precursors of the First Cells The Miller-Urey experiment and Lerman’s Bubble Model show that it’s possible and gave pathways that could have produced amino acids, lipids, and hydrocarbons. RNA can form spontaneously in water. Messenger RNA acts as an informational storage molecule. Hypothesis: RNA was the first self-replicating information-storage molecule and it catalyzed the assembly of the first proteins.

Formation of Cell Membrane Certain lipids, when combined with other molecules, can form a tiny droplet whose surface resembles a cell membrane. Lab experiments show that in water, short chains of amino acids can form tiny droplets called microspheres. Another type of droplet made of linked amino acids and sugars is called a coacervate. Microspheres are first step towards cellular organization. Longer lasting microspheres would have become more common. Microspheres are not true cells unless they have the characteristics of living things, including heredity. Scientists agree that double-stranded DNA probably came from RNA.

Evolution of Cellular Life Scientists study the best evidence of early life, fossils (preserved or mineralized remains). Marine cyanobacteria are photosynthetic bacteria that produced oxygen in the Earth’s oceans. Two types of bacteria evolved from this: eubacteria and archaebacteria Eubacteria are prokaryotes that contain peptidoglycan in their walls. (Common bacteria) Archaebacteria lack peptidoglycan and have unique lipids

Evolution of Eukaryotes The first eukaryotes appeared 1.5 billion years ago. Eukaryotes are much larger than prokaryotes. Almost all eukaryotes have mitochondria. Only plants and protists have chloroplasts. Mitochondria and chloroplasts are the size of prokaryotes and contain their own DNA

Size and Structure Genetic Material Ribosomes Reproduction

Six Kingdoms include: Eubacteria, Archaebacteria, Protists, Fungi, Plants, and Animals. Protists are often times unicellular and nonspecialized. Some are like animals, some carry out photosynthesis. Protists make up about half of the biomass of the Earth.

Burgess Shale shows creatures from “Cambrian Explosion” 505 to 438 mya Mass extinction about 440 mya where a large percentage of species were wiped out. 5 mass extinctions throughout history. Possible current mass extinction.

Life Invaded the Land Ancient cyanobacteria produced oxygen, some of which became ozone. Ozone enabled organisms to live on land. Plants and Fungi formed mycorrhizae and were the first multicellular organisms to live on land. Arthropods were the first animals to leave the ocean.

More Life on Land The first vertebrates to invade dry land were amphibians. The extinction of many reptile species enabled birds and mammals to become the dominant vertebrates on land. The movement of the continents on the surface of the Earth has contributed to the geographic distribution of some species.