Chapter 18- Origin and History of Life

4) Evolution of a Self Replication System

1) RNA Hypothesis- RNA evolved first and so the first cell would have RNA genes. Reverse transcription occurred with RNA and this is how DNA and proteins happened. 2) protein first hypothesis- proteins/polypeptides happened first. The protocol made a plasma membrane and enzymes and eventually made DNA and RNA. 3) polypeptides and RNA happened at the same time- RNA was in the cell an d replicated due to proteins. One of these ways is a way that DNA probably formed. After it formed it would do the regular pathway of RNA to proteins. DNA had to evolve before it could store information.

Life Originated in 4 Stages:

1)Organic Monomers 2)Organic Polymers 3)Protocells 4)Living Cells

1) Evolution of Monomers Hypothesis

1)Primordial Soup Hypothesis 2)Iron-Sulfur World Hypothesis 3)ET Origins Hypothesis

Nutrition

A cell need nutrition from other molecules so it can grow. Protocells were heterotrophic , meaning they consumed organic molecules. May also have carried out chemosynthesis or making organic molecules from inorganic molecules. glycolysis is part of metabolism that breaks chemical bonds to release energy. ATP is a part of this. ALl life on earth uses ATP to fuel cellular metabolism, the way to make ATP must have happened early.

Law of Superposition

A given stratum is considered to be older than the one above it and younger than the one below it.

Protein-First Hypothesis

Amino acids polymerize in the presence of heat. Amino acids collected in puddles along the shore. THen the heat from the sun caused them to form proteinoids, which are small polypeptides that have some catalytic properties. When put in water, proteinoids form microspheres which are structures made of protein and are a lot like cells. The protein first hypothesis assumes protein enzymes arose before the first DNA molecule. The genes that encode proteins followed the evolution of the first polypeptides.

Mass Extinctions

At least 5 mass extinctions have occurred in history. The dinos were thought to have died out from a bolide, which is a large, crater forming projectile that hits earth. We can tell this happened because above the crater there is iridium. Iridium is found in meteors.When it hit the earth there would have been ash and soot in the atmosphere that blocked the sun. Continental drift to the south pole aided in the Ordovician extinction because the land got cold and creatures died. The permian extinction occurred because of too ugh carbon dioxide in the air.

Abiogenesis

Chemical and biological evolution. Th origin of life from nonliving matter.

Coacervate Droplets

Concentrated mixtures of macromolecules that give rise to these complex units. Have a tendency to absorb and incorporate various substances from the solution. A boundary forms around the droplet.

Continental Drift

Continents are not fixed but their positions and the positions of the oceans have changed over time. They were joined together to form a supercontinent called Pangaea. Then they split into 2 continents called Gondwana and Laurasia, and then split into the continents of today. This explains why coastlines are mirror images of each other and look like puzzle pieces.It also explains the unique distribution of several fossils, like the emus ostriches and rheas of SA, Africa and Aust. Each continent has its own similar but unique mammals that evolved after the continents drifted apart. Marsupials also were able to diversify in Aust, without competition from mammals elsewhere. Aided in the Ordovician extinction. the continents went to the south pole. the land got cold and a lot of creatures died.

Geologic Timescale

Divides the history of earth into eras, periods, and epochs.

Sedimentation

Fossils are found in sedimentary rock. the settling of particles of eroded rock and soil called silt carried by water.Silt is deposited and forms layers of particles called sediment. Sediment calls stratum which is a layer of sediment in a sequence. Fossils can also be found in tar, ice, bogs and amber. Shells, bones, leaves and footprints are commonly found.

Index fossils

Fossils in certain stratum that are the same age and help to identify deposits made at the same time all over the world. Used in relative dating methods.

Cambrian Animals

Had seas with invertebrate life. So much life that it became known as the Cambrian explosion. ALl of todays animals can trace their ancestry back to the Cambrian period based on the molecular clock. A molecular clock is based in the idea that mutations in parts of the genome occur at a fixed rate and aren't tied to natural selection. Animals had exoskeletons, which were hard outside skeletons, and fossils are abundant in this period. mainly in the water.

