The History of Life on Earth

Grand Canyon

Earth’s Early History How did the Earth form? – Scientists must explain past events in terms of processes that they can observe. Charles Lyell Why did the Earth form? – This question is outside of the realm of science.

Earth’s Age Over 4,600,000,000 years old. – First trace of Humans dates to about 1.8 million years ago. More than 99% of all species that have ever lived have become extinct.

Ohio’s Fossil

The Fossil Record Provides evidence about the history of life. Shows how organisms have changed over time.

The Fossil Record Radioactive Dating – Calculate age of sample based on amount of remaining radioactive isotope it contains based on the isotopes half-life. Relative Dating – The age of a fossil is determined by comparing its placement with that of fossils in other layers of rock.

Earth’s Early Atmosphere

Probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water. – If you were to travel back in time, after a few short breaths you would no longer exist.

Earth’s Atmosphere Earth was formed 4.6 billion years ago. Around 3.8 billion years ago changes occurred in Earth’s atmosphere. Water could remain a liquid on the planet.

Earth’s Atmosphere

First life found to be around 3.5 billion years old. What type of life? – Single-celled prokaryotic ancestors of modern bacteria. Little to no oxygen present in Earth’s atmosphere. How is this possible? – Chemosynthesis.

Earth’s Atmosphere 2.2 Billion Years ago Organisms began producing oxygen, an end product of? How could this be? – Observation of Oxygen reaction with iron and water. Many rust deposits in rocks dated to this time.

Rusty Rocks

Earth’s Atmosphere Organisms churning out Oxygen What would this do to the atmosphere? – Oxygen increase, methane and hydrogen sulfide concentrations decreased. What would this do to the microbes on Earth? Remember we are talking about BILLIONS of years!!

The Increase in Oxygen Poisonous, reactive gas. Peace early life forms. Hello life forms equipped to use oxygen in their metabolic pathways. – Respiration

The Increase in Oxygen Stage set for the gradual transition to “modern” life and the gradual transition to modern atmosphere. – Oxygen increase in the atmosphere took over HALF A BILLION YEARS! – Descendants of early anaerobic life forms still exist today. – Use other chemicals such as nitrates and sulfates for metabolism.

Origin of Eukaryotic Cells

2 billion years ago. Internal cell membranes began developing in prokaryotes. Ancestral eukaryote engulfed prokaryotes.

Origin of Eukaryotic Cells Endosymbiotic theory – Eukaryotes engulfed and formed a symbiotic relationship with prokaryotic organisms. Engulfed prokaryotes are modern day chloroplasts and mitochondria. – Mitochondria and Chloroplasts share many similarities with free-living bacteria.

Origin of Eukaryotic Cells

Geologic Time Scale

Macroevolution Macro? – Big Evolution? – Change over time. Macroevolution – Large scale evolutionary changes that take place over a long period of time.