Origin History of Life on Earth Patricia Princehouse

Origin & History of Life on Earth Patricia Princehouse Case Western Reserve University Cleveland, OH evolution@case. edu

Origin & History of Life on Earth The Earth coalesced about 4. 6 billion years ago (bya) & was then hit by a Mars-sized planet, Theia.

Origin & History of Life on Earth Moon: 4. 53 bya

Origin & History of Life on Earth The Earth was molten for hundreds of millions of years

Origin & History of Life on Earth Eventually the Earth cooled enough for rocks to solidify and continents to form. www. physorg. com/news 8341. html

Origin & History of Life on Earth Life appeared about as early as it could have, perhaps originating as early as 4. 1 bya. Microscopic fossils of singlecelled organisms appear around 3. 8 bya, and structures like these stromatolites are present by 3. 5 bya.

Origin & History of Life on Earth But how did it happen?

Origin & History of Life on Earth One hypothesis (exogenesis) suggests that bacteria-like organisms came to earth from outer space. Another (panspermia) holds that many of the building blocks of life drifted in from space but that those components combined here on earth (along with components produced here) to give rise to early life. http: //www. dailygalaxy. com/photos/uncategorized/2007/11/28/astrobio_2. jpg

Origin & History of Life on Earth But most origin of life researchers think life evolved in situ on earth from molecules produced here.

Origin & History of Life on Earth Life today is built on a biochemical foundation of RNA and DNA. One school of thought looks for molecular candidates that may have been simpler precursors to RNA, such as TNA (threose). At any rate, some molecule developed the ability to make copies of itself–it became a replicator.

Origin & History of Life on Earth But the replicator is not enough. There additional components necessary to produce the earliest cells. Of crucial importance is a system for housing the replicator, leading candidates include clay bubbles and fatty acid spheres. Both form spontaneously and would have provided a protective surface on which the replicators could reproduce.

Origin & History of Life on Earth At first, these protocells would probably burst when they became too big, and the RNA would attach to other bubbles. But in time the membrane strengthened and the RNA developed more sophisticated capabilities. You can learn more about these properties in journals, books & on the internet. Scientists disagree as to at what point the developing protocell crossed the line to what we would want to call life.

But eventually cyanobacteria like these were produced and began to form colonies such as stromatolites

Origin & History of Life on Earth About 2. 5 bya, symbioses of these simple cells produced nucleated cells, such as those in this fossil, and photosynthesis evolved. This created large quantities of free oxygen and changed the earth’s atmosphere forever.

The Diversity of Life

Origin & History of Life on Earth Around a billion years ago, the earliest animals evolved. They were like sponges.

Early multicellular organisms with specialized functions first appear in the fossil record some 600 mya

Beginning around 535 mya, we begin to see the familiar phyla of animals appear.

Around 380 mya, the first tetrapods evolved from fish. Primates evolved about 55 mya, and bipedal human ancestors appear beginning around 6 mya.

Which brings us to the present day…

Thanks! Patricia Princehouse Case Western Reserve University Cleveland, OH evolution@case. edu