The Beginning of the Earth Evolution Chapter 17

The Beginning of the Earth Evolution

Chapter 17 Earth was formed 4. 5 billion years ago – Fiery ball of molten gases – Cooled and formed rocky crust – Water vapor in atmosphere condensed to form oceans

Life on Earth Ø It took hundreds of millions of years to start

Earth’s Age Determined by: ØRadiometric dating- measuring certain elements in rocks ØRadioactive isotopes give approximate age of rocks ØHalf-life- time it takes for ½ of a given amount of an element to change into another isotope

Chemicals For Life • Scientists believe life started from nonliving matter which reacted chemically to form simple organic compounds – Sunlight and volcanic heat combined the compounds to make more complex compounds which eventually became the first cell – Has been simulated in the lab

Primordial Soup • Oparin and Haldane theorized that at one time the oceans were full of different organic molecules which chemically reacted with solar radiation, volcanic eruptions, and lightning • Miller and Urey tested theory in lab and made amino acids, fatty acids, and hydrocarbons (basic chemicals for life) • Today we question theory because chemicals to form life were not in atmosphere

Bubble Model Louis Lerman in 1986 • Ammonia, methane, and other gases trapped in bubbles in the ocean • Chemical reaction takes place in bubble • Bubbles release organic compounds to air • Wind exposed compounds to ultraviolet radiation and lightning • Complex organisms fell to oceans with rain

Organic Chemicals Become Complex Scientists agree to disagree on theory • Agree that energy needs to be present • Have made short chains of RNA in lab but not DNA yet • RNA could have acted as the first catalyst to assemble the proteins • Short chain of amino acids form a microsphere • Linked amino acids are coacervates

Life? • Microspheres are not considered living until they can transfer characteristics to offspring • We think that RNA evolved into DNA

Prokaryotes • Oldest fossil of prokaryote is 3. 5 billion years old • Also known as bacteria • Single celled • Lack internal membrane-bound organelles • Was photosynthetic • Released oxygen and changed the atmosphere over time

2 Types of Prokaryotes • Archaebacteria • Lack peptidoglycan in their cell walls • The first type of life • Are what eukaryotes evolved from • Eubacteria • Contain peptidoglycan in their cell walls • Same type of DNA as mitochondria and chloroplast organelles in eukaryotes

Cyanobacteria • The first type of prokaryotes to appear • They are photosynthetic • Gave off oxygen to form today’s atmosphere • They still exist today

Eukaryotes • 1. 5 billion years ago- eukaryotes appeared • Have internal membranes • DNA in a nucleus • Organelles called mitochondria and chloroplasts

The Theory of Endosymbiosis • Proposes that mitochondria evolved from symbiotic, aerobic eubacteria, and chloroplasts evolved from symbiotic cyanobacteria – Once controversial, but now is widely accepted by scientists – First presented in 1966, by American biologists – Supporting evidence includes: • Similar size between mitochondria, chloroplast, and bacteria • Similar genetic material (DNA) • Similar method of reproduction • Similar ribosome structure

The 6 Kingdoms 1. 2. 3. 4. 5. 6. Archaebacteria Eubacteria Protista Fungi Plantae Animalia • Appeared in the order they are listed • Archaebacteria and eubacteria are prokaryotes • Protista, fungi, plantae, and animalia are eukaryotes

Earth’s Atmosphere Past • N 2 Nitrogen • H 2 Hydrogen • H 2 O Water • NH 3 Ammonia • CH 4 Methane Present • N 2 Nitrogen • O 2 Oxygen • Traces of others

Mass Extinctions Have a Major Impact • • Mass Extinction- death of all members of many different species, usually caused by a large (world wide) ecological disaster, such as geological or weather changes There have been 5 so far and the dinosaurs died out in the last one Scientists believe we are currently experiencing another Extinctions make food and living space (niches) available for surviving species, which will prosper and grow in numbers

Life Moves to Land • Early life started in the ocean because the conditions of land were too harmful • Ultraviolet radiation from the sun made it impossible to live on land • The increasing amounts of 02 (from cyanobacteria) formed ozone (O 3) in the upper levels of the atmosphere which blocks most of the dangerous UV light, making it safe to live on the land

Plants and Fungi on Land 1 st • They formed a symbiotic (mutualism) relationship, where both organisms benefit • Plants to provide nutrients via photosynthesis • Fungi to provide minerals from bare rock (not soil yet) • Eventually (millions of years) the bare rock that covered the Earth was broken down into soil

Arthropods Crawled out of the Sea • The 1 st animal to live on land • Biologists think that it was a type of scorpion • Examples of arthropods today are lobsters, crabs, insects, and spiders (they have exoskeletons)

Next on Land Came the Vertebrates • Vertebrates are animals with a backbone • The 1 st were small, jawless fishes that evolved 500 million years ago • Next evolved jawed fishes, 450 million years ago (very successful) • The 1 st land vertebrates were amphibians

Amphibians on Land • They were smooth skinned animals that include frogs, toads, and salamanders • Could survive on land because: – Had lung sacs – Developed limbs from fins – Strong skeletal system to walk with

Reptiles Evolved from Amphibians • Happened about 350 million years ago • Developed water-tight skin • Gave reptiles the advantage over amphibians

Reptiles Became Abundant • Reptiles became the most abundant vertebrates until the 5 th extinction • The extinction of most reptiles opened the door for birds and mammals to thrive