This first lecture of Unit 4 - Life in the Solar System - is a quick tour of our Solar System reviewing the planets, dwarf planets, moons, and small bodies that make up our celestial home. This lecture will introduce many of the places we will be considering in detail over the next two weeks, and which we'll find around other stars. Recorded live on 2009 Oct 26 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

We end our exploration of life on the Earth with a look at death in the fossil record. This lecture looks at the role asteroidal impacts have played in the history of the Earth, and their possible role in mass extinction events in the fossil record. We will discuss near-earth asteroids, historical impacts, and the K-T event in which a massive asteroid impact caused a mass extinction of species that included all non-avian dinosaurs among its victims, opening up the biosphere to the dominance...

In this lecture we step back and look at the history of life on Earth from the first signs of life at start of the Archaean Eon 3.5 billion years ago to just up to the present day. We will review the appearance of photosynthesis and the rise of oxygen in the atmosphere in the Proterozoic, the appearance of the first eukaryotes and sexual reproduction, and the Cambrian explosion of plant and animal species at the start of the Phanerozoic Eon, and briefly review the changes in life to the...

How did life arise from non-life? Frankly, we don't know, but current experimental work is aimed at trying to understand how it might work in biochemical terms. This lecture sets out the problem of "abiogenesis", and describes our current thinking about the likely origins of life on Earth. We will review the classic Miller-Urey experiment, and look at its insights and limitations, discuss meteoritic sources of amino acids, and the basic requirements needed for protolife. I will then...

What are the first recognizable forms of life that we find in the geological record? How far back can we go in geological time and still find life? This lecture reviews three lines of evidence that have emerged in recent years to suggest that life may have emerged very early on the young Earth, perhaps within a few hundred million years of the end of the epoch of heavy bombardment. I will describe fossil stromatolites, microfossils, and carbon isotope data that are used to explore these...

Extremophiles are organisms that are adapted to survive in extreme environments. This lecture describes the challenges that extremes of heat, cold, acidity, salinity, and radiation pose to organisms, and show examples of how evolution has nonetheless allowed some organisms to adapt to not just survive but thrive in such extreme conditions. Finally, we will explore the possible limits of life on Earth, and find that while you can make things pretty extreme and still have organisms adapt,...

DNA and RNA are the key molecules of living cells. DNA plays a vital role in storing and transmitting the hereditary information that constitutes the "operating instructions" of living cells; how to construct the functional and structural proteins that perform vital cell functions, control developmental pathways, and basically "build" the organism. RNA is the crucial actor in protein synthesis and other cell functions. Mutations, changes in the DNA coding, are the molecular basis for...

What is the basic chemistry of living organisms? We introduce the requirements for metabolism (raw materials and energy), the ATP/ADP energy cycle in cells, auto- and heterotrophs, photosynthesis and chemosynthesis, and the role played by liquid water. The goal of today's lecture is to seek insights into the basic requirements for life from a consideration of the needs of the cells' chemistry. Recorded live on 2009 Oct 14 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio...

Cells are the basic structural and functional unit of all life on Earth. This lecture reviews the basic building blocks of cells, the main chemical components, the two basic types of cells (Prokaryotes and Eukaryotes), and introduces the Phylogenetic Tree of Life, the way biologists order life by their biochemical and genetic relationships. Understanding life at the cellular level gives us important insights into the nature and history of life on Earth, and clues as to what we might look for...

How do we define life? This lecture reviews the six basic criteria for living systems described by biologists: order, reproduction, growth and development, energy utilization, reaction to environment, and evolution that characterize life. The last third of the lecture is an admittedly whirlwind review of natural selection (I got off my stride and got a little rushed for time at the end). The goal is not a complete survey of current biological thought, but to highlight those characteristics...

What are the main mechanisms of climate regulation and climate change that have operated through Earth's history? The Earth's climate is regulated by a Carbon Dioxide thermostat that is the interaction between the Greenhouse Effect and the CO2 Cycle. I describe the CO2 cycle and its role in regulating global temperature. I will then discuss other influences on climate, and periods of glaciation (ice ages) in the recent and distant past, including the possible Snowball Earth events in the...

