EARTH'S FORMATION (LIFE ON EARTH) |BeSci TV
Channel: BeSci TV
Date: 2020-10-18

BeSci TV

EARTH'S FORMATION
LIFE ON EARTH

After having watched the Early Earth video tutorial, we now have an understanding of how Earth’s early atmosphere, crust, and oceans formed. But how about life? When did that evolve and what was early Earth’s life
like?
With a liquid ocean layer present on Earth’s surface, 4.4 billion years ago, the stage was set for the earliest life to ,form. Why were oceans necessary for life? Early Earth had no oxygen in its atmosphere. That means it also had no ozone layer. Ultraviolet radiation from the Sun readily reached the surface and would have irreparably damaged any biological material. Surface waters in the ocean block ultraviolet radiation, and thus oceans are the perfect ,place for life to first form. What were these first organisms like? The very simplest single-celled bacteria – likely ones that could handle extreme conditions, such as high heat and no light – also known as extremophiles.
All living organisms can be classified as autotrophs or heterotrophs. Heterotrophs acquire their food by eating other organisms. Autotrophs make their own food, usually through a process called photosynthesis.
Photosynthesis uses the pigment known as chlorophyll to capture light energy from the Sun, which it then uses to combine abundant surrounding molecules like carbon dioxide and water to synthesize sugar molecules.
Respiration is the opposite process and happens when organisms later break down sugar to release its stored energy and use it for growth, reproduction, and energy-intensive metabolic processes. Whether an organism makes its own sugar or gets its sugar by ingesting other organisms, it still must perform respiration to access the stored energy.
Although photosynthesis is by far the most common form of sugar synthesis at work on Earth today, another process at work where light is absent is called chemosynthesis. Instead of harnessing energy from the sun, chemosynthesis harnesses energy held within chemical bonds of gases and minerals. We see chemosynthesis happening today in a number of dark locations, including deep in underground mines, at the bottom of the seafloor where gases seep out of cracks and sediments, and in caves near sulfur-rich mineral deposits. In all these locations, autotrophs use energy to combine surrounding ingredients and form sugars. Any of these locations could have been the cradles in which early life formed on Earth.
In South African gold mines, in shafts nearly 3 km underground, at temperatures as hot as 120°F or 49°C, there are colonies of bacteria surviving without sunlight or oxygen, making their own food from energy stored in chemicals in the rocks, like iron. Other species of bacteria have been found deep in mine shafts and in 1,000-mdeep volcanic rocks along the Columbia River. In limestone caves, near volcanic sulfur-rich hot springs, bacteria capture energy from hydrogen sulfide gas and use that energy to synthesize sugar. Sulfuric acid is one of the toxic byproducts, and these bacteria live in highly acidic mucous-rich mats attached to the cave walls. The mats are called snottites. This example is from Cueva de Villa Luz in Tabasco, Mexico. These snottites have acid drops at their tips, with a pH of 0.
In hydrothermal vents and hydrocarbon seeps on the bottom of the seafloor, bacteria capture energy from
hydrogen sulfide or methane gases and use that energy to synthesize sugar. These bacteria provide the base of an
exotic and diverse food web.