  Ethereum is one of the most popular blockchain systems that supports more
than half a million transactions every day and fosters miscellaneous
decentralized applications with its Turing-complete smart contract machine.
Whereas it remains mysterious what the transaction pattern of Ethereum is and
how it evolves over time. In this paper, we study the evolutionary behavior of
Ethereum transactions from a temporal graph point of view. We first develop a
data analytics platform to collect external transactions associated with users
as well as internal transactions initiated by smart contracts. Three types of
temporal graphs, user-to-user, contract-to-contract and user-contract graphs,
are constructed according to trading relationship and are segmented with an
appropriate time window. We observe a strong correlation between the size of
user-to-user transaction graph and the average Ether price in a time window,
while no evidence of such linkage is shown at the average degree, average edge
weights and average triplet closure duration. The macroscopic and microscopic
burstiness of Ethereum transactions is validated. We analyze the Gini indexes
of the transaction graphs and the user wealth in which Ethereum is found to be
very unfair since the very beginning, in a sense, "the rich is already very
rich".
