Trace any branch back through time to see how it connects to any other of life's major branches. Use the curved time scale to find when their common ancestor lived. Five mass extinctions are marked by an abrupt decrease in life's diversity, followed by renewed diversity.
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The geologic time scale on the Great Tree of Life begins at the center bottom, at Earth's birth, more than four thousand million (4 billion) years ago. As you move away from this center point toward the outer margin of the tree, geologic time gets younger and younger, until at the outer curved edge of the tree you arrive at the present day.
Times on the geologic time scale are shown at the base of the diagram in millions of years before present. These are traced through the tree of life along curved, dashed time lines.
- All points on a curved, dashed time line are of the same age. For example; any point on the dashed time line labeled '1000' represents a time 1000 million years (that's equal to one billion years) in the past.
- Similarly, any point on the outer margin of the tree represents time today. Any point on the tree of life can be placed in geologic time by using these curved time lines.
Biological evolution proposes that all living things, including humans, have a common ancestor with any other living thing. On the Great Tree of Life you can explore when in the distant past these common ancestors lived. For example, explore when the common ancestor between fish and humans lived by using the partial Great Tree of Life diagram below. Begin by tracing the human branch back through time along the yellow guide lines. Start at the point on the outer margin of the tree (in other words, today) that is labeled 'humans'. Follow it back in time down the dark brown mammal branch to where it joins the light brown mammal-like reptile branch, then continue back to the point where you meet the bright blue fish branch. This point on the Great Tree of Life represents the common ancestor between humans and fish (in this case, salmon), and, by using the time scale, you can see that this creature lived roughly 440 million years ago. You could reach this same common ancestor by tracing from modern salmon. The time of a common ancestor between any two of life's branches, large or small, on the Great Tree of Life can be found in the same way.
Evolutionary Scale of Relatedness
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Grand tree of life study shows a clock-like
trend in new species emergence and diversity
March 3, 2015
"The constant rate of diversification that we have found indicates that the ecological niches of life are not being filled up and saturated," said Temple professor S. Blair Hedges, a member of the research team's study, published in the early online edition of the journal Molecular Biology and Evolution. "This is contrary to the popular alternative model which predicts a slowing down of diversification as niches fill up with species."
The tree of life compiled by the Temple team is depicted in a new way —- a cosmologically-inspired galaxy of life view —- and contains more than 50,000 species in a tapestry spiraling out from the origin of life.
For the massive meta-study effort, researchers painstakingly assembled data from 2,274 molecular studies, with 96 percent published in the last decade. They built new computer algorithms and tools to synthesize this largest collection of evolutionary peer-reviewed species diversity timelines published to date to produce this Time Tree of Life.
The study also challenges the conventional view of adaptation being the principal force driving species diversification, but rather, underscores the importance of random genetic events and geographic isolation in speciation, taking about 2 million years on average for a new species to emerge onto the scene.
"This finding shows that speciation is more clock-like than people have thought," said Hedges. "Taken together, this indicates that speciation and diversification are separate processes from adaptation, responding more to isolation and time. Adaptation is definitely occurring, so this does not disagree with Darwinism. But it goes against the popular idea that adaptation drives speciation, and against the related concept of punctuated equilibrium which associates adaptive change with speciation."
Besides the new evolutionary insights gained in this study, their Timetree of Life will provide opportunities for researchers to make other discoveries across disciplines, wherever an evolutionary perspective is needed, including, for example, studies of disease and medicine, and the effect of climate change on future species diversity.
Researchers around the world utilize molecular clocks to estimate species divergence times, calculating DNA mutational rates with species divergence times from gene and genomic sequences, that together with the fossil record and geological history, provide a constantly improving view of Darwin's "grandeur of life."
These new results add to the decade-long efforts of the Timetree of Life initiative (TTOL), which includes internet tools and a book, led by team members Hedges and Sudhir Kumar. "The ultimate goal of the TTOL is to chart the timescale of life—to discover when each species and all their ancestors originated, all the way back to the origin of life some four billion years ago," said Hedges.
As an ongoing service to the scientific community, Hedges and Kumar plan to continue adding new data to TTOL from future peer-reviewed studies. They also will improve their current tools, such as web and smartphone apps, and develop new tools, that will make it easier to access the information and to explore the TTOL, and for scientists to update the growing tree with their new data.
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|source link - The tree of life compiled by Temple University researchers is depicted in a new way -- a cosmologically inspired galaxy of life view -- and contains more than 50,000 species in a tapestry spiraling out from the origin of life. | Credit: Temple University|