ORIGIN OF LIFE UNIT 5 EVOLUTION

Macroevolution Many centuries ago, explorers had discovered fossils and understood how it revealed information about the past Fossils showed how past organisms were very different from present These fossils demonstrated macroevolution Macroevolution – the pattern of evolution above the species level

The Beginning of Earth Earth was formed from a cloud of dust and rocks that surrounded the sun

The Beginning of Earth Millions of years later, Earth became covered with rock and ice from the collisions of the solar system

The Beginning of Earth These collisions generated lots of heat which vaporized the remaining water on Earth (preventing the formation of seas and lakes) Millions of years later, life was introduced on planet Earth Earth’s atmosphere was covered with very little oxygen, water vapor and compounds released from volcanic eruptions As Earth cooled, the water vapor condensed into oceans and allowed for hydrogen to escape into space

A.I Oparin and J.B.S. Haldane Organic Compounds Hypothesized that Earth’s atmosphere was a reducing environment Believed that organic compounds were formed from simpler molecules through lightning and UV radiation Believed that organic compounds were produced in vents Hydrothermal vents – areas on the sea floor where hot water and minerals are produced (interior of Earth near volcanoes) Alkaline vents – areas on the sea floor that release warm water (more suited for an environment)

Miller-Urey Experiment Showed the origin of organic molecules

The Fossil Record Shows how Earth was a long time ago and how it evolved over time Shows how organisms have changed and become extinct over time Shows how new species arose from previously existing species The fossil record is NOT completely accurate Many organisms might have died at the wrong time or place Many fossils may have been lost and only a few might have been discovered

Determining The Age of a Fossil Radiometric Dating – a method of determining the age of fossils by basing it off the decay of radioactive isotopes A “parent” isotope decays to its “daughter” isotope at a given rate Half-life – the time required for 50% of a parent isotope to decay Example: Carbon-14 (decays fast) = half life of 5,000 years Example: Uranium-238 (decays slowly) = half life of 5 billion years One can determine the age of a fossil in sedimentary rocks through the ages of its surrounding rocks Example – a fossil is located between two volcano rocks (490 – 500 million years old), therefore the fossil is roughly 495 million years old.

Fossils

Geologic Record Geologic Record – a scale describing the timing and relationship of events that have occurred throughout Earth's history. Divided into 4 eons and 3 eras Eons – Hadean, Archean, Proterozoic, Phanerozoic Eras – Paleozoic, Mesozoic and Cenozoic Each era represent a distinct age in the history of earth and life Boundaries between eras represent major extinction events

Protocells May have formed from fluid-filled vesicles with membrane- like structure Exhibited simple reproduction and metabolism and maintained an internal chemical environment In water, lipids and other organic molecules can spontaneously formed vesicles with a lipid bilayer Adding clay can increase the rate of vesicle formation

Origin of Self-Replicating Molecules The first genetic material was probably RNA, not DNA RNA s single-stranded and can form 3D shapes by folding over on itself Because it can form 3D shapes, it can act as an enzyme  ribozymes Ribozymes can catalyze self-replication of RNA

The First Single-Celled Organisms Earliest forms of life on Earth were stromatolites and prokaryotes Prokaryotes – single celled organisms without a nucleus Example – bacteria and cyanobacteria Stromatolites – a mound of layered rocks that form when certain prokaryotes bind thin pieces of sediment together Found in present day marine bays

Photosynthesis and Oxygen Most atmospheric oxygen (O2) is of biological origin (photosynthesis) Prokaryote similar to today’s cyanobacteria were the first photosynthesizers O2 began accumulating in the atmosphere Oxygen revolution  killed off much of the life on Earth because the organisms could not deal with toxic oxygen The organisms that could survive with oxygen began using to get energy  cellular respiration

The First Eukaryotes Eukaryotes were formed hundreds of millions of years ago Eukaryotes – organisms that contains a membrane-bound nucleus Eukaryotes are much more complex than prokaryotes Unlike prokaryotes, eukaryotes contain a cytoskeleton (a feature that allows cells to change their shape) Endosymbiont Theory – a theory that states how mitochondria and plastids were once small prokaryotes that formed within larger cells Endosymbiont – a cell that lives within another cell, the host cell Can occur through undigested prey or internal parasites

Evidence That Supports the Endosymbiont Theory Inner membranes of chloroplasts and mitochondria are similar to plasma membranes of prokaryotes Chloroplasts and mitochondria divide in a process which looks similar to prokaryotic cell division DNA is found in chloroplasts and mitochondria in a single circular chromosome like circular chromosomes found in prokaryotes The ribosomes found in mitochondria and chloroplasts are more similar to prokaryotic ribosomes that eukaryotic ribosomes

The Origin Of Multicellular Organisms The introduction of eukaryotic cells created a diversity in life The first eukaryotes that had appeared were single-celled Years later, single-celled eukaryotes gave rise to multicellular forms Algae Plants Fungi Animals

The Earliest Multicellular Eukaryotes Small, red algae were the oldest eukaryotes Larger eukaryotes started appearing 600 million years later These fossils were referred as “Ediacaran Biota” Ediacaran Biota – soft bodied organisms Before the rise of large and multicellular eukaryotes, Earth was a microbial world

The Cambrian Explosion Before the Cambrian Explosion, all large animals were soft-bodied Showed organisms to be scavengers rather than predators Cambrian Explosion – a brief, period of time in history when the first large, hard-bodied animals had started appearing Showed how animals had characteristics of being predators Claws Sharp spines Heavy body armor

The Colonization of Land There is evidence that cyanobacteria and prokaryotes were the first to cover earth’s damp surfaces Later, larger forms of life (fungi, plants and animals) started appearing The ability to move from water to land required many adaptations Ability to reproduce on land Ability to prevent dehydration Example – Many plants have waterproof coatings of wax on their leaves that help them prevent dehydration

The Colonization of Land Plants and fungi would work together to survive on land Plants used fungi in the absorption of water and minerals from soil Fungi used plants to obtain their nutrients The most common and diverse land animals were arthropods (insects and spiders) and tetrapods (humans) Arthropods were the first animals to colonize land