History of Life on Earth
.docx
School
Lafayette High School, Lafayette**We aren't endorsed by this school
Course
SCI 23
Subject
Biology
Date
Dec 16, 2024
Pages
2
Uploaded by GrandEaglePerson1252
History of Life on EarthHow did Life Originate on Earth?Earth is the only place in the Universe that we know has life. The exploration of life’s origins on Earth has generated much philosophical and scientific _______________ over the centuries. Because no one was around to observe life begin and the fact that fossilized evidence for life is scant. However, scientists have done experiments _______________the conditions present on Earth and determined that the proteins necessary for living organisms can form in these environments. The exact date that life began on Earth is up for debate, with the earliest date being a mere 250 million years after Earth’s _______________, while the oldest fossils of microorganisms date to about 3.5 billion years ago.What was the Cambrian Explosion?It took a long time for life to establish a _______________ on Earth, and only 1 billion years ago the earliest plants were beginning to appear on land. By 500 million years ago, living organisms were mostly small and not very _______________. During the Cambrian period (540-485 mya), life exploded in terms of amount, variety, and complexity, with all _______________ animal phyla present. The oceans of Cambrian Earth were teeming with all sorts of life including the first vertebrates that swam along the ocean floor. There are many competing theories as to why this occurred, but some studies show that around the time of the Cambrian period, _______________ levels in both the atmosphere and oceans reached levels close to today’s levels, allowing modern organisms to grow and thrive.How did Modern Plants Evolve?Plants initially appeared around 800 million years ago in the form of green _______________. Algae would form mats that would float at or near the surface and continued to do so until the Ordovician period (485-443 mya) when primitive phyla like modern _______________ and moss began to appear on land. Fossil evidence shows that plants only established themselves away from the coasts once they developed methods of holding onto water. Seedless plants like ferns dominated most of the Paleozoic era, but plants that reproduced through seeds appeared in the late Devonian period (416-359 mya) and took over in the Mesozoic era. _______________ plants (Angiosperms) first appeared in the Jurassic period, and only became dominant during the Cretaceous period (145-66 mya).How did Vertebrates Evolve?Invertebrates may make up nearly 95% of all animal species, but vertebrates are what we tend to associate with animals, and since humans are vertebrates, it makes sense to explore their origins. The first vertebrates appeared duringthe Cambrian explosion, and while they had a spinal cord enclosed in a _______________, they did not have any jaws. Skeletons evolved throughout the Ordovician period and exploded during the Devonian period (416-359 mya), also called The Age of _______________. Fish classes developed jaws and skulls with a cartilage skeleton, and later a fully bony skeleton. Late in the Devonian period fish developed more advanced lungs as well as a different form of fin: a muscular and bony _______________. Eventually these lobes developed into muscular limbs, and the first _______________ began to establish a permanent presence on land. By the Carboniferous period (358-299 mya), amphibians ensured that vertebrates lived on land and water.What Can’t the Fossil Record Tell About Life on Earth?While scientists know much about fossilized organisms and the nature of life on Earth in the past, the fact is that this knowledge is the result of a _______________ number of fossils compared to the sheer number of organisms that lived at one time or another on Earth. Scientists estimate that only about __________ of organisms who ever lived were fossilized due to the fact that fossils are only formed in a limited set of circumstances—usually something catastrophic like a flash flood—and fossils are usually formed from organisms with hard parts like bones or shells.
True or False:There is definite evidence of life on Earth within the first billion years of Earth's existence.Fill in the Blank:One leading hypothesis for the Cambrian Explosion states that levels of _____ in the atmosphere first reached levels close to today's levels.Which of the following features of plants appear last in the fossil record?FlowersSeedsRootsFruitFill in the Blank:Fossils indicate that Dunkelosteusspecimens held the same ecological niche and could grow to the size of a _____. (Hope you watched the video!)Fill in the Blank:About _____% of all organisms who have ever existed have a fossilized specimen.