So far, we have considered how broad the definition of life is, inhabiting moons and planets in our solar system, at least 10,000,000 exoplanets in our Milky Way galaxy, one of 176 billion galaxies in a universe 13.8 billion years old. We can analyze the light of the 10,000 billion billion stars around our Earth, measuring their spectri to identify the chemical precursors for life, chemicals that react with each other to yield energy for sustaining life, even without light or oxygen. Life can thrive on Earth three miles deep in our oceans near hydrothermal vents spewing arsenic and sulfuric acid at 250° F. We can draw lines in the sands of 4 ½ billion years of time, marking geological periods of the Earth’s time in this universe. Scientists know these facts from using space telescopes, geologic strata, carbon-14 dating, and DNA clocks.
How can scientists possibly make sense out of 4 billion years of life on Earth? Life formed from carbon and oxygen fused from hydrogen in stars that lived and died billions of years before the Earth even existed? Why was our world dominated by stromatolites for a billion years, only to recede to the acidic aquatic corners of the Earth, followed by millions of other species, who ruled the world in their day as well, only to disappear many millions of years ago, until, finally and contingently, our time on Earth began? A common way to make sense of such an immense structure is to apply some organizing principles Boricua students are already skilled with:
4.0 Analysis. Analysis refers to the ability to break down material into its component parts so that its organizational structure may be understood. This may include the identification of the parts, analysis of the relationships between parts, and ecogrnition of the organizational principles involved. Learning outcomes here represent a higher intellectual level than comprehension and application because they require an understanding of both the content and the structural form of the material.
The big topic tonight will about the “Tree of Life.” Biologists have organized all living things into several “kingdoms,” each which possess several unique characteristics:
- Animalia — obtain energy from other organisms
- Archaea — many live in extreme environments
- Bacteria — lack a cell nucleus and organelles
- Chromista — chlorophyll c, no starch. Brown pigments
- Fungi — a system of filaments which produce spores
- Plantae — produce their own food through photosynthesis
- Protista — unicellular, complex internal structures and carry out complex metabolic activities.
- Viruses — small infectious agent that can replicate only inside the living cells of an organism
From these fundamental categories, further delineations can be made by using a taxonomy hierarchy (kids prefer cheese over fried green spinach):
Using this structure, we can place living and extinct species into one massive organizing structure, usually through a dichotomous key. Several websites listed below attempt to document the ongoing efforts of scientists to complete this endeavor.
- Encyclopedia of Life (reference resource)
- Tree of Life (work backward)
- Catalogue of LIfe (work forward)
Cladograms of species, like karyotypes, allow us to spatially arrange pieces of information to tell a larger story. Life change over the geological history of Earth — early on, the first living things developed into three categories, or domains, known as Bacteria, Archaea and Eukarya. In later geological periods, each of the Domains developed subdivisions, or Kingoms, one of which circumscribes all animals (Animalia). Here’s how the entire classification process works. And here are 3 examples.
- Go to the PBS NOVA Evolution Lab. Follow the instructions to complete the six phylogenic trees. When you finish one, print out the complete screen like the one below for credit. Make sure the date is printed out on the page (if it’s not I won’t accept it), and write your name on it.
- Use the Encyclopedia of Life, Tree of LIfe, Catalogue of Life to determine the place of your group’s prehistoric organism in the Tree of Life.
- Complete the Genetic Disease Worksheet.
- Once the professor says your Genetic Disease form is completed correctly, do another.
- Find a news article about thermophiles or extremephiles.