HISTORY OF LIFEHISTORY OF LIFE

Chapter 14Chapter 14

How old is the Earth?

What changes have occurred?

What is a Mass Extinction?

How do we know they happened?

Field Museum TripField Museum Trip• Important Questions

• 2,4,9,16,21,24,27,32,43,52,59

The Record of Life The Record of Life

Ch. 14, Sec 1Ch. 14, Sec 1

Early History of EarthEarly History of Earth

• 5 billion years ago our solar system was formed as a swirling mass of gas and dust

• Gravity pulled this material together to form the sun

• Remaining gas and debris circled the newly formed sun

• Collisions between the space debris created the planets

• Earth formed about 4.6 billion years ago, dated by studying the layers of rock that make up the planet

• Young Earth was hot, there was no atmosphere to block UV rays from the sun

• No oxygen to breath• A lot of carbon dioxide

and water

• Life originated in Earth’s oceans 3.9-3.4 billion years ago

• Early life forms would have been very similar to bacteria

History in RocksHistory in Rocks• Rocks provide information about Earth’s history

including the history of life on Earth• Paleontologists study ancient life and fossils

• Fossils are found in sedimentary rock

• Organism gets buried in mud, sand, or clay after they die

• More sediment gets layered over the organism, over time the minerals in the sediment replace the minerals in the skeleton

Dating FossilsDating Fossils

• Relative Dating (stratigraphy) = layers of rocks have different ages, the “youngest” layers on top; older fossils found in older layers of rock

• Radiometric Dating = atoms in the fossil break down at a certain rate, age of the fossil depends on the ratio of atoms to broken down atoms

Geologic TimescaleGeologic Timescale

• Begins with the formation of Earth and goes through present time

• Scale is divided up by the kinds of organisms that lived during that time

• Layers of rock match up with the Geological Timescale

Organization of the GTSOrganization of the GTS

• Broken down into 4 Eras, each era is further broken down into Periods

• The eras and periods are characterized by specific events and specific organisms

• Mass Extinction = many organisms disappear from the GTS almost all at once

4 Eras4 Eras

1. Precambrian Era

• Beginning of the GTS, longest era 87% of Earth’s history

• Oldest rocks are from the Precambrian, oldest fossils too

• First organisms were single celled

2. Paleozoic Era• Cambrian Explosion

occurred during the Cambrian Period

• Enormous increased in diversity of life in oceans

• Organisms with backbones emerged

• Mass extinction occurred at the end of the Paleozoic Era killing off 90% marine life, 70% land life

3. Mesozoic Era• began 248 million

years ago• Dinosaurs died out

during another mass extinction making room for mammals

• Meteor crash could have caused the mass extinction

4. Cenozoic Era• Began 65 million

years ago• Increased diversity in

mammalian life• Modern humans

appeared 200,000 years ago

• As you move towards the bottom of the rock layers, you move back on the Geological Timescale

• Similar fossils found on different continents because at several times in Earth’s history the continents were connected

• Pangea existed 250 million years ago

• Plate Tectonics = the surface of Earth is made up of plates that drift on top of a molten layer of rock

• http://www.nature.nps.gov/geology/usgsnps/animate/PLATES_3.MPG

• http://www.ucmp.berkeley.edu/geology/tecall1_4.mov

The Origin of LifeThe Origin of Life

Ch. 14, Sec. 2Ch. 14, Sec. 2

Spontaneous GenerationSpontaneous Generation

• Pre-17th century it was believed that living things arose from nonliving things through a process called Spontaneous Generation

• 6th century BC: Greek philosophers propose life arose when sunlight was shined onto mud. Why?

• 1600’s: It was believed that mice appeared from rotten grain. Why?

Francesco Redi (1626-1697)Francesco Redi (1626-1697)

• Mid-17th century people believed flies were spontaneously generated from rotting meat

• Redi was a scientist who noticed a life stage to the flies on the rotten meat– 1. Maggots– 2. Pupa– 3. Flies

• He observed that the maggots appeared where flies had landed first

• Redi predicted that if the meat could be kept away from the flies, then there would be no maggots on the meat

• He did not believe that flies spontaneously generated from meat!!!