Mesozoic Era

Happened after the Paleozoic Era. Even after the extinction ended this era, plants and animals continued to survive. The Triassic period had some of these creatures and was the first period in this era. There were cycad ferns and so this period is called the age of cycads (also known in the jurassic period). There were reptiles left over from the permian period of the paleozoic. Reptiles can live in dry environments because of their scaly skin and the fact they lay eggs. Int he Jurassic period there were large flying reptiles in the air and marine reptiles with paddle like arms. Dinosaurs were on land. There were also small mammals. Dinosaurs re thought to have been so big because the surface area to volume ration was favorable to retaining heat. They were ectodermic (coldblooded) Some were endothermic (warm-blooded). During the cretaceous period, there were lots of dinosaurs, like the t rex and triceratops. at the end of this period there was a mass extinction. The raptors and t rex were thought to tie rise to birds. Small mammals appeared in this era and were diverse and by the end of the cretaceous the modern ancestors of the mammals had evolved. But most of them went extinct.

Plasma Membrane

Provides a boundary between the inside of the cell and its outside world. Critical to tot he proper regulation and maintenance if cellular activities, so its important. Made up of phospholipids assembled in a bilayer. Made up of fatty acids. Has a tail and a head. In water fatty acids become small spheres called micelles. Micelles have heads that point out and tails that point in. Micelles can merge to form vesicles. They are larger than micelles and are surrounded by a bilayer of fatty acids. It moves molecules from the outside to the inside of the cell.

Plate Tectonics

Reason continents drift. The earths crust is fragmented into plates that float on a low mantle level. The continents and ocean basins are a part of these plates. Seafloor spreading occurs where molten mantle rick rises and material is added to the ocean floor. This causes the continents to move a few centimeters a year. Subduction zones are where the forward edge of the moving plate sinks into the mantle and is destroyed forming ocean trenches near volcanoes or volcano chains. When 2 continents collide it results in mountains. When 2 plates meet and scrape past each other it is called a transform boundary. This is responsible for earthquakes.

1)Organic Monomers

Simple organic molecules, called monomers, evolved from inorganic compounds prior to the existence of cells.

Primordial Soup Hypothesis

The energy sources on early Earth included heat from volcanoes and meteorites, radioactivity from isotopes, powerful electric discharges in lightning, and solar radiation, esp ultraviolet radiation. A variety of amino acids and other organic acids had been produced. Monomers could have been produced from ammonia coming out of ocean vents. Molecules wouldn't have been destroyed from oxygen or decay and would have survived.

3) Evolution of Protocells

The first cell before the true cell. A structure that has an outer membrane. Also called a protobiont.

Multicellularity

The first multicellular organisms practiced sexual reproduction. Many fossils are thought to be of soft bodied invertebrates (don't have a spinal column)that live in mudflats in water.

biomolecules

The molecules of living things and are organic molecules.

Carboniferous period and coal

The process that turned the forest into coal started n the carboniferous period. the weather got cold and dry and the age of amphibians ended. a mass extinction occurred at the end of the permian period, which ended the paleozoic era.

Fossils

The remains and traces of past life or any other direct evidence of past life. Mainly hard parts of creatures like shells, bones, or teeth, since they aren't con sued or destroyed. Can also be trails, footprints or impressions of soft body parts.

Paleontology

The science of discovering and studying the fossil record and from to making decisions about the history of life ancient climates and environments.

ET Origins Hypothesis

There are organic molecules in some meteorites. These organic molecules could have started the chemical origin of life on Earth.

Iron-Sulfur World Hypothesis

Thermal vents at the bottom of the ocean provided elements and conditions to make organic monomers. This is the iron sulfur world hypothesis, and gases were emitted from thermal vents, and then they pass over iron and nickel sulfide minerals, and these act as catalysts that drive the evolution from inorganic to organic molecules.

Potassium-Argon Dating

Used to date rocks that are 100,000 to 4.5 billion years old. USed instead of radiocarbon dating.

Radiocarbon Dating

Uses carbon 14. It will stabilize into Nitrogen 14. This decay occurs at a constant rate. All living things have the same amount of carbon, so the absolute date can be determined by comparing the amount of carbon to a living thing. Accurate for fossils up to 100,000 years old. After that carbon is too low to detect.

