HISTORY OF LIFE Chapter 14

The Record of Life Ch. 14, Sec 1

Early 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 breathe 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 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 Fossils Relative Dating = 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 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 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 All eras are NOT the same length of time! Mass Extinction = many organisms disappear from the GTS almost all at once

4 Eras 1. Precambrian Era 4.6 BYA - 580 MYA (4,020,000,000 years long) 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 580 MYA – 248 MYA (332,000,000 years long) 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 248 MYA -65 MYA (183,000,000 years long) Era of the dinosaur 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, continues today 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 Life Ch. 14, Sec. 2

Spontaneous 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) 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

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

First 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 Eukaryotic cells evolved from Prokaryotic cells Symbiosis = close, long term relationship between species An ancient prokaryote engulfed another prokaryote and instead of digesting it they lived together

This explains why mitochondria has its own DNA and a double membrane

http://highered. mcgraw-hill http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter4/animation_-_endosymbiosis.html