Astronomy 141 - Life In The Universe - Autumn Quarter 2009

For many, the most likely place in the Solar System to search for life beyond the Earth is Mars. This lecture describes the properties of Mars, a desert world with a thin, dry, cold carbon dioxide atmosphere. I will review evidence that has begun to point unequivocally to the conclusion that Mars had flowing and standing liquid water on its surface in the past, perhaps during the first billion years or so. If Mars had a warm, wet past, did life also get a start there? Recorded live on 2009 Oct 30 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

Having completed our tour of the Solar System, we now turn to a discussion of the requirements for life, and where those requirements might be satisfied elsewhere in the Solar System. Some - energy, complex chemistry, and liquid water - seem obvious, but they are not the only possibilities or considerations. At the end, we will have a short list of possible places to look, some expected, others surprising. Recorded live on 2009 Oct 29 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

We turn our attention to the Giant Planets of the outer Solar System: the gas giants Jupiter and Saturn, and the ice giants Uranus and Neptune. We will review their structure and properties, and then examine their systems of moons, with special attention to the giant moons. While the Jovian planets themselves seem unlikely places to hunt for life in our Solar System, a few of their largest moons may be more promising than appears at first sight. We'll explore this further in subsequent lectures in this unit. Recorded live on 2009 Oct 28 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

We follow our tour of our Solar System with an in-depth comparison of the Terrestrial Planets. In particular, we want to contrast and compare their geological and atmospheric histories. This will inform our inquiry into whether or not we expect to find life on these worlds. Recorded live on 2009 Oct 27 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 of mammals. We'll look at other mass extinctions during the past 500Myr, and talk about whether extinction-class impacts are in our future. Recorded live on 2009 Oct 22 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 present day from the Cambrian Explosion to the colonization of land by plants and then animals. Most of the lecture will be where most of the time was spent, in the early, microbiological Earth. Recorded live on 2009 Oct 21 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 describe in outline two scenarios that are active areas of origins research: the RNA World model and the Metabolism First model. Finally, I will very briefly mention Exogenesis and Panspermia, which don't really address the problem of abiogenesis so much as move it elsewhere. Recorded live on 2009 Oct 20 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 questions. Recorded live on 2009 Oct 19 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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, you reach the limit if there is no water. Rather than being oddballs, these organisms give us important insights into the origins of life on Earth, and widens the possibilities for life on other worlds. Recorded live on 2009 Oct 16 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 evolution, providing the genetic variation required by natural selection. Understanding the molecular basis of heredity and evolution gives us important insights into the functional requirements for life. Recorded live on 2009 Oct 15 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 State University.

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 elsewhere. Recorded live on 2009 Oct 13 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 of "life" that may best inform us as to how to look for signs of life elsewhere in the Universe. Recorded live on 2009 Oct 12 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 early and late Proterozoic Eon. Recorded live on 2009 Oct 8 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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. Recorded live on 2009 Oct 7 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 this presents the big picture. Recorded live on 2009 Oct 2 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

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 inform us about the nature of science (its successes and failures), and which we will concern ourselves with in the rest of the course. Listeners will note that I do not introduce Evolution (more precisely, Natural Selection) since that is a huge other topic for another day. Recorded live on 2009 Oct 1 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.