Absolute Dating

Way of determining the age of fossils that relies on radiometric techniques to give a date to fossils. Radioactive isotopes from elements in a fossil have a half life, which is the amount of time it takes for half of that isotope to decay into a stable element.

Precambrian time

When life began, a very long period of time. Prokaryotes were the first cells.They are simple and can live in inhospitable environments. the first fossils are those of prokaryotes. Resemble todays cyanobacteria. There were strange boulders called stromatolites in this time period. Oxygen became part of the atmosphere and formed the ozone shield which allowed living things to love on land and not just organic molecules in water.

Paleozoic Era

lasted 300 mil years.It had 3 major mass extinctions. An extinction is the total disappearance of all the members of a species or group. Mass extinctions are the disappearance of a large number of species or groups within a few m.years.

Invasion of Land

life moved out of the ocean and onto land. The firs plants to develop on land were damp algae. plants were nonvascular (no water conducting tissue). Invertebrates such as arthropods (joints and exoskeletons) were adapted to life on land. Insects are also arthropods and came into life in the Carboniferous period. Vertebrates are animals with vertebral columns. Began with the evolution of jawless fish. The Devonian period is when this happened and is called the Age of Fishes. The seas had fishes covered in exo bones. Amphibians also came about and are thin skinned vertebrates that aren't fully adapted to life on land and still live in the water sometimes. The Carboniferous period is called the Age of Amphibians.

Membrane First Hypothesis

the membrane is important because it protected the molecules from their surroundings and made them able to react quickly and efficiently. The first cell had to have a plasma membrane before any of its other parts.

Cenozoic Era

Has two periods, the Tertiary and Quaternary Period. mammals that survived the extinction of the Mesozoic era had adaptive radiation into the habitats left by the dinos. mammals are warm blooded and have hair. they also produce milk for their young from the mammary glands which is where they get their name from. Some mammals after adaptive radiation took to the air. Some went back to the water. Others stayed on land an became herbivores, carnivores or omnivores. Primates appeared in the eocene epoch 55mya. The first ones were small and squirrel like. Some became adapted to living in trees. Ancestral apes were adapted to the open grasslands. They diversified and gave rise to the first hominids, a group which includes humans. The skeletal difference is that humans walk upright. Bipedal. In the tertiary period the climate got colder and in the quaternary period (in the pleistocene epoch) there were ice ages. There were mammalian megafauna- giant mammals. They died out by the end of the pleistocene. Climate change or human hunting may have been the cause.

Eukaryotic Cells Arise in the Precambrian Time

Is a complex cell that needs oxygen and has a nucleus and other organelles. It acquired these organelles gradually. The endosymbiotic theory says that nucleated cells engulfed prokaryotes and then those became organelles. The first eukaryotes were unicellular.

LUCA

Last Universal Common Ancestor. All life on Earth can be traced back to a single ancestor.This ancestor is common to all organisms that live and have lived on Earth since life began. Living things require energy through metabolism, or the chemical reactions that occur within cells. Living things also respond and interact with their environment, self-replicate, and are subject to the forces of natural selection that drive adaptation to the environment. The first living things had all these characteristics.

Liposomes

Lipids organize themselves into double layered bubbles the size of a cell. Liposomes might have been the first boundary for the cell.

The Origin of Life

Not explained by the theory of evolution, but that theory explains how life on earth became diverse after life began. the history of life is seen by macroevolutionary evidence in the fossil record.

RNA First Hypothesis

Only the macromolecule RNA was needed to progress towards formation of the first cell or cells. The first genes could have been RNA. It could have carried out the processes of life commonly associated today with DNA and proteins.

Iron-Sulfur World Hypothesis

Organic molecules will react and amino acids will form peptides when there is iron-nickel sulfides at thermal vents. They attract amino acids and bind them to make proteins.

2)Evolution of Polymers

Organic monomers join to form polymers in the presence of enzymes. 1)Iron-Sulfur World Hypothesis 2)Protein First Hypothesis 3)RNA First Hypothesis

2)Organic Polymers

Organic monomers were joined, or polymerized to form organic polymers (DNA, RNA, proteins)

3) Protocells

Organic polymers became enclosed in a membrane to form the first cell precursors, called protocells

4)Living Cells

Probionts acquired the ability to self replicate as well as other cellular properties.