How have we pieced together the geological history of the Earth? This lecture reviews the different types of rocks and the cycle of transformation between them, with particular emphasis on stratigraphy. I will outline the 4 major Eons in Earth's history, and focus on the earliest Hadean Eon which proceeded from the formation of the Earth to the end of the epoch of Heavy Bombardment. The Hadean Eon saw the formation of the primordial atmosphere of the Earth and the formation of the Oceans....

This lecture was to be about the Earth's atmosphere, its composition and structure, the greenhouse effect, and the primordial atmosphere, but about 2 seconds into the lecture, unbeknownst to me, the battery compartment on my digital voice recorder came open in my pocket. At the end of lecture, I took it out of my pocket to turn it off and the battery didn't come with it. Oops! Fail. My apologies, I'll put in some work to prevent a recurrence in future lectures. Recorded live on 2009 Oct 6...

What is the interior structure of the Earth and how does it drive the Earth's magnetic and geologic activity? We will review our current knowledge of the interior of the Earth, how we measure it using Seismology, the origins of the Earth's magnetic field, and discuss the workings of plate tectonics. the Earth is a dynamic, geologically active world, which has interesting implications later for understanding the past and future history of life on Earth. Recorded live on 2009 Oct 5 in Room...

Cosmology is the study of the entire Universe as a physical system. The past century has witnessed a revolution in cosmological thought that has revealed the vastness of space and the depths of cosmic time, a revolution that is still playing out in the present day. The lecture will review the Earth's place in the Universe, the age of the Universe as reckoned by the time since the Big Bang, and the origin of the elements. We will return to many of these topics later in the course, but...

What is the nature of life? In this lecture I will review the revolution in biological thinking that has dramatically changed how we view life. I will review such persistent ancient ideas as spontaneous generation and why it took so long to disprove this notion, the impact of the microscope on biology, and the discovery of the laws and agency of heredity. This is obviously a highly-selective view of a vast topic, and my goal is to highlight those episodes in the history of biology that...

The geological revolution revealed that the Earth is of great antiquity and yet has a history we can read in the land. We will discuss ideas of cyclic and linear time, historical versus physical age estimates, the discovery of geological time, and radiometric dating methods that give us our present estimate of 4.54+/-0.05 Gyr for the age of the Earth. Recorded live on 2009 Sep 30 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

What is the nature of matter, and how did we come to understand the chemical elements and atomic structure? This lecture is a brief and selective overview of the history of our understanding of the nature of matter and chemistry. We will also introduce spectroscopy and radioactivity, two very powerful tools that came out of the chemical revolution that are crucial for the inquiry in this class into the question of life on other worlds. Recorded live on 2009 Sep 29 in Room 1005 Smith...

Modern science was borne of an effort over many centuries to understand the motions of celestial bodies. The Copernican Revolution of the 16th and 17th centuries was the crucial moment in history when we finally understood the nature of celestial motions, and opened the door to the modern world. This lecture reviews the problem of celestial motions, the two competing models for explaining them, and the final revolution in thought starting with Copernicus and ending with Newton. ...

What is the cultural history of our imaginings of other worlds and their possible inhabitants? I will draw examples from history, philosophy, literature, cinema, and popular culture. In the end, our imaginings about other worlds inform us more about ourselves, our hopes and our fears, than about extraterrestrial life. The scientific inquiry we are undertaking must therefore approach the problem from a different direction. Recorded live on 2009 Sep 25 in Room 1005 Smith Laboratory on the...

An introduction and review of the basic notation and physical units we will be using throughout this course. In particular, we will be using the Metric (SI) system for lengths, masses, times, and temperatures, and special astronomical units for distances (AU and Light Years) and masses (Earth Masses and Solar Masses) appropriate when discussing interplanetary and interstellar scales. Recorded live on 2009 Sep 24 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

A brief overview of the topics we will cover in Astronomy 141, setting the stage for how we can make a serious scientific inquiry out of the question of whether or not there is life elsewhere in the Universe. It is a short lecture, the first half was an overview of course mechanics (tests, homework, office hours, etc.) that I did not record. Recorded live on 2009 Sep 23 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

Welcome to the Astronomy 141 Lecture Podcasts. This is a brief message from me explaining the podcasts, and welcoming new and old listeners. University. Lectures will begin on Wednesday, 2009 Sept 23, and run through Friday, 2009 Dec 4. New lectures will appear shortly before 6pm US Eastern Time each day there is a regular class. Recorded live on 2009 Sep 23 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.