Aim #73: How do scientists explain the development of life on earth?

1) What were the conditions on earth 4.5 billion years ago? Hot Little Oxygen Abundant Lightning 4) Volcanic Activity Harsh Early Earth

2) Primitive Earth’s Energy Source As earth cooled, thunderstorms drenched the earth with water and the oceans formed. Lightning provided an energy source for life to begin.

3) How did life begin on earth? Formation of Organic Compounds Inorganic compounds formed organic compounds. Amino Acids, Nitrogenous Bases, Monsaccharides, Fatty Acids Experiment by Stanley Miller & Harold Urey

4) Formation of Organic Polymers: Scientists have proven that polymers of organic compounds like polysaccharides, polypeptides, lipids and nucleic acids could have formed during the conditions of early earth. “RNA World” Scientists hypothesize that the first genes were RNA. RNA served as the both the molecule that stored the genetic info. & the molecule that directed protein synthesis.

6) Formation of Pre-Cells: Experiments show that membranes can form around organic polymers in a solution if certain kinds of lipids are present. **The simplest living organisms are far more complex than these “pre-cells”

7) Where did life begin? Today’s deep sea vents are populated with simple unicellular organisms that may resemble some of the earliest living cells.

8) First organism on Earth prokaryote cells heterotrophs Anaerobic The first organisms on earth were simple unicellular organisms.

9) Where did the oxygen come from? Some of these early forms of life developed into unicellular autotrophs (they got their energy from the sun and produced oxygen) The first cells were heterotrophs, anerobic prokaryotes. They had to compete for food so what adaptation would help them survive? By what process do autotrophs make their food? What is given off by the process of photosynthesis? So, now what gas do we have in our environment

10) Aerobic Organisms Now, that the new atmosphere had OXYGEN, organisms that could use oxygen to do cell respiration slowly developed.

12) How do scientists explain this change from simple to more complex organisms? Theory of Evolution The process by which species change over time (simple to complex). Present day species are related to ancient species.

12) What is a theory? Theory of Evolution Is an explanation, supported by observations and/or experiments, that can be used to explain related occurrences.

13) What is the evidence that supports the Theory of Evolution? Fossil Record- collection of fossils that provides clues to the history of Earth’s organisms. The fossil record spans much of geologic time (billions of years of Earth’s history). Similarities in Structure Similarities in Development (Embryology) Molecular Biology (DNA & Proteins)

Hint: How do we know dinosaurs existed? 14) How do we know that we have evolved from ancestors distinctly different from us? FOSSILS The fossil record (remains of dead organisms) have given scientists the clues they needed to determine an organisms ancestry by comparing them to present day species. Hint: How do we know dinosaurs existed?

15) The fossil record shows… Life has evolved from simple to more complex Newer Organisms: more complex Older Organisms: more simplistic

16) What do we learn from fossils? http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html How did behaviors evolve? How long did individuals live? How do features evolve over time? http://www.ucmp.berkeley.edu/education/explorations/tours/stories/middle/C7a.html

Speciation 18) Evolution has lead to the formation of new species from different ancient organisms 17) Species- a group of organisms that share certain characteristics & can mate with one another, producing fertile offspring.

Similar to a family tree Descendents Descendents Common Ancestor

Species living at present time (top) Ancestral common species (bottom) 19) Evolutionary Tree Species living at present time (top) Ancestral common species (bottom)

100’s of Millions of year ago Our Common Ancestor Unicellular Common Ancestor 100’s of Millions of year ago

How closely related are they? Which organisms are closely related? Those who have a recent common ancestor (a close point of intersection in a tree diagram) Which are distant relatives? Those who have a distant common ancestor (a far point of intersection in a tree diagram)

20) What organisms are our closest relatives? Why?

Summary of early evolution Present day