• So he set up his experiment…

• Control Group = uncovered jar of meat, flies layed eggs, which hatched into maggots, which turned into more flies

• Experimental Group = covered jars of meat, flies have no chance to lay eggs, new flies do not appear

Louis Pasteur (1822-1895)Louis Pasteur (1822-1895)

• Finally disproved spontaneous generation once and for all! 200 years after Redi’s experiment

• Pasteur set up an experiment where boiled broth was exposed to air, but microorganisms couldn’t fall in

• By the 1800’s scientists understood (thanks to the microscope invented a century ago) that microorganisms (bacteria & viruses) caused people to get sick

• But….

• Some scientists still believed that bacteria and viruses spontaneously generated from the air

• Pasteur proved them wrong with his experiment

• Boiled broth was exposed to air in a specially shaped flask over a period of time but nothing grew

• Once the neck was broken off bacteria grew in the broth

• Bacteria did not spontaneously grow from the air!!!

• Thanks to Pasteur….

• Biogenesis = living organisms come from other living organisms

Modern Experiments on OriginsModern Experiments on Origins

• All elements found in organic compounds needed to form biomolecules existed on Earth since its formation

• Early atmosphere contained Ammonia (NH3), Hydrogen Gas (H2), Water Vapor (H2O), Methane (CH4)

• Under high temperature the gases might have formed simple organic compounds (contains Carbon) like amino acids

• When Earth began to cool the organic compounds would have condensed with the water vapor and collected in lakes and seas

Stanley Miller & Harold Urey (1953)Stanley Miller & Harold Urey (1953)

• Recreated the conditions of early Earth in the lab on a smaller scale

• Included chemicals present at the time and an energy source similar to what as present at the time

• Able to generate amino acids (biomolecule)

Alternative HypothesesAlternative Hypotheses

• 1. Life (biomolecules) emerged in ice (Stanley Miller)

• Within ice there are chemicals to create biomolecules & microscopic pockets of water

• Water freezes forcing the chemicals to be close together which increases the chances of chemical reactions occurring

• When the ice melts the biomolecules generated are released into oceans

• 2. Life (biomolecules) emerged in deep sea vents

• Vents provide the heat & chemicals that could cause chemical reactions to generate biomolecules

Formation of ProtocellsFormation of Protocells

• Protocell = Heating the amino acids can cause them to take on some life activities like growth and division

First True CellsFirst True Cells• No direct evidence of the

first cells, scientist can only analyze data that we collect now

• Early Earth had little oxygen, oldest fossils thought to be cells resemble the size & shape of some living prokaryotes, the first cells had organic molecules to eat

• Therefore….

• The first cells were anaerobic, heterotrophic prokaryotes

• Anaerobic = respiration that doesn’t require oxygen

• Heterotrophic = needs to eat other things in order to get the organic molecules needed for life

• Next evolved…

• Autotrophs = make their own food

• Early autotrophs similar to present day Archaebacteria

• Archaea = prokaryote organisms that thrive under harsh conditions, make food through chemosynthesis

• Chemosynthesis = CO2 is the carbon source, energy comes from the use of inorganic chemicals

• Next evolved…

• Photosynthetic prokaryotes

• Autotrophs now able to use sunlight energy to make food

• Created oxygen for the atmosphere which allowed for an increase in diversity of life because now there was an ozone layer (provides protection from UV light)

Endosymbiotic Theory pg. 385 figure 14.15Endosymbiotic Theory pg. 385 figure 14.15

• Lynn Margulis – hypothesis based on experiments and observations

• Proposes that eukaryotes evolved through a symbiotic relationship of prokaryotes.

• Ancient prokaryotes engulfed other prokaryotes and instead of digesting them they survived together.

• Evidence – 1.chloroplasts and mitochondria contain DNA and ribosomes that are similar to the DNA and ribosomes in prokaryotes and unlike DNA in eukaryotic cells. 2. Chloroplasts and mitochondria reproduce independently of cells that contain them.

• This explains why mitochondria has its own DNA