The Earth is estimated to be approximately 4.6 billion years old. For its first 2 billion years, its atmosphere lacked oxygen, which is necessary to support life as it is currently known.

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- Genetics
- Cell theory
- Evolution
- Homeostasis

Foundations of Modern Biology

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

The process in which physical/behavioral changes of a population occur over long periods of time. Evolution is a scientific theory that for over the last 150 years, scientists have gathered an overwhelming amount of evidence that supports this theory.  

Evolution 

The scientific field of study of traits and their passage from parents to offspring. Humans inherit 23 chromosomes from the father, and 23 from the mother. These 23 pairs of chromosomes consist of 22 autosomal chromosome pairs and one sex chromosome pair. The physical unit of inheritance is a gene, comprised of DNA (Deoxyribonucleic acid) segments.

Genetics and Inheritance in Humans

Developed in the 17th century following early observations of microscopic life, the cell theory is a foundational scientific principle. It posits three main claims: the cell is the fundamental unit of life, all living organisms contain at least one cell, and new cells can only arise from pre-existing cells.

Cell Theory

The Earth's Early Atmosphere

The primordial soup hypothesis proposes that life on Earth began in a body of water. According to this idea, metals and gases from the atmosphere combined with an energy source—such as lightning or ultraviolet light—to form the organic carbon compounds that serve as the chemical building blocks of life.

Primordial Soup Hypothesis

In 1952, Stanley Miller and Harold Urey conducted an experiment to test the primordial soup hypothesis by simulating the early Earth's atmosphere. They combined water ($$\text{H}_2\text{O}$$), methane ($$\text{CH}_4$$), hydrogen ($$\text{H}_2$$), and ammonia ($$\text{NH}_3$$) in a sealed, sterile flask, heated the mixture to generate water vapor, and introduced electrical sparks to simulate lightning. After one week, they analyzed the contents and discovered amino acids, which are the structural units of proteins.

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