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History of Life

Scientists determined the earth is about _______ years old. 4.55 billion
At first formation, what was earth like? Mostly magma until denser compounds in the magma sank to form earth's core after thousands of years. The magma cooled and formed the Earth's crust
True or False: Earth’s initial environmental conditions made it difficult for life forms to arise. True. The atmosphere was full of carbon dioxide and ammonia.
According to fossil evidence, what is the earliest form of life? Prokaryotic cells.
When did photosynthesis first evolve? The process of photosynthesis first evolved on Earth about three billion years ago. This began to change the composition of the atmosphere.
When did eukaryotic cells and multicellular organisms evolve? Around 2 billion years ago.
When did land plants first evolve? 475 million years ago.
When did plants with seeds evolve? 400 million years ago.
When did ancestors of modern flowering plants evolve? 130 million years ago.
When was the Cambrian Explosion? A period of rapid growth in life's diversity from 540 to 485 million years ago.
About 650 million years ago what happened? The first simple animals appeared. Sponges, jellies, and other small marine creatures were some of the first animals to evolve on Earth.
About 580 million years ago what happened? The first animals with bilateral symmetry evolved. At first, these were very simple, but over millions of years, these invertebrates developed into more complex, worm-like animals.
About 550 million years ago what happened? Early arthropods first appeared (such as Trilobites). Much later, these organisms eventually became the first life forms to walk on land. The earliest fish-like organisms also appeared. These later diversified into the vertebrates.
About 500 million years ago what happened? Proto-amphibians first appeared. Some of these mostly sea-dwelling species began to develop lungs, which allowed them to leave the water and colonize the land. These vertebrate life forms had symmetric limbs and fully functioning lungs.
About 360 million years ago what happened? Amphibians evolved out of their “proto” phase to become some of the most dominant animals on land. Frogs and toads are examples of modern-day amphibians that resemble these ancient life forms.
About 300 million years ago what happened? Some amphibians evolved into organisms that scientists call “reptile-like amphibians.” They developed short legs and long bodies and were able to live almost exclusively on land. These organisms in turn evolved into reptiles.
What period of time were dinosaurs on Earth? 230 million - 65 million years ago
About 225 million years ago what happened? Mammals first appeared on Earth.
About 150 million years ago what happened? Birds evolved from a line of reptiles.
Around 65 million years ago what happened? First primates evolved.
About 2.5 million years ago what happened? The genus Homo first appeared on Earth.
As early as 300,000 years ago what happened? Modern humans emerged.
Around 25,000 years ago what happened? Neanderthals became extinct.
Explain biodiversity. The variety of life in an area. Most commonly, biodiversity refers to the number of species in an area—species diversity. Species diversity arises due to natural selection acting upon genetic diversity within populations.
What is the general rule for biodiversity? Biodiversity is greatest at low latitudes (nearer the equator) and lowest at high latitudes (nearer the poles).
True or False: When an ecosystem comes under stress, its biodiversity is usually reduced. Large or rapid changes in conditions can lead to extensive loss of biodiversity. True.
What is speciation? The process through which a new species forms.
What could make a population's gene pool isolated? Geographic or biological barriers
What is episodic speciation? When does it occur? How new species evolve when there are major shifts in the environmental conditions of an area. Episodic speciation occurs after mass extinction events.
How many mass extinctions have taken place in Earth's history? 5
What is the purpose of evolutionary trees? Evolutionary trees provide scientists with a way to map extinction and speciation.
True or False: Fossils can never be destroyed. False. Fossils are continually being destroyed.
What is the sequential record of life on Earth? Older fossils are laid down before the younger ones. This creates a sequential record of life on Earth.
A scientist looking at animal fossils from 400 million years ago might see the first appearance of which organism? Insects
When did multicellular life forms appear? About 1 billion years ago
Created by: JustEmma
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