History of Life on Earth Chapter 14

Early History of Earth *Earth is 4.5 to 4.6 billion years old *Evidence of life appears in the fossil record 3.5 bya (billion years ago) *Primitive Earth = inhospitable environment; very hot, numerous volcanoes, very little free oxygen, combination of methane, ammonia, water vapor, carbon dioxide and nitrogen.

Dating of Earth & Fossils Relative Dating: the oldest fossils are found in the bottom layers, while the youngest fossils are found in top layers Fossils form best in what type of rock?

Dating of Earth & fossils Radiometric dating or Carbon Dating: used to estimate how long ago rocks formed and the age of fossils contained within those rocks Radioactive isotopes that are unstable decay over time into stable elements.

Dating Fossils: Radiometric Dating Each radioactive isotope has what is called a “half- life” (the amount of time it takes for ½ of the original isotope to decay) Example – C-14 has a half-life of 5, 730 years. (Carbon 14 to Carbon 12) By measuring how many half-lives have passed since a rock was formed, scientists can estimate the rock’s/fossil’s age Also Uranium decays to lead Potassium

Let’s watch!

Relative vs Absolute time

The Geologic time scale!!!! BF1F7DA180 Page 397 http://www.glencoe.com/ose/showbook.php Time Scale

Need to know Geologic Time The earliest era when life began is Precambrian First Vertebrates appear in the Paleozoic Era This is called the Cambrian Explosion Stromatolites (the cyanobacteria) helpled put oxygen on earth

Spontaneous Generation The thought that life arises from non life Can a fly come from a desk or a frog literally from a pond: NO!! Disproved first by Fransico Redi: Meat experiment

Biogenesis!!! Biogenesis: Life comes from pre-existing life. Proved by Louis Pasteur

Origins of Organic Molecules “Primordial Soup” – Oparin suggested life began in the seas – Miller & Urey tested: * simulated early conditions on earth’s atmosphere: water, methane, ammonia, hydrogen * circulate atmospheric gases by boiling and condensing the water * sparked with electricity (lightning) * end result = produced amino acids, fatty acids and other hydrocarbons

Bill and the Urey Theory!

Origins of Organic Molecules Possible Reactions 2) “The Bubble Model “ – Louis Lerman (1986) suggested : *Gases from undersea volcanic eruptions were trapped in underwater bubbles * chemical reactions occur inside bubble, formed organic molecules * bubbles rose to the surface & burst, release simple organic molecules into the air – more energy from the environment ( UV radiation & lightning) * end result = formed complex organic molecules that fell into ocean with rain

Origins of Life 3.5 bya in fossil record -PROKARYOTES appear (used organic molecules as “food”) Competition for limited food led to the photosynthetic bacteria = cyanobacteria (that released oxygen into atmosphere) Allowed the ozone (O3) to form – protective shield to allow life on land EUKARYOTES arose next (1.5bya) BUT HOW???

Endosymbiont Theory (Origin of Organelles) ■Explains how eukaryotes may have arisen ■Aerobic bacteria were “engulfed” by larger bacteria (formed a symbiotic relationship) ■Over time, developed into the MITOCHONDRIA

Endosymbiont Theory ■Separately, photosynthetic bacteria were also “engulfed” ■Over time, became the CHLOROPLASTS

Evidence to support Endosymbiosis: Mitochondria & chloroplasts have their own DNA – similar to bacteria machinery Both can replicate independently of cell division Both have ribosomes similar to bacteria Size & structure of each is similar to bacteria

Endosymbiont Theory Founder Founded by Lynn Margulis Dr. Margulis was best known for demonstrating a theory of biological change, called the endosymbiotic theory, that appears to suggest a degree of cooperation between organisms. Died 2011 founded theory in 1970 with book “Origin of Eukaryotic Cells” Theory Animation

Geologic Trip through Time 4 eras in Earth’s history – Geologic Time Scale Era End Date Calendar Year Analogy Precambrian 544 mya Jan - Mid-Oct (87% of history) Paleozoic 245 mya Mid-Oct - Early Dec Mesozoic 65 mya Dec 10th – late Dec. Cenozoic present Dec 26th - Dec 31st

Origin of Prokaryotic and Eukaryotic Cells Use the terms and phrases below to complete the concept map. Chloroplasts Cyanobacteria Endosymbiosis Fossils Life on land Mitochondria Ozone Prokaryotes 3.5 bya eubacteria

Origin of Prokaryotic and Eukaryotic Cells Use the terms and phrases below to complete the concept map. prokaryotes Chloroplasts Cyanobacteria Endosymbiosis Eubacteria Fossils Life on land Mitochondria Ozone Prokaryotes 3.5 bya cyanobacteria eubacteria fossils chloroplasts mitochondria 3.5 bya ozone endosymbiosis Life on land

Now time for a webquest… Visit the following website and complete the webquest! Life Has a History – CLICK HERE!