Search for signs of life in Episode 71. Do you know the primordial soup recipe?
Search for signs of life in Episode 71. Do you know the primordial soup recipe? (1:05) Melanie recaps the when (1:46) and how (2:38) life may have begun. Scientists have gathered evidence and created models to describe their thinking (4:29).
The Question of the Day asks (7:35) T/F - The first organisms on earth were likely anerobic.
Thank you for listening to The APsolute RecAP: Biology Edition!
(AP is a registered trademark of the College Board and is not affiliated with The APsolute RecAP. Copyright 2021 - The APsolute RecAP, LLC. All rights reserved.)
Website:
EMAIL:
Follow Us:
Hi and welcome to the APsolute Recap: Biology Edition. Today’s episode will recap the origin of life.
Let’s Zoom out:
Unit 7 - Natural Selection
Topic - 7.13
Big Idea: Systems Interaction
On February 18, 2021 - Perseverance touched down on the surface of Mars. The rover immediately sent back images of the surface of the red planet - vast, dry and rocky. One of perseverance’s primary objectives is to conduct astrobiology, searching for signs of ancient microbial life. It will study the planet’s geology and past climate, taking samples from the Martian rock. But what kind of data is it looking for?
Let’s Zoom in:
I know I have it around here somewhere - ah here it is. The recipe for life from primordial soup. Ingredients: carbon, sulfur, nitrogen, hydrogen, phosphorus and oxygen. Mix together in a warm, moist environment. Dry out occasionally. Add time, and energy. Allow to combine in orderly, patterned ways. Eureka! You may have recognized some of those ingredients - CHNOPS - the elements found in abundance in all living things and the building blocks of biological molecules - proteins, carbs, lipids, and nucleic acids.
Once upon a time there was a bang, some would even say it was large, or big. Ok let's call it the Big Bang. Geologic evidence suggests that the Earth formed about 4.6 billion years ago. It was a hostile place to start - hot, lava flowing, sulfuric, little oxygen, and no liquid water! Definitely not a place we would recognize nor optimal for life as we know it today. Yada yada yada - 3.9 bya things started to cool off to support some life - and yada yada yada radiometric dating and we have the earliest fossil evidence for life around 3.5 bya. Microfossils, embedded in rock. Super old. These dates are approximate, but taken all together, we get a plausible range for the origin of life.
Ok so that's the “when” - what about the “how”? Early earth had the inorganic precursors or ingredients that organic molecules could have been synthesized from. There was a lot of free energy and there wasn’t a significant amount of atmospheric oxygen. Deep breath in, and out. Ahhhhhh. Can you believe that oxygen used to be toxic? Oxygen is still oxygen, good ol’ 02, but the earth and consequently the organisms on it, have changed dramatically over time. It should be noted that while the process of evolution explains the unity and diversity of life, the explanation for the origin of life is less clear. And so, scientists have gathered evidence and created models to describe their thinking.
Scientists have tried (many times) to replicate the conditions of early earth in the lab to show how you can spontaneously get complex organic molecules to form. There was Redi with his meat and maggots, Spallanzani with boiled broth, and Pasteur with the swan neck flask. Most notable for abiotic synthesis is the 1953 Miller-Urey Experiment. They combined water, methane, ammonia and hydrogen in a flask - introduced an electric spark (a la lightening) and were able to make simple sugars, fatty acids, and amino acids. Dr. Frankenstein would be proud. This provided the first evidence that organic molecules could be formed from inorganic compounds. There's also the possibility that life was brought to Earth from somewhere else. Perhaps a meteorite containing microorganisms crashed here 3.5 bya and set up shop.
Either way, once you have your organic molecules, they still need to combine into polymers, aggregate together within membranes (perhaps coacervates), develop a metabolism to run the cell and develop a mechanism of heredity. Phew! That sounds like a lot of work. One theory known, as the RNA World Hypothesis, proposes that RNA could have been the earliest genetic material. Single stranded, shorter, and it currently does most of the work (protein synthesis) anyways! RNA can also act as a catalyst, called ribozymes, which supports the idea it may have been self replicating.
Time for unit connections. You can’t appreciate the origin of life without refreshing Unit 1, the chemistry. There is also a connection to Unit 3: Cellular Energetics with the connection to enzymes and Unit 5: Heredity when distinguishing between DNA and RNA. Alright - what about the exam? You do not have to know any of the experiments that are involved in the Origin of life hypothesis. But this is an ideal topic to practice null and alternative hypotheses to explain their work within a prompt. This is science practice 3: Determining scientific questions and methods. It's also a good time for Practice 6: Develop and justify scientific arguments using evidence.
To recap……
Perseverance is searching for answers to life’s big question - is there anybody out there? Elements of life, forming monomers, then polymers and eventually metabolically active cells required very specific environmental conditions. Although the origin of life is less certain, scientists have gathered evidence and created models to describe their thinking.
Coming up next on the Apsolute RecAP Biology Edition: Hardy-Weinberg Equilibrium
Today’s question of the day is about metabolism
Question of the day: T/F - The first organisms on earth were likely anerobic.