So far, we have looked at possible life-supporting exoplanets. As of yesterday, the oldest Earth-sized planet, currently named Kepler-444, we know of in the Milky Way is over 11 billion years old. For the rest of this course, we will focus our attention towards life on our planet, Earth. Our Earth is a youthful 4 1/2 billion years old. We know its age because the oldest rock on its surface has been found in Jack Hills, Australia. Zircon 74 is 4.37 billion years old. Formed a mere 160 million years after the formation of the solar system, its ancient existence proves that almost as soon as the Earth formed, there were seas if not oceans of liquid water on its surface, one of the essential building blocks of life.
Geologists have delineated different Eons, Eras, Periods, and Epochs of the Earth’s life to help identify key stages in the evolution of life on this planet.
The zircon crystals mentioned above were formed in the Archean Eon (3.8 — 2.5 billion years ago). Before the end of the Archean Eon, life had been established through the planet. Stromatolyte fossils have been dated back to 3.5 billion years ago.
The Miller-Urey experiment is a way of showing how early life on Archean Earth may have been formed. This experiment is one of the fundamental chemical reactions included in the study of exobiology. That is, all of the the chemical reactants used to produce amino acid products are known to exist in outer space. An alternative hypothesis for the origin of life is that these chemical reactions occurred miles below the Earth’s surface, where thermophiles and extremxozymes lurk.
The beginning of the next Eon, the Proterozoic, offered evidence of new biochemical reactions, primarily resulting in vast ranges of banded iron, the diagenesis of iron minerals throughout the Earth. “Snowball Earth” then ensued. And yet, 100 million years later, 635 million years ago, life not only survived, but diversified into multicellular organisms, in the Ediacaran Period.
Each of the millions of Earths in our Milky Way galaxy has its own epochal story to tell, if we ever set foot on them. For now, we are limited to exploring the stories our own Earth has to tell.
We ended class in the Ediacaran Period.
- Working in pairs, choose another, more recent period to research.
- Type in your choice as a comment to this post (first comment gets it)
- Begin researching the forms of life that existed on Earth during that period of time. Post any interesting websites as additional comments.
- Organize your research by the 7 Properties of Life defined on page 2 of your textbook (Miller, 7th Ed.)